From 6e8ec2552c7d13991148e551e3325a624d73fac6 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sun, 16 Jan 2022 14:23:10 +0100 Subject: random: use computational hash for entropy extraction The current 4096-bit LFSR used for entropy collection had a few desirable attributes for the context in which it was created. For example, the state was huge, which meant that /dev/random would be able to output quite a bit of accumulated entropy before blocking. It was also, in its time, quite fast at accumulating entropy byte-by-byte, which matters given the varying contexts in which mix_pool_bytes() is called. And its diffusion was relatively high, which meant that changes would ripple across several words of state rather quickly. However, it also suffers from a few security vulnerabilities. In particular, inputs learned by an attacker can be undone, but moreover, if the state of the pool leaks, its contents can be controlled and entirely zeroed out. I've demonstrated this attack with this SMT2 script, , which Boolector/CaDiCal solves in a matter of seconds on a single core of my laptop, resulting in little proof of concept C demonstrators such as . For basically all recent formal models of RNGs, these attacks represent a significant cryptographic flaw. But how does this manifest practically? If an attacker has access to the system to such a degree that he can learn the internal state of the RNG, arguably there are other lower hanging vulnerabilities -- side-channel, infoleak, or otherwise -- that might have higher priority. On the other hand, seed files are frequently used on systems that have a hard time generating much entropy on their own, and these seed files, being files, often leak or are duplicated and distributed accidentally, or are even seeded over the Internet intentionally, where their contents might be recorded or tampered with. Seen this way, an otherwise quasi-implausible vulnerability is a bit more practical than initially thought. Another aspect of the current mix_pool_bytes() function is that, while its performance was arguably competitive for the time in which it was created, it's no longer considered so. This patch improves performance significantly: on a high-end CPU, an i7-11850H, it improves performance of mix_pool_bytes() by 225%, and on a low-end CPU, a Cortex-A7, it improves performance by 103%. This commit replaces the LFSR of mix_pool_bytes() with a straight- forward cryptographic hash function, BLAKE2s, which is already in use for pool extraction. Universal hashing with a secret seed was considered too, something along the lines of , but the requirement for a secret seed makes for a chicken & egg problem. Instead we go with a formally proven scheme using a computational hash function, described in sections 5.1, 6.4, and B.1.8 of . BLAKE2s outputs 256 bits, which should give us an appropriate amount of min-entropy accumulation, and a wide enough margin of collision resistance against active attacks. mix_pool_bytes() becomes a simple call to blake2s_update(), for accumulation, while the extraction step becomes a blake2s_final() to generate a seed, with which we can then do a HKDF-like or BLAKE2X-like expansion, the first part of which we fold back as an init key for subsequent blake2s_update()s, and the rest we produce to the caller. This then is provided to our CRNG like usual. In that expansion step, we make opportunistic use of 32 bytes of RDRAND output, just as before. We also always reseed the crng with 32 bytes, unconditionally, or not at all, rather than sometimes with 16 as before, as we don't win anything by limiting beyond the 16 byte threshold. Going for a hash function as an entropy collector is a conservative, proven approach. The result of all this is a much simpler and much less bespoke construction than what's there now, which not only plugs a vulnerability but also improves performance considerably. Cc: Theodore Ts'o Cc: Dominik Brodowski Reviewed-by: Eric Biggers Reviewed-by: Greg Kroah-Hartman Reviewed-by: Jean-Philippe Aumasson Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 304 +++++++++----------------------------------------- 1 file changed, 55 insertions(+), 249 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 3404a91edf29..882f78829a24 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -42,61 +42,6 @@ */ /* - * (now, with legal B.S. out of the way.....) - * - * This routine gathers environmental noise from device drivers, etc., - * and returns good random numbers, suitable for cryptographic use. - * Besides the obvious cryptographic uses, these numbers are also good - * for seeding TCP sequence numbers, and other places where it is - * desirable to have numbers which are not only random, but hard to - * predict by an attacker. - * - * Theory of operation - * =================== - * - * Computers are very predictable devices. Hence it is extremely hard - * to produce truly random numbers on a computer --- as opposed to - * pseudo-random numbers, which can easily generated by using a - * algorithm. Unfortunately, it is very easy for attackers to guess - * the sequence of pseudo-random number generators, and for some - * applications this is not acceptable. So instead, we must try to - * gather "environmental noise" from the computer's environment, which - * must be hard for outside attackers to observe, and use that to - * generate random numbers. In a Unix environment, this is best done - * from inside the kernel. - * - * Sources of randomness from the environment include inter-keyboard - * timings, inter-interrupt timings from some interrupts, and other - * events which are both (a) non-deterministic and (b) hard for an - * outside observer to measure. Randomness from these sources are - * added to an "entropy pool", which is mixed using a CRC-like function. - * This is not cryptographically strong, but it is adequate assuming - * the randomness is not chosen maliciously, and it is fast enough that - * the overhead of doing it on every interrupt is very reasonable. - * As random bytes are mixed into the entropy pool, the routines keep - * an *estimate* of how many bits of randomness have been stored into - * the random number generator's internal state. - * - * When random bytes are desired, they are obtained by taking the BLAKE2s - * hash of the contents of the "entropy pool". The BLAKE2s hash avoids - * exposing the internal state of the entropy pool. It is believed to - * be computationally infeasible to derive any useful information - * about the input of BLAKE2s from its output. Even if it is possible to - * analyze BLAKE2s in some clever way, as long as the amount of data - * returned from the generator is less than the inherent entropy in - * the pool, the output data is totally unpredictable. For this - * reason, the routine decreases its internal estimate of how many - * bits of "true randomness" are contained in the entropy pool as it - * outputs random numbers. - * - * If this estimate goes to zero, the routine can still generate - * random numbers; however, an attacker may (at least in theory) be - * able to infer the future output of the generator from prior - * outputs. This requires successful cryptanalysis of BLAKE2s, which is - * not believed to be feasible, but there is a remote possibility. - * Nonetheless, these numbers should be useful for the vast majority - * of purposes. - * * Exported interfaces ---- output * =============================== * @@ -298,23 +243,6 @@ * * mknod /dev/random c 1 8 * mknod /dev/urandom c 1 9 - * - * Acknowledgements: - * ================= - * - * Ideas for constructing this random number generator were derived - * from Pretty Good Privacy's random number generator, and from private - * discussions with Phil Karn. Colin Plumb provided a faster random - * number generator, which speed up the mixing function of the entropy - * pool, taken from PGPfone. Dale Worley has also contributed many - * useful ideas and suggestions to improve this driver. - * - * Any flaws in the design are solely my responsibility, and should - * not be attributed to the Phil, Colin, or any of authors of PGP. - * - * Further background information on this topic may be obtained from - * RFC 1750, "Randomness Recommendations for Security", by Donald - * Eastlake, Steve Crocker, and Jeff Schiller. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt @@ -358,79 +286,15 @@ /* #define ADD_INTERRUPT_BENCH */ -/* - * If the entropy count falls under this number of bits, then we - * should wake up processes which are selecting or polling on write - * access to /dev/random. - */ -static int random_write_wakeup_bits = 28 * (1 << 5); - -/* - * Originally, we used a primitive polynomial of degree .poolwords - * over GF(2). The taps for various sizes are defined below. They - * were chosen to be evenly spaced except for the last tap, which is 1 - * to get the twisting happening as fast as possible. - * - * For the purposes of better mixing, we use the CRC-32 polynomial as - * well to make a (modified) twisted Generalized Feedback Shift - * Register. (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR - * generators. ACM Transactions on Modeling and Computer Simulation - * 2(3):179-194. Also see M. Matsumoto & Y. Kurita, 1994. Twisted - * GFSR generators II. ACM Transactions on Modeling and Computer - * Simulation 4:254-266) - * - * Thanks to Colin Plumb for suggesting this. - * - * The mixing operation is much less sensitive than the output hash, - * where we use BLAKE2s. All that we want of mixing operation is that - * it be a good non-cryptographic hash; i.e. it not produce collisions - * when fed "random" data of the sort we expect to see. As long as - * the pool state differs for different inputs, we have preserved the - * input entropy and done a good job. The fact that an intelligent - * attacker can construct inputs that will produce controlled - * alterations to the pool's state is not important because we don't - * consider such inputs to contribute any randomness. The only - * property we need with respect to them is that the attacker can't - * increase his/her knowledge of the pool's state. Since all - * additions are reversible (knowing the final state and the input, - * you can reconstruct the initial state), if an attacker has any - * uncertainty about the initial state, he/she can only shuffle that - * uncertainty about, but never cause any collisions (which would - * decrease the uncertainty). - * - * Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and - * Videau in their paper, "The Linux Pseudorandom Number Generator - * Revisited" (see: http://eprint.iacr.org/2012/251.pdf). In their - * paper, they point out that we are not using a true Twisted GFSR, - * since Matsumoto & Kurita used a trinomial feedback polynomial (that - * is, with only three taps, instead of the six that we are using). - * As a result, the resulting polynomial is neither primitive nor - * irreducible, and hence does not have a maximal period over - * GF(2**32). They suggest a slight change to the generator - * polynomial which improves the resulting TGFSR polynomial to be - * irreducible, which we have made here. - */ enum poolinfo { - POOL_WORDS = 128, - POOL_WORDMASK = POOL_WORDS - 1, - POOL_BYTES = POOL_WORDS * sizeof(u32), - POOL_BITS = POOL_BYTES * 8, + POOL_BITS = BLAKE2S_HASH_SIZE * 8, POOL_BITSHIFT = ilog2(POOL_BITS), /* To allow fractional bits to be tracked, the entropy_count field is * denominated in units of 1/8th bits. */ POOL_ENTROPY_SHIFT = 3, #define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT) - POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT, - - /* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */ - POOL_TAP1 = 104, - POOL_TAP2 = 76, - POOL_TAP3 = 51, - POOL_TAP4 = 25, - POOL_TAP5 = 1, - - EXTRACT_SIZE = BLAKE2S_HASH_SIZE / 2 + POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT }; /* @@ -438,6 +302,12 @@ enum poolinfo { */ static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); static struct fasync_struct *fasync; +/* + * If the entropy count falls under this number of bits, then we + * should wake up processes which are selecting or polling on write + * access to /dev/random. + */ +static int random_write_wakeup_bits = POOL_BITS * 3 / 4; static DEFINE_SPINLOCK(random_ready_list_lock); static LIST_HEAD(random_ready_list); @@ -493,73 +363,31 @@ MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression"); * **********************************************************************/ -static u32 input_pool_data[POOL_WORDS] __latent_entropy; - static struct { + struct blake2s_state hash; spinlock_t lock; - u16 add_ptr; - u16 input_rotate; int entropy_count; } input_pool = { + .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE), + BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4, + BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 }, + .hash.outlen = BLAKE2S_HASH_SIZE, .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), }; -static ssize_t extract_entropy(void *buf, size_t nbytes, int min); -static ssize_t _extract_entropy(void *buf, size_t nbytes); +static bool extract_entropy(void *buf, size_t nbytes, int min); +static void _extract_entropy(void *buf, size_t nbytes); static void crng_reseed(struct crng_state *crng, bool use_input_pool); -static const u32 twist_table[8] = { - 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158, - 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 }; - /* * This function adds bytes into the entropy "pool". It does not * update the entropy estimate. The caller should call * credit_entropy_bits if this is appropriate. - * - * The pool is stirred with a primitive polynomial of the appropriate - * degree, and then twisted. We twist by three bits at a time because - * it's cheap to do so and helps slightly in the expected case where - * the entropy is concentrated in the low-order bits. */ static void _mix_pool_bytes(const void *in, int nbytes) { - unsigned long i; - int input_rotate; - const u8 *bytes = in; - u32 w; - - input_rotate = input_pool.input_rotate; - i = input_pool.add_ptr; - - /* mix one byte at a time to simplify size handling and churn faster */ - while (nbytes--) { - w = rol32(*bytes++, input_rotate); - i = (i - 1) & POOL_WORDMASK; - - /* XOR in the various taps */ - w ^= input_pool_data[i]; - w ^= input_pool_data[(i + POOL_TAP1) & POOL_WORDMASK]; - w ^= input_pool_data[(i + POOL_TAP2) & POOL_WORDMASK]; - w ^= input_pool_data[(i + POOL_TAP3) & POOL_WORDMASK]; - w ^= input_pool_data[(i + POOL_TAP4) & POOL_WORDMASK]; - w ^= input_pool_data[(i + POOL_TAP5) & POOL_WORDMASK]; - - /* Mix the result back in with a twist */ - input_pool_data[i] = (w >> 3) ^ twist_table[w & 7]; - - /* - * Normally, we add 7 bits of rotation to the pool. - * At the beginning of the pool, add an extra 7 bits - * rotation, so that successive passes spread the - * input bits across the pool evenly. - */ - input_rotate = (input_rotate + (i ? 7 : 14)) & 31; - } - - input_pool.input_rotate = input_rotate; - input_pool.add_ptr = i; + blake2s_update(&input_pool.hash, in, nbytes); } static void __mix_pool_bytes(const void *in, int nbytes) @@ -953,15 +781,14 @@ static int crng_slow_load(const u8 *cp, size_t len) static void crng_reseed(struct crng_state *crng, bool use_input_pool) { unsigned long flags; - int i, num; + int i; union { u8 block[CHACHA_BLOCK_SIZE]; u32 key[8]; } buf; if (use_input_pool) { - num = extract_entropy(&buf, 32, 16); - if (num == 0) + if (!extract_entropy(&buf, 32, 16)) return; } else { _extract_crng(&primary_crng, buf.block); @@ -1329,74 +1156,48 @@ retry: } /* - * This function does the actual extraction for extract_entropy. - * - * Note: we assume that .poolwords is a multiple of 16 words. + * This is an HKDF-like construction for using the hashed collected entropy + * as a PRF key, that's then expanded block-by-block. */ -static void extract_buf(u8 *out) +static void _extract_entropy(void *buf, size_t nbytes) { - struct blake2s_state state __aligned(__alignof__(unsigned long)); - u8 hash[BLAKE2S_HASH_SIZE]; - unsigned long *salt; unsigned long flags; - - blake2s_init(&state, sizeof(hash)); - - /* - * If we have an architectural hardware random number - * generator, use it for BLAKE2's salt & personal fields. - */ - for (salt = (unsigned long *)&state.h[4]; - salt < (unsigned long *)&state.h[8]; ++salt) { - unsigned long v; - if (!arch_get_random_long(&v)) - break; - *salt ^= v; + u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; + struct { + unsigned long rdrand[32 / sizeof(long)]; + size_t counter; + } block; + size_t i; + + for (i = 0; i < ARRAY_SIZE(block.rdrand); ++i) { + if (!arch_get_random_long(&block.rdrand[i])) + block.rdrand[i] = random_get_entropy(); } - /* Generate a hash across the pool */ spin_lock_irqsave(&input_pool.lock, flags); - blake2s_update(&state, (const u8 *)input_pool_data, POOL_BYTES); - blake2s_final(&state, hash); /* final zeros out state */ - /* - * We mix the hash back into the pool to prevent backtracking - * attacks (where the attacker knows the state of the pool - * plus the current outputs, and attempts to find previous - * outputs), unless the hash function can be inverted. By - * mixing at least a hash worth of hash data back, we make - * brute-forcing the feedback as hard as brute-forcing the - * hash. - */ - __mix_pool_bytes(hash, sizeof(hash)); - spin_unlock_irqrestore(&input_pool.lock, flags); + /* seed = HASHPRF(last_key, entropy_input) */ + blake2s_final(&input_pool.hash, seed); - /* Note that EXTRACT_SIZE is half of hash size here, because above - * we've dumped the full length back into mixer. By reducing the - * amount that we emit, we retain a level of forward secrecy. - */ - memcpy(out, hash, EXTRACT_SIZE); - memzero_explicit(hash, sizeof(hash)); -} + /* next_key = HASHPRF(seed, RDRAND || 0) */ + block.counter = 0; + blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed)); + blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key)); -static ssize_t _extract_entropy(void *buf, size_t nbytes) -{ - ssize_t ret = 0, i; - u8 tmp[EXTRACT_SIZE]; + spin_unlock_irqrestore(&input_pool.lock, flags); + memzero_explicit(next_key, sizeof(next_key)); while (nbytes) { - extract_buf(tmp); - i = min_t(int, nbytes, EXTRACT_SIZE); - memcpy(buf, tmp, i); + i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE); + /* output = HASHPRF(seed, RDRAND || ++counter) */ + ++block.counter; + blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed)); nbytes -= i; buf += i; - ret += i; } - /* Wipe data just returned from memory */ - memzero_explicit(tmp, sizeof(tmp)); - - return ret; + memzero_explicit(seed, sizeof(seed)); + memzero_explicit(&block, sizeof(block)); } /* @@ -1404,13 +1205,18 @@ static ssize_t _extract_entropy(void *buf, size_t nbytes) * returns it in a buffer. * * The min parameter specifies the minimum amount we can pull before - * failing to avoid races that defeat catastrophic reseeding. + * failing to avoid races that defeat catastrophic reseeding. If we + * have less than min entropy available, we return false and buf is + * not filled. */ -static ssize_t extract_entropy(void *buf, size_t nbytes, int min) +static bool extract_entropy(void *buf, size_t nbytes, int min) { trace_extract_entropy(nbytes, POOL_ENTROPY_BITS(), _RET_IP_); - nbytes = account(nbytes, min); - return _extract_entropy(buf, nbytes); + if (account(nbytes, min)) { + _extract_entropy(buf, nbytes); + return true; + } + return false; } #define warn_unseeded_randomness(previous) \ @@ -1674,7 +1480,7 @@ static void __init init_std_data(void) unsigned long rv; mix_pool_bytes(&now, sizeof(now)); - for (i = POOL_BYTES; i > 0; i -= sizeof(rv)) { + for (i = BLAKE2S_BLOCK_SIZE; i > 0; i -= sizeof(rv)) { if (!arch_get_random_seed_long(&rv) && !arch_get_random_long(&rv)) rv = random_get_entropy(); -- cgit v1.2.3 From 9c07f57869e90140080cfc282cc628d123e27704 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 2 Feb 2022 13:30:03 +0100 Subject: random: simplify entropy debiting Our pool is 256 bits, and we only ever use all of it or don't use it at all, which is decided by whether or not it has at least 128 bits in it. So we can drastically simplify the accounting and cmpxchg loop to do exactly this. While we're at it, we move the minimum bit size into a constant so it can be shared between the two places where it matters. The reason we want any of this is for the case in which an attacker has compromised the current state, and then bruteforces small amounts of entropy added to it. By demanding a particular minimum amount of entropy be present before reseeding, we make that bruteforcing difficult. Note that this rationale no longer includes anything about /dev/random blocking at the right moment, since /dev/random no longer blocks (except for at ~boot), but rather uses the crng. In a former life, /dev/random was different and therefore required a more nuanced account(), but this is no longer. Behaviorally, nothing changes here. This is just a simplification of the code. Cc: Theodore Ts'o Cc: Greg Kroah-Hartman Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 91 ++++++++++--------------------------------- include/trace/events/random.h | 30 +++----------- 2 files changed, 27 insertions(+), 94 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 882f78829a24..9014fd54da64 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -289,12 +289,14 @@ enum poolinfo { POOL_BITS = BLAKE2S_HASH_SIZE * 8, POOL_BITSHIFT = ilog2(POOL_BITS), + POOL_MIN_BITS = POOL_BITS / 2, /* To allow fractional bits to be tracked, the entropy_count field is * denominated in units of 1/8th bits. */ POOL_ENTROPY_SHIFT = 3, #define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT) - POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT + POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT, + POOL_MIN_FRACBITS = POOL_MIN_BITS << POOL_ENTROPY_SHIFT }; /* @@ -375,8 +377,7 @@ static struct { .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), }; -static bool extract_entropy(void *buf, size_t nbytes, int min); -static void _extract_entropy(void *buf, size_t nbytes); +static void extract_entropy(void *buf, size_t nbytes); static void crng_reseed(struct crng_state *crng, bool use_input_pool); @@ -467,7 +468,7 @@ static void process_random_ready_list(void) */ static void credit_entropy_bits(int nbits) { - int entropy_count, entropy_bits, orig; + int entropy_count, orig; int nfrac = nbits << POOL_ENTROPY_SHIFT; /* Ensure that the multiplication can avoid being 64 bits wide. */ @@ -527,8 +528,7 @@ retry: trace_credit_entropy_bits(nbits, entropy_count >> POOL_ENTROPY_SHIFT, _RET_IP_); - entropy_bits = entropy_count >> POOL_ENTROPY_SHIFT; - if (crng_init < 2 && entropy_bits >= 128) + if (crng_init < 2 && entropy_count >= POOL_MIN_FRACBITS) crng_reseed(&primary_crng, true); } @@ -618,7 +618,7 @@ static void crng_initialize_secondary(struct crng_state *crng) static void __init crng_initialize_primary(void) { - _extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); + extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); if (crng_init_try_arch_early() && trust_cpu && crng_init < 2) { invalidate_batched_entropy(); numa_crng_init(); @@ -788,8 +788,17 @@ static void crng_reseed(struct crng_state *crng, bool use_input_pool) } buf; if (use_input_pool) { - if (!extract_entropy(&buf, 32, 16)) - return; + int entropy_count; + do { + entropy_count = READ_ONCE(input_pool.entropy_count); + if (entropy_count < POOL_MIN_FRACBITS) + return; + } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); + extract_entropy(buf.key, sizeof(buf.key)); + if (random_write_wakeup_bits) { + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + } } else { _extract_crng(&primary_crng, buf.block); _crng_backtrack_protect(&primary_crng, buf.block, @@ -1114,52 +1123,11 @@ EXPORT_SYMBOL_GPL(add_disk_randomness); * *********************************************************************/ -/* - * This function decides how many bytes to actually take from the - * given pool, and also debits the entropy count accordingly. - */ -static size_t account(size_t nbytes, int min) -{ - int entropy_count, orig; - size_t ibytes, nfrac; - - BUG_ON(input_pool.entropy_count > POOL_FRACBITS); - - /* Can we pull enough? */ -retry: - entropy_count = orig = READ_ONCE(input_pool.entropy_count); - if (WARN_ON(entropy_count < 0)) { - pr_warn("negative entropy count: count %d\n", entropy_count); - entropy_count = 0; - } - - /* never pull more than available */ - ibytes = min_t(size_t, nbytes, entropy_count >> (POOL_ENTROPY_SHIFT + 3)); - if (ibytes < min) - ibytes = 0; - nfrac = ibytes << (POOL_ENTROPY_SHIFT + 3); - if ((size_t)entropy_count > nfrac) - entropy_count -= nfrac; - else - entropy_count = 0; - - if (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig) - goto retry; - - trace_debit_entropy(8 * ibytes); - if (ibytes && POOL_ENTROPY_BITS() < random_write_wakeup_bits) { - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } - - return ibytes; -} - /* * This is an HKDF-like construction for using the hashed collected entropy * as a PRF key, that's then expanded block-by-block. */ -static void _extract_entropy(void *buf, size_t nbytes) +static void extract_entropy(void *buf, size_t nbytes) { unsigned long flags; u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; @@ -1169,6 +1137,8 @@ static void _extract_entropy(void *buf, size_t nbytes) } block; size_t i; + trace_extract_entropy(nbytes, POOL_ENTROPY_BITS()); + for (i = 0; i < ARRAY_SIZE(block.rdrand); ++i) { if (!arch_get_random_long(&block.rdrand[i])) block.rdrand[i] = random_get_entropy(); @@ -1200,25 +1170,6 @@ static void _extract_entropy(void *buf, size_t nbytes) memzero_explicit(&block, sizeof(block)); } -/* - * This function extracts randomness from the "entropy pool", and - * returns it in a buffer. - * - * The min parameter specifies the minimum amount we can pull before - * failing to avoid races that defeat catastrophic reseeding. If we - * have less than min entropy available, we return false and buf is - * not filled. - */ -static bool extract_entropy(void *buf, size_t nbytes, int min) -{ - trace_extract_entropy(nbytes, POOL_ENTROPY_BITS(), _RET_IP_); - if (account(nbytes, min)) { - _extract_entropy(buf, nbytes); - return true; - } - return false; -} - #define warn_unseeded_randomness(previous) \ _warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous)) diff --git a/include/trace/events/random.h b/include/trace/events/random.h index a2d9aa16a5d7..ad149aeaf42c 100644 --- a/include/trace/events/random.h +++ b/include/trace/events/random.h @@ -79,22 +79,6 @@ TRACE_EVENT(credit_entropy_bits, __entry->bits, __entry->entropy_count, (void *)__entry->IP) ); -TRACE_EVENT(debit_entropy, - TP_PROTO(int debit_bits), - - TP_ARGS( debit_bits), - - TP_STRUCT__entry( - __field( int, debit_bits ) - ), - - TP_fast_assign( - __entry->debit_bits = debit_bits; - ), - - TP_printk("input pool: debit_bits %d", __entry->debit_bits) -); - TRACE_EVENT(add_input_randomness, TP_PROTO(int input_bits), @@ -161,31 +145,29 @@ DEFINE_EVENT(random__get_random_bytes, get_random_bytes_arch, ); DECLARE_EVENT_CLASS(random__extract_entropy, - TP_PROTO(int nbytes, int entropy_count, unsigned long IP), + TP_PROTO(int nbytes, int entropy_count), - TP_ARGS(nbytes, entropy_count, IP), + TP_ARGS(nbytes, entropy_count), TP_STRUCT__entry( __field( int, nbytes ) __field( int, entropy_count ) - __field(unsigned long, IP ) ), TP_fast_assign( __entry->nbytes = nbytes; __entry->entropy_count = entropy_count; - __entry->IP = IP; ), - TP_printk("input pool: nbytes %d entropy_count %d caller %pS", - __entry->nbytes, __entry->entropy_count, (void *)__entry->IP) + TP_printk("input pool: nbytes %d entropy_count %d", + __entry->nbytes, __entry->entropy_count) ); DEFINE_EVENT(random__extract_entropy, extract_entropy, - TP_PROTO(int nbytes, int entropy_count, unsigned long IP), + TP_PROTO(int nbytes, int entropy_count), - TP_ARGS(nbytes, entropy_count, IP) + TP_ARGS(nbytes, entropy_count) ); TRACE_EVENT(urandom_read, -- cgit v1.2.3 From c570449094844527577c5c914140222cb1893e3f Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 3 Feb 2022 13:28:06 +0100 Subject: random: use linear min-entropy accumulation crediting MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 30e37ec516ae ("random: account for entropy loss due to overwrites") assumed that adding new entropy to the LFSR pool probabilistically cancelled out old entropy there, so entropy was credited asymptotically, approximating Shannon entropy of independent sources (rather than a stronger min-entropy notion) using 1/8th fractional bits and replacing a constant 2-2/√𝑒 term (~0.786938) with 3/4 (0.75) to slightly underestimate it. This wasn't superb, but it was perhaps better than nothing, so that's what was done. Which entropy specifically was being cancelled out and how much precisely each time is hard to tell, though as I showed with the attack code in my previous commit, a motivated adversary with sufficient information can actually cancel out everything. Since we're no longer using an LFSR for entropy accumulation, this probabilistic cancellation is no longer relevant. Rather, we're now using a computational hash function as the accumulator and we've switched to working in the random oracle model, from which we can now revisit the question of min-entropy accumulation, which is done in detail in . Consider a long input bit string that is built by concatenating various smaller independent input bit strings. Each one of these inputs has a designated min-entropy, which is what we're passing to credit_entropy_bits(h). When we pass the concatenation of these to a random oracle, it means that an adversary trying to receive back the same reply as us would need to become certain about each part of the concatenated bit string we passed in, which means becoming certain about all of those h values. That means we can estimate the accumulation by simply adding up the h values in calls to credit_entropy_bits(h); there's no probabilistic cancellation at play like there was said to be for the LFSR. Incidentally, this is also what other entropy accumulators based on computational hash functions do as well. So this commit replaces credit_entropy_bits(h) with essentially `total = min(POOL_BITS, total + h)`, done with a cmpxchg loop as before. What if we're wrong and the above is nonsense? It's not, but let's assume we don't want the actual _behavior_ of the code to change much. Currently that behavior is not extracting from the input pool until it has 128 bits of entropy in it. With the old algorithm, we'd hit that magic 128 number after roughly 256 calls to credit_entropy_bits(1). So, we can retain more or less the old behavior by waiting to extract from the input pool until it hits 256 bits of entropy using the new code. For people concerned about this change, it means that there's not that much practical behavioral change. And for folks actually trying to model the behavior rigorously, it means that we have an even higher margin against attacks. Cc: Theodore Ts'o Cc: Dominik Brodowski Cc: Greg Kroah-Hartman Reviewed-by: Eric Biggers Reviewed-by: Jean-Philippe Aumasson Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 114 +++++++++----------------------------------------- 1 file changed, 20 insertions(+), 94 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 9014fd54da64..20538e9b1a2c 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -286,17 +286,9 @@ /* #define ADD_INTERRUPT_BENCH */ -enum poolinfo { +enum { POOL_BITS = BLAKE2S_HASH_SIZE * 8, - POOL_BITSHIFT = ilog2(POOL_BITS), - POOL_MIN_BITS = POOL_BITS / 2, - - /* To allow fractional bits to be tracked, the entropy_count field is - * denominated in units of 1/8th bits. */ - POOL_ENTROPY_SHIFT = 3, -#define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT) - POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT, - POOL_MIN_FRACBITS = POOL_MIN_BITS << POOL_ENTROPY_SHIFT + POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ }; /* @@ -309,7 +301,7 @@ static struct fasync_struct *fasync; * should wake up processes which are selecting or polling on write * access to /dev/random. */ -static int random_write_wakeup_bits = POOL_BITS * 3 / 4; +static int random_write_wakeup_bits = POOL_MIN_BITS; static DEFINE_SPINLOCK(random_ready_list_lock); static LIST_HEAD(random_ready_list); @@ -469,66 +461,18 @@ static void process_random_ready_list(void) static void credit_entropy_bits(int nbits) { int entropy_count, orig; - int nfrac = nbits << POOL_ENTROPY_SHIFT; - - /* Ensure that the multiplication can avoid being 64 bits wide. */ - BUILD_BUG_ON(2 * (POOL_ENTROPY_SHIFT + POOL_BITSHIFT) > 31); if (!nbits) return; -retry: - entropy_count = orig = READ_ONCE(input_pool.entropy_count); - if (nfrac < 0) { - /* Debit */ - entropy_count += nfrac; - } else { - /* - * Credit: we have to account for the possibility of - * overwriting already present entropy. Even in the - * ideal case of pure Shannon entropy, new contributions - * approach the full value asymptotically: - * - * entropy <- entropy + (pool_size - entropy) * - * (1 - exp(-add_entropy/pool_size)) - * - * For add_entropy <= pool_size/2 then - * (1 - exp(-add_entropy/pool_size)) >= - * (add_entropy/pool_size)*0.7869... - * so we can approximate the exponential with - * 3/4*add_entropy/pool_size and still be on the - * safe side by adding at most pool_size/2 at a time. - * - * The use of pool_size-2 in the while statement is to - * prevent rounding artifacts from making the loop - * arbitrarily long; this limits the loop to log2(pool_size)*2 - * turns no matter how large nbits is. - */ - int pnfrac = nfrac; - const int s = POOL_BITSHIFT + POOL_ENTROPY_SHIFT + 2; - /* The +2 corresponds to the /4 in the denominator */ - - do { - unsigned int anfrac = min(pnfrac, POOL_FRACBITS / 2); - unsigned int add = - ((POOL_FRACBITS - entropy_count) * anfrac * 3) >> s; - - entropy_count += add; - pnfrac -= anfrac; - } while (unlikely(entropy_count < POOL_FRACBITS - 2 && pnfrac)); - } - - if (WARN_ON(entropy_count < 0)) { - pr_warn("negative entropy/overflow: count %d\n", entropy_count); - entropy_count = 0; - } else if (entropy_count > POOL_FRACBITS) - entropy_count = POOL_FRACBITS; - if (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig) - goto retry; + do { + orig = READ_ONCE(input_pool.entropy_count); + entropy_count = min(POOL_BITS, orig + nbits); + } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); - trace_credit_entropy_bits(nbits, entropy_count >> POOL_ENTROPY_SHIFT, _RET_IP_); + trace_credit_entropy_bits(nbits, entropy_count, _RET_IP_); - if (crng_init < 2 && entropy_count >= POOL_MIN_FRACBITS) + if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) crng_reseed(&primary_crng, true); } @@ -791,7 +735,7 @@ static void crng_reseed(struct crng_state *crng, bool use_input_pool) int entropy_count; do { entropy_count = READ_ONCE(input_pool.entropy_count); - if (entropy_count < POOL_MIN_FRACBITS) + if (entropy_count < POOL_MIN_BITS) return; } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); extract_entropy(buf.key, sizeof(buf.key)); @@ -1014,7 +958,7 @@ void add_input_randomness(unsigned int type, unsigned int code, last_value = value; add_timer_randomness(&input_timer_state, (type << 4) ^ code ^ (code >> 4) ^ value); - trace_add_input_randomness(POOL_ENTROPY_BITS()); + trace_add_input_randomness(input_pool.entropy_count); } EXPORT_SYMBOL_GPL(add_input_randomness); @@ -1112,7 +1056,7 @@ void add_disk_randomness(struct gendisk *disk) return; /* first major is 1, so we get >= 0x200 here */ add_timer_randomness(disk->random, 0x100 + disk_devt(disk)); - trace_add_disk_randomness(disk_devt(disk), POOL_ENTROPY_BITS()); + trace_add_disk_randomness(disk_devt(disk), input_pool.entropy_count); } EXPORT_SYMBOL_GPL(add_disk_randomness); #endif @@ -1137,7 +1081,7 @@ static void extract_entropy(void *buf, size_t nbytes) } block; size_t i; - trace_extract_entropy(nbytes, POOL_ENTROPY_BITS()); + trace_extract_entropy(nbytes, input_pool.entropy_count); for (i = 0; i < ARRAY_SIZE(block.rdrand); ++i) { if (!arch_get_random_long(&block.rdrand[i])) @@ -1486,9 +1430,9 @@ static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, { int ret; - nbytes = min_t(size_t, nbytes, INT_MAX >> (POOL_ENTROPY_SHIFT + 3)); + nbytes = min_t(size_t, nbytes, INT_MAX >> 6); ret = extract_crng_user(buf, nbytes); - trace_urandom_read(8 * nbytes, 0, POOL_ENTROPY_BITS()); + trace_urandom_read(8 * nbytes, 0, input_pool.entropy_count); return ret; } @@ -1527,7 +1471,7 @@ static __poll_t random_poll(struct file *file, poll_table *wait) mask = 0; if (crng_ready()) mask |= EPOLLIN | EPOLLRDNORM; - if (POOL_ENTROPY_BITS() < random_write_wakeup_bits) + if (input_pool.entropy_count < random_write_wakeup_bits) mask |= EPOLLOUT | EPOLLWRNORM; return mask; } @@ -1582,8 +1526,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) switch (cmd) { case RNDGETENTCNT: /* inherently racy, no point locking */ - ent_count = POOL_ENTROPY_BITS(); - if (put_user(ent_count, p)) + if (put_user(input_pool.entropy_count, p)) return -EFAULT; return 0; case RNDADDTOENTCNT: @@ -1734,23 +1677,6 @@ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer, return proc_dostring(&fake_table, write, buffer, lenp, ppos); } -/* - * Return entropy available scaled to integral bits - */ -static int proc_do_entropy(struct ctl_table *table, int write, void *buffer, - size_t *lenp, loff_t *ppos) -{ - struct ctl_table fake_table; - int entropy_count; - - entropy_count = *(int *)table->data >> POOL_ENTROPY_SHIFT; - - fake_table.data = &entropy_count; - fake_table.maxlen = sizeof(entropy_count); - - return proc_dointvec(&fake_table, write, buffer, lenp, ppos); -} - static int sysctl_poolsize = POOL_BITS; static struct ctl_table random_table[] = { { @@ -1762,10 +1688,10 @@ static struct ctl_table random_table[] = { }, { .procname = "entropy_avail", + .data = &input_pool.entropy_count, .maxlen = sizeof(int), .mode = 0444, - .proc_handler = proc_do_entropy, - .data = &input_pool.entropy_count, + .proc_handler = proc_dointvec, }, { .procname = "write_wakeup_threshold", @@ -1972,7 +1898,7 @@ void add_hwgenerator_randomness(const char *buffer, size_t count, */ wait_event_interruptible_timeout(random_write_wait, !system_wq || kthread_should_stop() || - POOL_ENTROPY_BITS() <= random_write_wakeup_bits, + input_pool.entropy_count <= random_write_wakeup_bits, CRNG_RESEED_INTERVAL); mix_pool_bytes(buffer, count); credit_entropy_bits(entropy); -- cgit v1.2.3 From 489c7fc44b5740d377e8cfdbf0851036e493af00 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sat, 5 Feb 2022 14:00:58 +0100 Subject: random: always wake up entropy writers after extraction Now that POOL_BITS == POOL_MIN_BITS, we must unconditionally wake up entropy writers after every extraction. Therefore there's no point of write_wakeup_threshold, so we can move it to the dustbin of unused compatibility sysctls. While we're at it, we can fix a small comparison where we were waking up after <= min rather than < min. Cc: Theodore Ts'o Suggested-by: Eric Biggers Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- Documentation/admin-guide/sysctl/kernel.rst | 7 ++++-- drivers/char/random.c | 33 ++++++++++------------------- 2 files changed, 16 insertions(+), 24 deletions(-) diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index d359bcfadd39..d3c6d9a501a9 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -1029,14 +1029,17 @@ This is a directory, with the following entries: * ``poolsize``: the entropy pool size, in bits; * ``urandom_min_reseed_secs``: obsolete (used to determine the minimum - number of seconds between urandom pool reseeding). + number of seconds between urandom pool reseeding). This file is + writable for compatibility purposes, but writing to it has no effect + on any RNG behavior. * ``uuid``: a UUID generated every time this is retrieved (this can thus be used to generate UUIDs at will); * ``write_wakeup_threshold``: when the entropy count drops below this (as a number of bits), processes waiting to write to ``/dev/random`` - are woken up. + are woken up. This file is writable for compatibility purposes, but + writing to it has no effect on any RNG behavior. If ``drivers/char/random.c`` is built with ``ADD_INTERRUPT_BENCH`` defined, these additional entries are present: diff --git a/drivers/char/random.c b/drivers/char/random.c index 20538e9b1a2c..3b30e764eeef 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -296,12 +296,6 @@ enum { */ static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); static struct fasync_struct *fasync; -/* - * If the entropy count falls under this number of bits, then we - * should wake up processes which are selecting or polling on write - * access to /dev/random. - */ -static int random_write_wakeup_bits = POOL_MIN_BITS; static DEFINE_SPINLOCK(random_ready_list_lock); static LIST_HEAD(random_ready_list); @@ -739,10 +733,8 @@ static void crng_reseed(struct crng_state *crng, bool use_input_pool) return; } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); extract_entropy(buf.key, sizeof(buf.key)); - if (random_write_wakeup_bits) { - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); } else { _extract_crng(&primary_crng, buf.block); _crng_backtrack_protect(&primary_crng, buf.block, @@ -1471,7 +1463,7 @@ static __poll_t random_poll(struct file *file, poll_table *wait) mask = 0; if (crng_ready()) mask |= EPOLLIN | EPOLLRDNORM; - if (input_pool.entropy_count < random_write_wakeup_bits) + if (input_pool.entropy_count < POOL_MIN_BITS) mask |= EPOLLOUT | EPOLLWRNORM; return mask; } @@ -1556,7 +1548,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; - if (xchg(&input_pool.entropy_count, 0) && random_write_wakeup_bits) { + if (xchg(&input_pool.entropy_count, 0)) { wake_up_interruptible(&random_write_wait); kill_fasync(&fasync, SIGIO, POLL_OUT); } @@ -1636,9 +1628,9 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, #include -static int min_write_thresh; -static int max_write_thresh = POOL_BITS; static int random_min_urandom_seed = 60; +static int random_write_wakeup_bits = POOL_MIN_BITS; +static int sysctl_poolsize = POOL_BITS; static char sysctl_bootid[16]; /* @@ -1677,7 +1669,6 @@ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer, return proc_dostring(&fake_table, write, buffer, lenp, ppos); } -static int sysctl_poolsize = POOL_BITS; static struct ctl_table random_table[] = { { .procname = "poolsize", @@ -1698,9 +1689,7 @@ static struct ctl_table random_table[] = { .data = &random_write_wakeup_bits, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec_minmax, - .extra1 = &min_write_thresh, - .extra2 = &max_write_thresh, + .proc_handler = proc_dointvec, }, { .procname = "urandom_min_reseed_secs", @@ -1892,13 +1881,13 @@ void add_hwgenerator_randomness(const char *buffer, size_t count, } /* Throttle writing if we're above the trickle threshold. - * We'll be woken up again once below random_write_wakeup_thresh, - * when the calling thread is about to terminate, or once - * CRNG_RESEED_INTERVAL has lapsed. + * We'll be woken up again once below POOL_MIN_BITS, when + * the calling thread is about to terminate, or once + * CRNG_RESEED_INTERVAL has elapsed. */ wait_event_interruptible_timeout(random_write_wait, !system_wq || kthread_should_stop() || - input_pool.entropy_count <= random_write_wakeup_bits, + input_pool.entropy_count < POOL_MIN_BITS, CRNG_RESEED_INTERVAL); mix_pool_bytes(buffer, count); credit_entropy_bits(entropy); -- cgit v1.2.3 From a49c010e61e1938be851f5e49ac219d49b704103 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 4 Feb 2022 01:45:53 +0100 Subject: random: make credit_entropy_bits() always safe This is called from various hwgenerator drivers, so rather than having one "safe" version for userspace and one "unsafe" version for the kernel, just make everything safe; the checks are cheap and sensible to have anyway. Reported-by: Sultan Alsawaf Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 29 +++++++++-------------------- 1 file changed, 9 insertions(+), 20 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 3b30e764eeef..92aca0a539e0 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -447,18 +447,15 @@ static void process_random_ready_list(void) spin_unlock_irqrestore(&random_ready_list_lock, flags); } -/* - * Credit (or debit) the entropy store with n bits of entropy. - * Use credit_entropy_bits_safe() if the value comes from userspace - * or otherwise should be checked for extreme values. - */ static void credit_entropy_bits(int nbits) { int entropy_count, orig; - if (!nbits) + if (nbits <= 0) return; + nbits = min(nbits, POOL_BITS); + do { orig = READ_ONCE(input_pool.entropy_count); entropy_count = min(POOL_BITS, orig + nbits); @@ -470,18 +467,6 @@ static void credit_entropy_bits(int nbits) crng_reseed(&primary_crng, true); } -static int credit_entropy_bits_safe(int nbits) -{ - if (nbits < 0) - return -EINVAL; - - /* Cap the value to avoid overflows */ - nbits = min(nbits, POOL_BITS); - - credit_entropy_bits(nbits); - return 0; -} - /********************************************************************* * * CRNG using CHACHA20 @@ -1526,7 +1511,10 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) return -EPERM; if (get_user(ent_count, p)) return -EFAULT; - return credit_entropy_bits_safe(ent_count); + if (ent_count < 0) + return -EINVAL; + credit_entropy_bits(ent_count); + return 0; case RNDADDENTROPY: if (!capable(CAP_SYS_ADMIN)) return -EPERM; @@ -1539,7 +1527,8 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) retval = write_pool((const char __user *)p, size); if (retval < 0) return retval; - return credit_entropy_bits_safe(ent_count); + credit_entropy_bits(ent_count); + return 0; case RNDZAPENTCNT: case RNDCLEARPOOL: /* -- cgit v1.2.3 From 5d58ea3a31cc98b9fa563f6921d3d043bf0103d1 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Fri, 4 Feb 2022 14:17:33 -0800 Subject: random: remove use_input_pool parameter from crng_reseed() The primary_crng is always reseeded from the input_pool, while the NUMA crngs are always reseeded from the primary_crng. Remove the redundant 'use_input_pool' parameter from crng_reseed() and just directly check whether the crng is the primary_crng. Signed-off-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 92aca0a539e0..968c415d1f45 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -365,7 +365,7 @@ static struct { static void extract_entropy(void *buf, size_t nbytes); -static void crng_reseed(struct crng_state *crng, bool use_input_pool); +static void crng_reseed(struct crng_state *crng); /* * This function adds bytes into the entropy "pool". It does not @@ -464,7 +464,7 @@ static void credit_entropy_bits(int nbits) trace_credit_entropy_bits(nbits, entropy_count, _RET_IP_); if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) - crng_reseed(&primary_crng, true); + crng_reseed(&primary_crng); } /********************************************************************* @@ -701,7 +701,7 @@ static int crng_slow_load(const u8 *cp, size_t len) return 1; } -static void crng_reseed(struct crng_state *crng, bool use_input_pool) +static void crng_reseed(struct crng_state *crng) { unsigned long flags; int i; @@ -710,7 +710,7 @@ static void crng_reseed(struct crng_state *crng, bool use_input_pool) u32 key[8]; } buf; - if (use_input_pool) { + if (crng == &primary_crng) { int entropy_count; do { entropy_count = READ_ONCE(input_pool.entropy_count); @@ -748,7 +748,7 @@ static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE]) init_time = READ_ONCE(crng->init_time); if (time_after(READ_ONCE(crng_global_init_time), init_time) || time_after(jiffies, init_time + CRNG_RESEED_INTERVAL)) - crng_reseed(crng, crng == &primary_crng); + crng_reseed(crng); } spin_lock_irqsave(&crng->lock, flags); chacha20_block(&crng->state[0], out); @@ -1547,7 +1547,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) return -EPERM; if (crng_init < 2) return -ENODATA; - crng_reseed(&primary_crng, true); + crng_reseed(&primary_crng); WRITE_ONCE(crng_global_init_time, jiffies - 1); return 0; default: -- cgit v1.2.3 From 77760fd7f7ae3dfd03668204e708d1568d75447d Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 28 Jan 2022 23:29:45 +0100 Subject: random: remove batched entropy locking MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Rather than use spinlocks to protect batched entropy, we can instead disable interrupts locally, since we're dealing with per-cpu data, and manage resets with a basic generation counter. At the same time, we can't quite do this on PREEMPT_RT, where we still want spinlocks-as- mutexes semantics. So we use a local_lock_t, which provides the right behavior for each. Because this is a per-cpu lock, that generation counter is still doing the necessary CPU-to-CPU communication. This should improve performance a bit. It will also fix the linked splat that Jonathan received with a PROVE_RAW_LOCK_NESTING=y. Reviewed-by: Sebastian Andrzej Siewior Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Suggested-by: Andy Lutomirski Reported-by: Jonathan NeuschĂ€fer Tested-by: Jonathan NeuschĂ€fer Link: https://lore.kernel.org/lkml/YfMa0QgsjCVdRAvJ@latitude/ Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 55 ++++++++++++++++++++++++++------------------------- 1 file changed, 28 insertions(+), 27 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 968c415d1f45..ceded1c4f73b 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1731,13 +1731,16 @@ static int __init random_sysctls_init(void) device_initcall(random_sysctls_init); #endif /* CONFIG_SYSCTL */ +static atomic_t batch_generation = ATOMIC_INIT(0); + struct batched_entropy { union { u64 entropy_u64[CHACHA_BLOCK_SIZE / sizeof(u64)]; u32 entropy_u32[CHACHA_BLOCK_SIZE / sizeof(u32)]; }; + local_lock_t lock; unsigned int position; - spinlock_t batch_lock; + int generation; }; /* @@ -1749,7 +1752,7 @@ struct batched_entropy { * point prior. */ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = { - .batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u64.lock), + .lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock) }; u64 get_random_u64(void) @@ -1758,67 +1761,65 @@ u64 get_random_u64(void) unsigned long flags; struct batched_entropy *batch; static void *previous; + int next_gen; warn_unseeded_randomness(&previous); + local_lock_irqsave(&batched_entropy_u64.lock, flags); batch = raw_cpu_ptr(&batched_entropy_u64); - spin_lock_irqsave(&batch->batch_lock, flags); - if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) { + + next_gen = atomic_read(&batch_generation); + if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0 || + next_gen != batch->generation) { extract_crng((u8 *)batch->entropy_u64); batch->position = 0; + batch->generation = next_gen; } + ret = batch->entropy_u64[batch->position++]; - spin_unlock_irqrestore(&batch->batch_lock, flags); + local_unlock_irqrestore(&batched_entropy_u64.lock, flags); return ret; } EXPORT_SYMBOL(get_random_u64); static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = { - .batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u32.lock), + .lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock) }; + u32 get_random_u32(void) { u32 ret; unsigned long flags; struct batched_entropy *batch; static void *previous; + int next_gen; warn_unseeded_randomness(&previous); + local_lock_irqsave(&batched_entropy_u32.lock, flags); batch = raw_cpu_ptr(&batched_entropy_u32); - spin_lock_irqsave(&batch->batch_lock, flags); - if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) { + + next_gen = atomic_read(&batch_generation); + if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0 || + next_gen != batch->generation) { extract_crng((u8 *)batch->entropy_u32); batch->position = 0; + batch->generation = next_gen; } + ret = batch->entropy_u32[batch->position++]; - spin_unlock_irqrestore(&batch->batch_lock, flags); + local_unlock_irqrestore(&batched_entropy_u32.lock, flags); return ret; } EXPORT_SYMBOL(get_random_u32); /* It's important to invalidate all potential batched entropy that might * be stored before the crng is initialized, which we can do lazily by - * simply resetting the counter to zero so that it's re-extracted on the - * next usage. */ + * bumping the generation counter. + */ static void invalidate_batched_entropy(void) { - int cpu; - unsigned long flags; - - for_each_possible_cpu(cpu) { - struct batched_entropy *batched_entropy; - - batched_entropy = per_cpu_ptr(&batched_entropy_u32, cpu); - spin_lock_irqsave(&batched_entropy->batch_lock, flags); - batched_entropy->position = 0; - spin_unlock(&batched_entropy->batch_lock); - - batched_entropy = per_cpu_ptr(&batched_entropy_u64, cpu); - spin_lock(&batched_entropy->batch_lock); - batched_entropy->position = 0; - spin_unlock_irqrestore(&batched_entropy->batch_lock, flags); - } + atomic_inc(&batch_generation); } /** -- cgit v1.2.3 From 7c2fe2b32bf76441ff5b7a425b384e5f75aa530a Mon Sep 17 00:00:00 2001 From: Dominik Brodowski Date: Sat, 5 Feb 2022 11:34:57 +0100 Subject: random: fix locking in crng_fast_load() crng_init is protected by primary_crng->lock, so keep holding that lock when incrementing crng_init from 0 to 1 in crng_fast_load(). The call to pr_notice() can wait until the lock is released; this code path cannot be reached twice, as crng_fast_load() aborts early if crng_init > 0. Signed-off-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index ceded1c4f73b..79cf577e5086 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -647,12 +647,13 @@ static size_t crng_fast_load(const u8 *cp, size_t len) p[crng_init_cnt % CHACHA_KEY_SIZE] ^= *cp; cp++; crng_init_cnt++; len--; ret++; } - spin_unlock_irqrestore(&primary_crng.lock, flags); if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { invalidate_batched_entropy(); crng_init = 1; - pr_notice("fast init done\n"); } + spin_unlock_irqrestore(&primary_crng.lock, flags); + if (crng_init == 1) + pr_notice("fast init done\n"); return ret; } -- cgit v1.2.3 From 28f425e573e906a4c15f8392cc2b1561ef448595 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Feb 2022 12:18:33 +0100 Subject: random: use RDSEED instead of RDRAND in entropy extraction When /dev/random was directly connected with entropy extraction, without any expansion stage, extract_buf() was called for every 10 bytes of data read from /dev/random. For that reason, RDRAND was used rather than RDSEED. At the same time, crng_reseed() was still only called every 5 minutes, so there RDSEED made sense. Those olden days were also a time when the entropy collector did not use a cryptographic hash function, which meant most bets were off in terms of real preimage resistance. For that reason too it didn't matter _that_ much whether RDSEED was mixed in before or after entropy extraction; both choices were sort of bad. But now we have a cryptographic hash function at work, and with that we get real preimage resistance. We also now only call extract_entropy() every 5 minutes, rather than every 10 bytes. This allows us to do two important things. First, we can switch to using RDSEED in extract_entropy(), as Dominik suggested. Second, we can ensure that RDSEED input always goes into the cryptographic hash function with other things before being used directly. This eliminates a category of attacks in which the CPU knows the current state of the crng and knows that we're going to xor RDSEED into it, and so it computes a malicious RDSEED. By going through our hash function, it would require the CPU to compute a preimage on the fly, which isn't going to happen. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Suggested-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 22 +++++++++------------- 1 file changed, 9 insertions(+), 13 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 79cf577e5086..41f42d887513 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -727,13 +727,8 @@ static void crng_reseed(struct crng_state *crng) CHACHA_KEY_SIZE); } spin_lock_irqsave(&crng->lock, flags); - for (i = 0; i < 8; i++) { - unsigned long rv; - if (!arch_get_random_seed_long(&rv) && - !arch_get_random_long(&rv)) - rv = random_get_entropy(); - crng->state[i + 4] ^= buf.key[i] ^ rv; - } + for (i = 0; i < 8; i++) + crng->state[i + 4] ^= buf.key[i]; memzero_explicit(&buf, sizeof(buf)); WRITE_ONCE(crng->init_time, jiffies); spin_unlock_irqrestore(&crng->lock, flags); @@ -1054,16 +1049,17 @@ static void extract_entropy(void *buf, size_t nbytes) unsigned long flags; u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; struct { - unsigned long rdrand[32 / sizeof(long)]; + unsigned long rdseed[32 / sizeof(long)]; size_t counter; } block; size_t i; trace_extract_entropy(nbytes, input_pool.entropy_count); - for (i = 0; i < ARRAY_SIZE(block.rdrand); ++i) { - if (!arch_get_random_long(&block.rdrand[i])) - block.rdrand[i] = random_get_entropy(); + for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) { + if (!arch_get_random_seed_long(&block.rdseed[i]) && + !arch_get_random_long(&block.rdseed[i])) + block.rdseed[i] = random_get_entropy(); } spin_lock_irqsave(&input_pool.lock, flags); @@ -1071,7 +1067,7 @@ static void extract_entropy(void *buf, size_t nbytes) /* seed = HASHPRF(last_key, entropy_input) */ blake2s_final(&input_pool.hash, seed); - /* next_key = HASHPRF(seed, RDRAND || 0) */ + /* next_key = HASHPRF(seed, RDSEED || 0) */ block.counter = 0; blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed)); blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key)); @@ -1081,7 +1077,7 @@ static void extract_entropy(void *buf, size_t nbytes) while (nbytes) { i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE); - /* output = HASHPRF(seed, RDRAND || ++counter) */ + /* output = HASHPRF(seed, RDSEED || ++counter) */ ++block.counter; blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed)); nbytes -= i; -- cgit v1.2.3 From a9412d510ab9a9ba411fea612903631d2e1f1601 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sun, 6 Feb 2022 23:51:41 +0100 Subject: random: get rid of secondary crngs As the comment said, this is indeed a "hack". Since it was introduced, it's been a constant state machine nightmare, with lots of subtle early boot issues and a wildly complex set of machinery to keep everything in sync. Rather than continuing to play whack-a-mole with this approach, this commit simply removes it entirely. This commit is preparation for "random: use simpler fast key erasure flow on per-cpu keys" in this series, which introduces a simpler (and faster) mechanism to accomplish the same thing. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 225 ++++++++++++-------------------------------------- 1 file changed, 53 insertions(+), 172 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 41f42d887513..be4922e09cc5 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -323,14 +323,11 @@ static struct crng_state primary_crng = { * its value (from 0->1->2). */ static int crng_init = 0; -static bool crng_need_final_init = false; #define crng_ready() (likely(crng_init > 1)) static int crng_init_cnt = 0; -static unsigned long crng_global_init_time = 0; #define CRNG_INIT_CNT_THRESH (2 * CHACHA_KEY_SIZE) -static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE]); -static void _crng_backtrack_protect(struct crng_state *crng, - u8 tmp[CHACHA_BLOCK_SIZE], int used); +static void extract_crng(u8 out[CHACHA_BLOCK_SIZE]); +static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used); static void process_random_ready_list(void); static void _get_random_bytes(void *buf, int nbytes); @@ -365,7 +362,7 @@ static struct { static void extract_entropy(void *buf, size_t nbytes); -static void crng_reseed(struct crng_state *crng); +static void crng_reseed(void); /* * This function adds bytes into the entropy "pool". It does not @@ -464,7 +461,7 @@ static void credit_entropy_bits(int nbits) trace_credit_entropy_bits(nbits, entropy_count, _RET_IP_); if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) - crng_reseed(&primary_crng); + crng_reseed(); } /********************************************************************* @@ -477,16 +474,7 @@ static void credit_entropy_bits(int nbits) static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); -/* - * Hack to deal with crazy userspace progams when they are all trying - * to access /dev/urandom in parallel. The programs are almost - * certainly doing something terribly wrong, but we'll work around - * their brain damage. - */ -static struct crng_state **crng_node_pool __read_mostly; - static void invalidate_batched_entropy(void); -static void numa_crng_init(void); static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); static int __init parse_trust_cpu(char *arg) @@ -495,24 +483,6 @@ static int __init parse_trust_cpu(char *arg) } early_param("random.trust_cpu", parse_trust_cpu); -static bool crng_init_try_arch(struct crng_state *crng) -{ - int i; - bool arch_init = true; - unsigned long rv; - - for (i = 4; i < 16; i++) { - if (!arch_get_random_seed_long(&rv) && - !arch_get_random_long(&rv)) { - rv = random_get_entropy(); - arch_init = false; - } - crng->state[i] ^= rv; - } - - return arch_init; -} - static bool __init crng_init_try_arch_early(void) { int i; @@ -531,100 +501,17 @@ static bool __init crng_init_try_arch_early(void) return arch_init; } -static void crng_initialize_secondary(struct crng_state *crng) -{ - chacha_init_consts(crng->state); - _get_random_bytes(&crng->state[4], sizeof(u32) * 12); - crng_init_try_arch(crng); - crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1; -} - -static void __init crng_initialize_primary(void) +static void __init crng_initialize(void) { extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); if (crng_init_try_arch_early() && trust_cpu && crng_init < 2) { invalidate_batched_entropy(); - numa_crng_init(); crng_init = 2; pr_notice("crng init done (trusting CPU's manufacturer)\n"); } primary_crng.init_time = jiffies - CRNG_RESEED_INTERVAL - 1; } -static void crng_finalize_init(void) -{ - if (!system_wq) { - /* We can't call numa_crng_init until we have workqueues, - * so mark this for processing later. */ - crng_need_final_init = true; - return; - } - - invalidate_batched_entropy(); - numa_crng_init(); - crng_init = 2; - crng_need_final_init = false; - process_random_ready_list(); - wake_up_interruptible(&crng_init_wait); - kill_fasync(&fasync, SIGIO, POLL_IN); - pr_notice("crng init done\n"); - if (unseeded_warning.missed) { - pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n", - unseeded_warning.missed); - unseeded_warning.missed = 0; - } - if (urandom_warning.missed) { - pr_notice("%d urandom warning(s) missed due to ratelimiting\n", - urandom_warning.missed); - urandom_warning.missed = 0; - } -} - -static void do_numa_crng_init(struct work_struct *work) -{ - int i; - struct crng_state *crng; - struct crng_state **pool; - - pool = kcalloc(nr_node_ids, sizeof(*pool), GFP_KERNEL | __GFP_NOFAIL); - for_each_online_node(i) { - crng = kmalloc_node(sizeof(struct crng_state), - GFP_KERNEL | __GFP_NOFAIL, i); - spin_lock_init(&crng->lock); - crng_initialize_secondary(crng); - pool[i] = crng; - } - /* pairs with READ_ONCE() in select_crng() */ - if (cmpxchg_release(&crng_node_pool, NULL, pool) != NULL) { - for_each_node(i) - kfree(pool[i]); - kfree(pool); - } -} - -static DECLARE_WORK(numa_crng_init_work, do_numa_crng_init); - -static void numa_crng_init(void) -{ - if (IS_ENABLED(CONFIG_NUMA)) - schedule_work(&numa_crng_init_work); -} - -static struct crng_state *select_crng(void) -{ - if (IS_ENABLED(CONFIG_NUMA)) { - struct crng_state **pool; - int nid = numa_node_id(); - - /* pairs with cmpxchg_release() in do_numa_crng_init() */ - pool = READ_ONCE(crng_node_pool); - if (pool && pool[nid]) - return pool[nid]; - } - - return &primary_crng; -} - /* * crng_fast_load() can be called by code in the interrupt service * path. So we can't afford to dilly-dally. Returns the number of @@ -702,68 +589,71 @@ static int crng_slow_load(const u8 *cp, size_t len) return 1; } -static void crng_reseed(struct crng_state *crng) +static void crng_reseed(void) { unsigned long flags; - int i; + int i, entropy_count; union { u8 block[CHACHA_BLOCK_SIZE]; u32 key[8]; } buf; - if (crng == &primary_crng) { - int entropy_count; - do { - entropy_count = READ_ONCE(input_pool.entropy_count); - if (entropy_count < POOL_MIN_BITS) - return; - } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); - extract_entropy(buf.key, sizeof(buf.key)); - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } else { - _extract_crng(&primary_crng, buf.block); - _crng_backtrack_protect(&primary_crng, buf.block, - CHACHA_KEY_SIZE); - } - spin_lock_irqsave(&crng->lock, flags); + do { + entropy_count = READ_ONCE(input_pool.entropy_count); + if (entropy_count < POOL_MIN_BITS) + return; + } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); + extract_entropy(buf.key, sizeof(buf.key)); + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + + spin_lock_irqsave(&primary_crng.lock, flags); for (i = 0; i < 8; i++) - crng->state[i + 4] ^= buf.key[i]; + primary_crng.state[i + 4] ^= buf.key[i]; memzero_explicit(&buf, sizeof(buf)); - WRITE_ONCE(crng->init_time, jiffies); - spin_unlock_irqrestore(&crng->lock, flags); - if (crng == &primary_crng && crng_init < 2) - crng_finalize_init(); + WRITE_ONCE(primary_crng.init_time, jiffies); + spin_unlock_irqrestore(&primary_crng.lock, flags); + if (crng_init < 2) { + invalidate_batched_entropy(); + crng_init = 2; + process_random_ready_list(); + wake_up_interruptible(&crng_init_wait); + kill_fasync(&fasync, SIGIO, POLL_IN); + pr_notice("crng init done\n"); + if (unseeded_warning.missed) { + pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n", + unseeded_warning.missed); + unseeded_warning.missed = 0; + } + if (urandom_warning.missed) { + pr_notice("%d urandom warning(s) missed due to ratelimiting\n", + urandom_warning.missed); + urandom_warning.missed = 0; + } + } } -static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE]) +static void extract_crng(u8 out[CHACHA_BLOCK_SIZE]) { unsigned long flags, init_time; if (crng_ready()) { - init_time = READ_ONCE(crng->init_time); - if (time_after(READ_ONCE(crng_global_init_time), init_time) || - time_after(jiffies, init_time + CRNG_RESEED_INTERVAL)) - crng_reseed(crng); + init_time = READ_ONCE(primary_crng.init_time); + if (time_after(jiffies, init_time + CRNG_RESEED_INTERVAL)) + crng_reseed(); } - spin_lock_irqsave(&crng->lock, flags); - chacha20_block(&crng->state[0], out); - if (crng->state[12] == 0) - crng->state[13]++; - spin_unlock_irqrestore(&crng->lock, flags); -} - -static void extract_crng(u8 out[CHACHA_BLOCK_SIZE]) -{ - _extract_crng(select_crng(), out); + spin_lock_irqsave(&primary_crng.lock, flags); + chacha20_block(&primary_crng.state[0], out); + if (primary_crng.state[12] == 0) + primary_crng.state[13]++; + spin_unlock_irqrestore(&primary_crng.lock, flags); } /* * Use the leftover bytes from the CRNG block output (if there is * enough) to mutate the CRNG key to provide backtracking protection. */ -static void _crng_backtrack_protect(struct crng_state *crng, - u8 tmp[CHACHA_BLOCK_SIZE], int used) +static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used) { unsigned long flags; u32 *s, *d; @@ -774,17 +664,12 @@ static void _crng_backtrack_protect(struct crng_state *crng, extract_crng(tmp); used = 0; } - spin_lock_irqsave(&crng->lock, flags); + spin_lock_irqsave(&primary_crng.lock, flags); s = (u32 *)&tmp[used]; - d = &crng->state[4]; + d = &primary_crng.state[4]; for (i = 0; i < 8; i++) *d++ ^= *s++; - spin_unlock_irqrestore(&crng->lock, flags); -} - -static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used) -{ - _crng_backtrack_protect(select_crng(), tmp, used); + spin_unlock_irqrestore(&primary_crng.lock, flags); } static ssize_t extract_crng_user(void __user *buf, size_t nbytes) @@ -1371,10 +1256,7 @@ static void __init init_std_data(void) int __init rand_initialize(void) { init_std_data(); - if (crng_need_final_init) - crng_finalize_init(); - crng_initialize_primary(); - crng_global_init_time = jiffies; + crng_initialize(); if (ratelimit_disable) { urandom_warning.interval = 0; unseeded_warning.interval = 0; @@ -1544,8 +1426,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) return -EPERM; if (crng_init < 2) return -ENODATA; - crng_reseed(&primary_crng); - WRITE_ONCE(crng_global_init_time, jiffies - 1); + crng_reseed(); return 0; default: return -EINVAL; -- cgit v1.2.3 From 8566417221fcec51346ec164e920dacb979c6b5f Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Feb 2022 12:40:14 +0100 Subject: random: inline leaves of rand_initialize() This is a preparatory commit for the following one. We simply inline the various functions that rand_initialize() calls that have no other callers. The compiler was doing this anyway before. Doing this will allow us to reorganize this after. We can then move the trust_cpu and parse_trust_cpu definitions a bit closer to where they're actually used, which makes the code easier to read. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 90 +++++++++++++++++++-------------------------------- 1 file changed, 33 insertions(+), 57 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index be4922e09cc5..a55a58b9807a 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -476,42 +476,6 @@ static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); static void invalidate_batched_entropy(void); -static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); -static int __init parse_trust_cpu(char *arg) -{ - return kstrtobool(arg, &trust_cpu); -} -early_param("random.trust_cpu", parse_trust_cpu); - -static bool __init crng_init_try_arch_early(void) -{ - int i; - bool arch_init = true; - unsigned long rv; - - for (i = 4; i < 16; i++) { - if (!arch_get_random_seed_long_early(&rv) && - !arch_get_random_long_early(&rv)) { - rv = random_get_entropy(); - arch_init = false; - } - primary_crng.state[i] ^= rv; - } - - return arch_init; -} - -static void __init crng_initialize(void) -{ - extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); - if (crng_init_try_arch_early() && trust_cpu && crng_init < 2) { - invalidate_batched_entropy(); - crng_init = 2; - pr_notice("crng init done (trusting CPU's manufacturer)\n"); - } - primary_crng.init_time = jiffies - CRNG_RESEED_INTERVAL - 1; -} - /* * crng_fast_load() can be called by code in the interrupt service * path. So we can't afford to dilly-dally. Returns the number of @@ -1220,17 +1184,28 @@ int __must_check get_random_bytes_arch(void *buf, int nbytes) } EXPORT_SYMBOL(get_random_bytes_arch); +static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); +static int __init parse_trust_cpu(char *arg) +{ + return kstrtobool(arg, &trust_cpu); +} +early_param("random.trust_cpu", parse_trust_cpu); + /* - * init_std_data - initialize pool with system data - * - * This function clears the pool's entropy count and mixes some system - * data into the pool to prepare it for use. The pool is not cleared - * as that can only decrease the entropy in the pool. + * Note that setup_arch() may call add_device_randomness() + * long before we get here. This allows seeding of the pools + * with some platform dependent data very early in the boot + * process. But it limits our options here. We must use + * statically allocated structures that already have all + * initializations complete at compile time. We should also + * take care not to overwrite the precious per platform data + * we were given. */ -static void __init init_std_data(void) +int __init rand_initialize(void) { int i; ktime_t now = ktime_get_real(); + bool arch_init = true; unsigned long rv; mix_pool_bytes(&now, sizeof(now)); @@ -1241,22 +1216,23 @@ static void __init init_std_data(void) mix_pool_bytes(&rv, sizeof(rv)); } mix_pool_bytes(utsname(), sizeof(*(utsname()))); -} -/* - * Note that setup_arch() may call add_device_randomness() - * long before we get here. This allows seeding of the pools - * with some platform dependent data very early in the boot - * process. But it limits our options here. We must use - * statically allocated structures that already have all - * initializations complete at compile time. We should also - * take care not to overwrite the precious per platform data - * we were given. - */ -int __init rand_initialize(void) -{ - init_std_data(); - crng_initialize(); + extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); + for (i = 4; i < 16; i++) { + if (!arch_get_random_seed_long_early(&rv) && + !arch_get_random_long_early(&rv)) { + rv = random_get_entropy(); + arch_init = false; + } + primary_crng.state[i] ^= rv; + } + if (arch_init && trust_cpu && crng_init < 2) { + invalidate_batched_entropy(); + crng_init = 2; + pr_notice("crng init done (trusting CPU's manufacturer)\n"); + } + primary_crng.init_time = jiffies - CRNG_RESEED_INTERVAL - 1; + if (ratelimit_disable) { urandom_warning.interval = 0; unseeded_warning.interval = 0; -- cgit v1.2.3 From a02cf3d0dd77244fd5333ac48d78871de459ae6d Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Feb 2022 12:44:28 +0100 Subject: random: ensure early RDSEED goes through mixer on init Continuing the reasoning of "random: use RDSEED instead of RDRAND in entropy extraction" from this series, at init time we also don't want to be xoring RDSEED directly into the crng. Instead it's safer to put it into our entropy collector and then re-extract it, so that it goes through a hash function with preimage resistance. As a matter of hygiene, we also order these now so that the RDSEED byte are hashed in first, followed by the bytes that are likely more predictable (e.g. utsname()). Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 16 +++++----------- 1 file changed, 5 insertions(+), 11 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index a55a58b9807a..21a067cf5b4c 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1208,24 +1208,18 @@ int __init rand_initialize(void) bool arch_init = true; unsigned long rv; - mix_pool_bytes(&now, sizeof(now)); for (i = BLAKE2S_BLOCK_SIZE; i > 0; i -= sizeof(rv)) { - if (!arch_get_random_seed_long(&rv) && - !arch_get_random_long(&rv)) - rv = random_get_entropy(); - mix_pool_bytes(&rv, sizeof(rv)); - } - mix_pool_bytes(utsname(), sizeof(*(utsname()))); - - extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); - for (i = 4; i < 16; i++) { if (!arch_get_random_seed_long_early(&rv) && !arch_get_random_long_early(&rv)) { rv = random_get_entropy(); arch_init = false; } - primary_crng.state[i] ^= rv; + mix_pool_bytes(&rv, sizeof(rv)); } + mix_pool_bytes(&now, sizeof(now)); + mix_pool_bytes(utsname(), sizeof(*(utsname()))); + + extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); if (arch_init && trust_cpu && crng_init < 2) { invalidate_batched_entropy(); crng_init = 2; -- cgit v1.2.3 From 91c2afca290ed3034841c8c8532e69ed9e16cf34 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Feb 2022 13:00:11 +0100 Subject: random: do not xor RDRAND when writing into /dev/random Continuing the reasoning of "random: ensure early RDSEED goes through mixer on init", we don't want RDRAND interacting with anything without going through the mixer function, as a backdoored CPU could presumably cancel out data during an xor, which it'd have a harder time doing when being forced through a cryptographic hash function. There's actually no need at all to be calling RDRAND in write_pool(), because before we extract from the pool, we always do so with 32 bytes of RDSEED hashed in at that stage. Xoring at this stage is needless and introduces a minor liability. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 21a067cf5b4c..d31b0b3afe2e 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1305,25 +1305,15 @@ static __poll_t random_poll(struct file *file, poll_table *wait) static int write_pool(const char __user *buffer, size_t count) { size_t bytes; - u32 t, buf[16]; + u8 buf[BLAKE2S_BLOCK_SIZE]; const char __user *p = buffer; while (count > 0) { - int b, i = 0; - bytes = min(count, sizeof(buf)); - if (copy_from_user(&buf, p, bytes)) + if (copy_from_user(buf, p, bytes)) return -EFAULT; - - for (b = bytes; b > 0; b -= sizeof(u32), i++) { - if (!arch_get_random_int(&t)) - break; - buf[i] ^= t; - } - count -= bytes; p += bytes; - mix_pool_bytes(buf, bytes); cond_resched(); } -- cgit v1.2.3 From c30c575db4858f0bbe5e315ff2e529c782f33a1f Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 9 Feb 2022 01:56:35 +0100 Subject: random: absorb fast pool into input pool after fast load During crng_init == 0, we never credit entropy in add_interrupt_ randomness(), but instead dump it directly into the primary_crng. That's fine, except for the fact that we then wind up throwing away that entropy later when we switch to extracting from the input pool and xoring into (and later in this series overwriting) the primary_crng key. The two other early init sites -- add_hwgenerator_randomness()'s use crng_fast_load() and add_device_ randomness()'s use of crng_slow_load() -- always additionally give their inputs to the input pool. But not add_interrupt_randomness(). This commit fixes that shortcoming by calling mix_pool_bytes() after crng_fast_load() in add_interrupt_randomness(). That's partially verboten on PREEMPT_RT, where it implies taking spinlock_t from an IRQ handler. But this also only happens during early boot and then never again after that. Plus it's a trylock so it has the same considerations as calling crng_fast_load(), which we're already using. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Suggested-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index d31b0b3afe2e..f3179c67010b 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -850,6 +850,10 @@ void add_interrupt_randomness(int irq) crng_fast_load((u8 *)fast_pool->pool, sizeof(fast_pool->pool)) > 0) { fast_pool->count = 0; fast_pool->last = now; + if (spin_trylock(&input_pool.lock)) { + _mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool)); + spin_unlock(&input_pool.lock); + } } return; } -- cgit v1.2.3 From 186873c549df11b63e17062f863654e1501e1524 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Mon, 7 Feb 2022 15:08:49 +0100 Subject: random: use simpler fast key erasure flow on per-cpu keys MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Rather than the clunky NUMA full ChaCha state system we had prior, this commit is closer to the original "fast key erasure RNG" proposal from , by simply treating ChaCha keys on a per-cpu basis. All entropy is extracted to a base crng key of 32 bytes. This base crng has a birthdate and a generation counter. When we go to take bytes from the crng, we first check if the birthdate is too old; if it is, we reseed per usual. Then we start working on a per-cpu crng. This per-cpu crng makes sure that it has the same generation counter as the base crng. If it doesn't, it does fast key erasure with the base crng key and uses the output as its new per-cpu key, and then updates its local generation counter. Then, using this per-cpu state, we do ordinary fast key erasure. Half of this first block is used to overwrite the per-cpu crng key for the next call -- this is the fast key erasure RNG idea -- and the other half, along with the ChaCha state, is returned to the caller. If the caller desires more than this remaining half, it can generate more ChaCha blocks, unlocked, using the now detached ChaCha state that was just returned. Crypto-wise, this is more or less what we were doing before, but this simply makes it more explicit and ensures that we always have backtrack protection by not playing games with a shared block counter. The flow looks like this: ──extract()──â–ș base_crng.key ◄──memcpy()───┐ │ │ └──chacha()──────┬─â–ș new_base_key └─â–ș crngs[n].key ◄──memcpy()───┐ │ │ └──chacha()───┬─â–ș new_key └─â–ș random_bytes │ └────â–ș There are a few hairy details around early init. Just as was done before, prior to having gathered enough entropy, crng_fast_load() and crng_slow_load() dump bytes directly into the base crng, and when we go to take bytes from the crng, in that case, we're doing fast key erasure with the base crng rather than the fast unlocked per-cpu crngs. This is fine as that's only the state of affairs during very early boot; once the crng initializes we never use these paths again. In the process of all this, the APIs into the crng become a bit simpler: we have get_random_bytes(buf, len) and get_random_bytes_user(buf, len), which both do what you'd expect. All of the details of fast key erasure and per-cpu selection happen only in a very short critical section of crng_make_state(), which selects the right per-cpu key, does the fast key erasure, and returns a local state to the caller's stack. So, we no longer have a need for a separate backtrack function, as this happens all at once here. The API then allows us to extend backtrack protection to batched entropy without really having to do much at all. The result is a bit simpler than before and has fewer foot guns. The init time state machine also gets a lot simpler as we don't need to wait for workqueues to come online and do deferred work. And the multi-core performance should be increased significantly, by virtue of having hardly any locking on the fast path. Cc: Theodore Ts'o Cc: Dominik Brodowski Cc: Sebastian Andrzej Siewior Reviewed-by: Jann Horn Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 395 +++++++++++++++++++++++++++++--------------------- 1 file changed, 229 insertions(+), 166 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index f3179c67010b..538eaa469f5e 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -67,63 +67,19 @@ * Exported interfaces ---- kernel output * -------------------------------------- * - * The primary kernel interface is + * The primary kernel interfaces are: * * void get_random_bytes(void *buf, int nbytes); - * - * This interface will return the requested number of random bytes, - * and place it in the requested buffer. This is equivalent to a - * read from /dev/urandom. - * - * For less critical applications, there are the functions: - * * u32 get_random_u32() * u64 get_random_u64() * unsigned int get_random_int() * unsigned long get_random_long() * - * These are produced by a cryptographic RNG seeded from get_random_bytes, - * and so do not deplete the entropy pool as much. These are recommended - * for most in-kernel operations *if the result is going to be stored in - * the kernel*. - * - * Specifically, the get_random_int() family do not attempt to do - * "anti-backtracking". If you capture the state of the kernel (e.g. - * by snapshotting the VM), you can figure out previous get_random_int() - * return values. But if the value is stored in the kernel anyway, - * this is not a problem. - * - * It *is* safe to expose get_random_int() output to attackers (e.g. as - * network cookies); given outputs 1..n, it's not feasible to predict - * outputs 0 or n+1. The only concern is an attacker who breaks into - * the kernel later; the get_random_int() engine is not reseeded as - * often as the get_random_bytes() one. - * - * get_random_bytes() is needed for keys that need to stay secret after - * they are erased from the kernel. For example, any key that will - * be wrapped and stored encrypted. And session encryption keys: we'd - * like to know that after the session is closed and the keys erased, - * the plaintext is unrecoverable to someone who recorded the ciphertext. - * - * But for network ports/cookies, stack canaries, PRNG seeds, address - * space layout randomization, session *authentication* keys, or other - * applications where the sensitive data is stored in the kernel in - * plaintext for as long as it's sensitive, the get_random_int() family - * is just fine. - * - * Consider ASLR. We want to keep the address space secret from an - * outside attacker while the process is running, but once the address - * space is torn down, it's of no use to an attacker any more. And it's - * stored in kernel data structures as long as it's alive, so worrying - * about an attacker's ability to extrapolate it from the get_random_int() - * CRNG is silly. - * - * Even some cryptographic keys are safe to generate with get_random_int(). - * In particular, keys for SipHash are generally fine. Here, knowledge - * of the key authorizes you to do something to a kernel object (inject - * packets to a network connection, or flood a hash table), and the - * key is stored with the object being protected. Once it goes away, - * we no longer care if anyone knows the key. + * These interfaces will return the requested number of random bytes + * into the given buffer or as a return value. This is equivalent to a + * read from /dev/urandom. The get_random_{u32,u64,int,long}() family + * of functions may be higher performance for one-off random integers, + * because they do a bit of buffering. * * prandom_u32() * ------------- @@ -300,20 +256,6 @@ static struct fasync_struct *fasync; static DEFINE_SPINLOCK(random_ready_list_lock); static LIST_HEAD(random_ready_list); -struct crng_state { - u32 state[16]; - unsigned long init_time; - spinlock_t lock; -}; - -static struct crng_state primary_crng = { - .lock = __SPIN_LOCK_UNLOCKED(primary_crng.lock), - .state[0] = CHACHA_CONSTANT_EXPA, - .state[1] = CHACHA_CONSTANT_ND_3, - .state[2] = CHACHA_CONSTANT_2_BY, - .state[3] = CHACHA_CONSTANT_TE_K, -}; - /* * crng_init = 0 --> Uninitialized * 1 --> Initialized @@ -325,9 +267,6 @@ static struct crng_state primary_crng = { static int crng_init = 0; #define crng_ready() (likely(crng_init > 1)) static int crng_init_cnt = 0; -#define CRNG_INIT_CNT_THRESH (2 * CHACHA_KEY_SIZE) -static void extract_crng(u8 out[CHACHA_BLOCK_SIZE]); -static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used); static void process_random_ready_list(void); static void _get_random_bytes(void *buf, int nbytes); @@ -470,7 +409,30 @@ static void credit_entropy_bits(int nbits) * *********************************************************************/ -#define CRNG_RESEED_INTERVAL (300 * HZ) +enum { + CRNG_RESEED_INTERVAL = 300 * HZ, + CRNG_INIT_CNT_THRESH = 2 * CHACHA_KEY_SIZE +}; + +static struct { + u8 key[CHACHA_KEY_SIZE] __aligned(__alignof__(long)); + unsigned long birth; + unsigned long generation; + spinlock_t lock; +} base_crng = { + .lock = __SPIN_LOCK_UNLOCKED(base_crng.lock) +}; + +struct crng { + u8 key[CHACHA_KEY_SIZE]; + unsigned long generation; + local_lock_t lock; +}; + +static DEFINE_PER_CPU(struct crng, crngs) = { + .generation = ULONG_MAX, + .lock = INIT_LOCAL_LOCK(crngs.lock), +}; static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); @@ -487,22 +449,22 @@ static size_t crng_fast_load(const u8 *cp, size_t len) u8 *p; size_t ret = 0; - if (!spin_trylock_irqsave(&primary_crng.lock, flags)) + if (!spin_trylock_irqsave(&base_crng.lock, flags)) return 0; if (crng_init != 0) { - spin_unlock_irqrestore(&primary_crng.lock, flags); + spin_unlock_irqrestore(&base_crng.lock, flags); return 0; } - p = (u8 *)&primary_crng.state[4]; + p = base_crng.key; while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) { - p[crng_init_cnt % CHACHA_KEY_SIZE] ^= *cp; + p[crng_init_cnt % sizeof(base_crng.key)] ^= *cp; cp++; crng_init_cnt++; len--; ret++; } if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { invalidate_batched_entropy(); crng_init = 1; } - spin_unlock_irqrestore(&primary_crng.lock, flags); + spin_unlock_irqrestore(&base_crng.lock, flags); if (crng_init == 1) pr_notice("fast init done\n"); return ret; @@ -527,14 +489,14 @@ static int crng_slow_load(const u8 *cp, size_t len) unsigned long flags; static u8 lfsr = 1; u8 tmp; - unsigned int i, max = CHACHA_KEY_SIZE; + unsigned int i, max = sizeof(base_crng.key); const u8 *src_buf = cp; - u8 *dest_buf = (u8 *)&primary_crng.state[4]; + u8 *dest_buf = base_crng.key; - if (!spin_trylock_irqsave(&primary_crng.lock, flags)) + if (!spin_trylock_irqsave(&base_crng.lock, flags)) return 0; if (crng_init != 0) { - spin_unlock_irqrestore(&primary_crng.lock, flags); + spin_unlock_irqrestore(&base_crng.lock, flags); return 0; } if (len > max) @@ -545,38 +507,50 @@ static int crng_slow_load(const u8 *cp, size_t len) lfsr >>= 1; if (tmp & 1) lfsr ^= 0xE1; - tmp = dest_buf[i % CHACHA_KEY_SIZE]; - dest_buf[i % CHACHA_KEY_SIZE] ^= src_buf[i % len] ^ lfsr; + tmp = dest_buf[i % sizeof(base_crng.key)]; + dest_buf[i % sizeof(base_crng.key)] ^= src_buf[i % len] ^ lfsr; lfsr += (tmp << 3) | (tmp >> 5); } - spin_unlock_irqrestore(&primary_crng.lock, flags); + spin_unlock_irqrestore(&base_crng.lock, flags); return 1; } static void crng_reseed(void) { unsigned long flags; - int i, entropy_count; - union { - u8 block[CHACHA_BLOCK_SIZE]; - u32 key[8]; - } buf; + int entropy_count; + unsigned long next_gen; + u8 key[CHACHA_KEY_SIZE]; + /* + * First we make sure we have POOL_MIN_BITS of entropy in the pool, + * and then we drain all of it. Only then can we extract a new key. + */ do { entropy_count = READ_ONCE(input_pool.entropy_count); if (entropy_count < POOL_MIN_BITS) return; } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); - extract_entropy(buf.key, sizeof(buf.key)); + extract_entropy(key, sizeof(key)); wake_up_interruptible(&random_write_wait); kill_fasync(&fasync, SIGIO, POLL_OUT); - spin_lock_irqsave(&primary_crng.lock, flags); - for (i = 0; i < 8; i++) - primary_crng.state[i + 4] ^= buf.key[i]; - memzero_explicit(&buf, sizeof(buf)); - WRITE_ONCE(primary_crng.init_time, jiffies); - spin_unlock_irqrestore(&primary_crng.lock, flags); + /* + * We copy the new key into the base_crng, overwriting the old one, + * and update the generation counter. We avoid hitting ULONG_MAX, + * because the per-cpu crngs are initialized to ULONG_MAX, so this + * forces new CPUs that come online to always initialize. + */ + spin_lock_irqsave(&base_crng.lock, flags); + memcpy(base_crng.key, key, sizeof(base_crng.key)); + next_gen = base_crng.generation + 1; + if (next_gen == ULONG_MAX) + ++next_gen; + WRITE_ONCE(base_crng.generation, next_gen); + WRITE_ONCE(base_crng.birth, jiffies); + spin_unlock_irqrestore(&base_crng.lock, flags); + memzero_explicit(key, sizeof(key)); + if (crng_init < 2) { invalidate_batched_entropy(); crng_init = 2; @@ -597,77 +571,143 @@ static void crng_reseed(void) } } -static void extract_crng(u8 out[CHACHA_BLOCK_SIZE]) +/* + * The general form here is based on a "fast key erasure RNG" from + * . It generates a ChaCha + * block using the provided key, and then immediately overwites that + * key with half the block. It returns the resultant ChaCha state to the + * user, along with the second half of the block containing 32 bytes of + * random data that may be used; random_data_len may not be greater than + * 32. + */ +static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], + u32 chacha_state[CHACHA_STATE_WORDS], + u8 *random_data, size_t random_data_len) { - unsigned long flags, init_time; + u8 first_block[CHACHA_BLOCK_SIZE]; - if (crng_ready()) { - init_time = READ_ONCE(primary_crng.init_time); - if (time_after(jiffies, init_time + CRNG_RESEED_INTERVAL)) - crng_reseed(); - } - spin_lock_irqsave(&primary_crng.lock, flags); - chacha20_block(&primary_crng.state[0], out); - if (primary_crng.state[12] == 0) - primary_crng.state[13]++; - spin_unlock_irqrestore(&primary_crng.lock, flags); + BUG_ON(random_data_len > 32); + + chacha_init_consts(chacha_state); + memcpy(&chacha_state[4], key, CHACHA_KEY_SIZE); + memset(&chacha_state[12], 0, sizeof(u32) * 4); + chacha20_block(chacha_state, first_block); + + memcpy(key, first_block, CHACHA_KEY_SIZE); + memcpy(random_data, first_block + CHACHA_KEY_SIZE, random_data_len); + memzero_explicit(first_block, sizeof(first_block)); } /* - * Use the leftover bytes from the CRNG block output (if there is - * enough) to mutate the CRNG key to provide backtracking protection. + * This function returns a ChaCha state that you may use for generating + * random data. It also returns up to 32 bytes on its own of random data + * that may be used; random_data_len may not be greater than 32. */ -static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used) +static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], + u8 *random_data, size_t random_data_len) { unsigned long flags; - u32 *s, *d; - int i; + struct crng *crng; - used = round_up(used, sizeof(u32)); - if (used + CHACHA_KEY_SIZE > CHACHA_BLOCK_SIZE) { - extract_crng(tmp); - used = 0; + BUG_ON(random_data_len > 32); + + /* + * For the fast path, we check whether we're ready, unlocked first, and + * then re-check once locked later. In the case where we're really not + * ready, we do fast key erasure with the base_crng directly, because + * this is what crng_{fast,slow}_load mutate during early init. + */ + if (unlikely(!crng_ready())) { + bool ready; + + spin_lock_irqsave(&base_crng.lock, flags); + ready = crng_ready(); + if (!ready) + crng_fast_key_erasure(base_crng.key, chacha_state, + random_data, random_data_len); + spin_unlock_irqrestore(&base_crng.lock, flags); + if (!ready) + return; } - spin_lock_irqsave(&primary_crng.lock, flags); - s = (u32 *)&tmp[used]; - d = &primary_crng.state[4]; - for (i = 0; i < 8; i++) - *d++ ^= *s++; - spin_unlock_irqrestore(&primary_crng.lock, flags); + + /* + * If the base_crng is more than 5 minutes old, we reseed, which + * in turn bumps the generation counter that we check below. + */ + if (unlikely(time_after(jiffies, READ_ONCE(base_crng.birth) + CRNG_RESEED_INTERVAL))) + crng_reseed(); + + local_lock_irqsave(&crngs.lock, flags); + crng = raw_cpu_ptr(&crngs); + + /* + * If our per-cpu crng is older than the base_crng, then it means + * somebody reseeded the base_crng. In that case, we do fast key + * erasure on the base_crng, and use its output as the new key + * for our per-cpu crng. This brings us up to date with base_crng. + */ + if (unlikely(crng->generation != READ_ONCE(base_crng.generation))) { + spin_lock(&base_crng.lock); + crng_fast_key_erasure(base_crng.key, chacha_state, + crng->key, sizeof(crng->key)); + crng->generation = base_crng.generation; + spin_unlock(&base_crng.lock); + } + + /* + * Finally, when we've made it this far, our per-cpu crng has an up + * to date key, and we can do fast key erasure with it to produce + * some random data and a ChaCha state for the caller. All other + * branches of this function are "unlikely", so most of the time we + * should wind up here immediately. + */ + crng_fast_key_erasure(crng->key, chacha_state, random_data, random_data_len); + local_unlock_irqrestore(&crngs.lock, flags); } -static ssize_t extract_crng_user(void __user *buf, size_t nbytes) +static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) { - ssize_t ret = 0, i = CHACHA_BLOCK_SIZE; - u8 tmp[CHACHA_BLOCK_SIZE] __aligned(4); - int large_request = (nbytes > 256); + bool large_request = nbytes > 256; + ssize_t ret = 0, len; + u32 chacha_state[CHACHA_STATE_WORDS]; + u8 output[CHACHA_BLOCK_SIZE]; + + if (!nbytes) + return 0; + + len = min_t(ssize_t, 32, nbytes); + crng_make_state(chacha_state, output, len); + + if (copy_to_user(buf, output, len)) + return -EFAULT; + nbytes -= len; + buf += len; + ret += len; while (nbytes) { if (large_request && need_resched()) { - if (signal_pending(current)) { - if (ret == 0) - ret = -ERESTARTSYS; + if (signal_pending(current)) break; - } schedule(); } - extract_crng(tmp); - i = min_t(int, nbytes, CHACHA_BLOCK_SIZE); - if (copy_to_user(buf, tmp, i)) { + chacha20_block(chacha_state, output); + if (unlikely(chacha_state[12] == 0)) + ++chacha_state[13]; + + len = min_t(ssize_t, nbytes, CHACHA_BLOCK_SIZE); + if (copy_to_user(buf, output, len)) { ret = -EFAULT; break; } - nbytes -= i; - buf += i; - ret += i; + nbytes -= len; + buf += len; + ret += len; } - crng_backtrack_protect(tmp, i); - - /* Wipe data just written to memory */ - memzero_explicit(tmp, sizeof(tmp)); + memzero_explicit(chacha_state, sizeof(chacha_state)); + memzero_explicit(output, sizeof(output)); return ret; } @@ -976,23 +1016,36 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller, void */ static void _get_random_bytes(void *buf, int nbytes) { - u8 tmp[CHACHA_BLOCK_SIZE] __aligned(4); + u32 chacha_state[CHACHA_STATE_WORDS]; + u8 tmp[CHACHA_BLOCK_SIZE]; + ssize_t len; trace_get_random_bytes(nbytes, _RET_IP_); - while (nbytes >= CHACHA_BLOCK_SIZE) { - extract_crng(buf); - buf += CHACHA_BLOCK_SIZE; + if (!nbytes) + return; + + len = min_t(ssize_t, 32, nbytes); + crng_make_state(chacha_state, buf, len); + nbytes -= len; + buf += len; + + while (nbytes) { + if (nbytes < CHACHA_BLOCK_SIZE) { + chacha20_block(chacha_state, tmp); + memcpy(buf, tmp, nbytes); + memzero_explicit(tmp, sizeof(tmp)); + break; + } + + chacha20_block(chacha_state, buf); + if (unlikely(chacha_state[12] == 0)) + ++chacha_state[13]; nbytes -= CHACHA_BLOCK_SIZE; + buf += CHACHA_BLOCK_SIZE; } - if (nbytes > 0) { - extract_crng(tmp); - memcpy(buf, tmp, nbytes); - crng_backtrack_protect(tmp, nbytes); - } else - crng_backtrack_protect(tmp, CHACHA_BLOCK_SIZE); - memzero_explicit(tmp, sizeof(tmp)); + memzero_explicit(chacha_state, sizeof(chacha_state)); } void get_random_bytes(void *buf, int nbytes) @@ -1223,13 +1276,12 @@ int __init rand_initialize(void) mix_pool_bytes(&now, sizeof(now)); mix_pool_bytes(utsname(), sizeof(*(utsname()))); - extract_entropy(&primary_crng.state[4], sizeof(u32) * 12); + extract_entropy(base_crng.key, sizeof(base_crng.key)); if (arch_init && trust_cpu && crng_init < 2) { invalidate_batched_entropy(); crng_init = 2; pr_notice("crng init done (trusting CPU's manufacturer)\n"); } - primary_crng.init_time = jiffies - CRNG_RESEED_INTERVAL - 1; if (ratelimit_disable) { urandom_warning.interval = 0; @@ -1261,7 +1313,7 @@ static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, int ret; nbytes = min_t(size_t, nbytes, INT_MAX >> 6); - ret = extract_crng_user(buf, nbytes); + ret = get_random_bytes_user(buf, nbytes); trace_urandom_read(8 * nbytes, 0, input_pool.entropy_count); return ret; } @@ -1577,8 +1629,15 @@ static atomic_t batch_generation = ATOMIC_INIT(0); struct batched_entropy { union { - u64 entropy_u64[CHACHA_BLOCK_SIZE / sizeof(u64)]; - u32 entropy_u32[CHACHA_BLOCK_SIZE / sizeof(u32)]; + /* + * We make this 1.5x a ChaCha block, so that we get the + * remaining 32 bytes from fast key erasure, plus one full + * block from the detached ChaCha state. We can increase + * the size of this later if needed so long as we keep the + * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. + */ + u64 entropy_u64[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u64))]; + u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))]; }; local_lock_t lock; unsigned int position; @@ -1587,14 +1646,13 @@ struct batched_entropy { /* * Get a random word for internal kernel use only. The quality of the random - * number is good as /dev/urandom, but there is no backtrack protection, with - * the goal of being quite fast and not depleting entropy. In order to ensure - * that the randomness provided by this function is okay, the function - * wait_for_random_bytes() should be called and return 0 at least once at any - * point prior. + * number is good as /dev/urandom. In order to ensure that the randomness + * provided by this function is okay, the function wait_for_random_bytes() + * should be called and return 0 at least once at any point prior. */ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = { - .lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock) + .lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock), + .position = UINT_MAX }; u64 get_random_u64(void) @@ -1611,21 +1669,24 @@ u64 get_random_u64(void) batch = raw_cpu_ptr(&batched_entropy_u64); next_gen = atomic_read(&batch_generation); - if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0 || + if (batch->position >= ARRAY_SIZE(batch->entropy_u64) || next_gen != batch->generation) { - extract_crng((u8 *)batch->entropy_u64); + _get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64)); batch->position = 0; batch->generation = next_gen; } - ret = batch->entropy_u64[batch->position++]; + ret = batch->entropy_u64[batch->position]; + batch->entropy_u64[batch->position] = 0; + ++batch->position; local_unlock_irqrestore(&batched_entropy_u64.lock, flags); return ret; } EXPORT_SYMBOL(get_random_u64); static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = { - .lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock) + .lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock), + .position = UINT_MAX }; u32 get_random_u32(void) @@ -1642,14 +1703,16 @@ u32 get_random_u32(void) batch = raw_cpu_ptr(&batched_entropy_u32); next_gen = atomic_read(&batch_generation); - if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0 || + if (batch->position >= ARRAY_SIZE(batch->entropy_u32) || next_gen != batch->generation) { - extract_crng((u8 *)batch->entropy_u32); + _get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32)); batch->position = 0; batch->generation = next_gen; } - ret = batch->entropy_u32[batch->position++]; + ret = batch->entropy_u32[batch->position]; + batch->entropy_u32[batch->position] = 0; + ++batch->position; local_unlock_irqrestore(&batched_entropy_u32.lock, flags); return ret; } -- cgit v1.2.3 From 66e4c2b9541503d721e936cc3898c9f25f4591ff Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Feb 2022 19:23:17 +0100 Subject: random: use hash function for crng_slow_load() Since we have a hash function that's really fast, and the goal of crng_slow_load() is reportedly to "touch all of the crng's state", we can just hash the old state together with the new state and call it a day. This way we dont need to reason about another LFSR or worry about various attacks there. This code is only ever used at early boot and then never again. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 42 +++++++++++++++--------------------------- 1 file changed, 15 insertions(+), 27 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 538eaa469f5e..630b9b9e7d25 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -477,42 +477,30 @@ static size_t crng_fast_load(const u8 *cp, size_t len) * all), and (2) it doesn't have the performance constraints of * crng_fast_load(). * - * So we do something more comprehensive which is guaranteed to touch - * all of the primary_crng's state, and which uses a LFSR with a - * period of 255 as part of the mixing algorithm. Finally, we do - * *not* advance crng_init_cnt since buffer we may get may be something - * like a fixed DMI table (for example), which might very well be - * unique to the machine, but is otherwise unvarying. + * So, we simply hash the contents in with the current key. Finally, + * we do *not* advance crng_init_cnt since buffer we may get may be + * something like a fixed DMI table (for example), which might very + * well be unique to the machine, but is otherwise unvarying. */ -static int crng_slow_load(const u8 *cp, size_t len) +static void crng_slow_load(const u8 *cp, size_t len) { unsigned long flags; - static u8 lfsr = 1; - u8 tmp; - unsigned int i, max = sizeof(base_crng.key); - const u8 *src_buf = cp; - u8 *dest_buf = base_crng.key; + struct blake2s_state hash; + + blake2s_init(&hash, sizeof(base_crng.key)); if (!spin_trylock_irqsave(&base_crng.lock, flags)) - return 0; + return; if (crng_init != 0) { spin_unlock_irqrestore(&base_crng.lock, flags); - return 0; - } - if (len > max) - max = len; - - for (i = 0; i < max; i++) { - tmp = lfsr; - lfsr >>= 1; - if (tmp & 1) - lfsr ^= 0xE1; - tmp = dest_buf[i % sizeof(base_crng.key)]; - dest_buf[i % sizeof(base_crng.key)] ^= src_buf[i % len] ^ lfsr; - lfsr += (tmp << 3) | (tmp >> 5); + return; } + + blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); + blake2s_update(&hash, cp, len); + blake2s_final(&hash, base_crng.key); + spin_unlock_irqrestore(&base_crng.lock, flags); - return 1; } static void crng_reseed(void) -- cgit v1.2.3 From 04ec96b768c9dd43946b047c3da60dcc66431370 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 9 Feb 2022 14:43:25 +0100 Subject: random: make more consistent use of integer types We've been using a flurry of int, unsigned int, size_t, and ssize_t. Let's unify all of this into size_t where it makes sense, as it does in most places, and leave ssize_t for return values with possible errors. In addition, keeping with the convention of other functions in this file, functions that are dealing with raw bytes now take void * consistently instead of a mix of that and u8 *, because much of the time we're actually passing some other structure that is then interpreted as bytes by the function. We also take the opportunity to fix the outdated and incorrect comment in get_random_bytes_arch(). Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Jann Horn Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 123 +++++++++++++++++++----------------------- include/linux/hw_random.h | 2 +- include/linux/random.h | 10 ++-- include/trace/events/random.h | 79 +++++++++++++-------------- 4 files changed, 99 insertions(+), 115 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 630b9b9e7d25..768dee5e081a 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -69,7 +69,7 @@ * * The primary kernel interfaces are: * - * void get_random_bytes(void *buf, int nbytes); + * void get_random_bytes(void *buf, size_t nbytes); * u32 get_random_u32() * u64 get_random_u64() * unsigned int get_random_int() @@ -97,14 +97,14 @@ * The current exported interfaces for gathering environmental noise * from the devices are: * - * void add_device_randomness(const void *buf, unsigned int size); + * void add_device_randomness(const void *buf, size_t size); * void add_input_randomness(unsigned int type, unsigned int code, * unsigned int value); * void add_interrupt_randomness(int irq); * void add_disk_randomness(struct gendisk *disk); - * void add_hwgenerator_randomness(const char *buffer, size_t count, + * void add_hwgenerator_randomness(const void *buffer, size_t count, * size_t entropy); - * void add_bootloader_randomness(const void *buf, unsigned int size); + * void add_bootloader_randomness(const void *buf, size_t size); * * add_device_randomness() is for adding data to the random pool that * is likely to differ between two devices (or possibly even per boot). @@ -268,7 +268,7 @@ static int crng_init = 0; #define crng_ready() (likely(crng_init > 1)) static int crng_init_cnt = 0; static void process_random_ready_list(void); -static void _get_random_bytes(void *buf, int nbytes); +static void _get_random_bytes(void *buf, size_t nbytes); static struct ratelimit_state unseeded_warning = RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3); @@ -290,7 +290,7 @@ MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression"); static struct { struct blake2s_state hash; spinlock_t lock; - int entropy_count; + unsigned int entropy_count; } input_pool = { .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE), BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4, @@ -308,18 +308,12 @@ static void crng_reseed(void); * update the entropy estimate. The caller should call * credit_entropy_bits if this is appropriate. */ -static void _mix_pool_bytes(const void *in, int nbytes) +static void _mix_pool_bytes(const void *in, size_t nbytes) { blake2s_update(&input_pool.hash, in, nbytes); } -static void __mix_pool_bytes(const void *in, int nbytes) -{ - trace_mix_pool_bytes_nolock(nbytes, _RET_IP_); - _mix_pool_bytes(in, nbytes); -} - -static void mix_pool_bytes(const void *in, int nbytes) +static void mix_pool_bytes(const void *in, size_t nbytes) { unsigned long flags; @@ -383,18 +377,18 @@ static void process_random_ready_list(void) spin_unlock_irqrestore(&random_ready_list_lock, flags); } -static void credit_entropy_bits(int nbits) +static void credit_entropy_bits(size_t nbits) { - int entropy_count, orig; + unsigned int entropy_count, orig, add; - if (nbits <= 0) + if (!nbits) return; - nbits = min(nbits, POOL_BITS); + add = min_t(size_t, nbits, POOL_BITS); do { orig = READ_ONCE(input_pool.entropy_count); - entropy_count = min(POOL_BITS, orig + nbits); + entropy_count = min_t(unsigned int, POOL_BITS, orig + add); } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); trace_credit_entropy_bits(nbits, entropy_count, _RET_IP_); @@ -443,10 +437,10 @@ static void invalidate_batched_entropy(void); * path. So we can't afford to dilly-dally. Returns the number of * bytes processed from cp. */ -static size_t crng_fast_load(const u8 *cp, size_t len) +static size_t crng_fast_load(const void *cp, size_t len) { unsigned long flags; - u8 *p; + const u8 *src = (const u8 *)cp; size_t ret = 0; if (!spin_trylock_irqsave(&base_crng.lock, flags)) @@ -455,10 +449,9 @@ static size_t crng_fast_load(const u8 *cp, size_t len) spin_unlock_irqrestore(&base_crng.lock, flags); return 0; } - p = base_crng.key; while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) { - p[crng_init_cnt % sizeof(base_crng.key)] ^= *cp; - cp++; crng_init_cnt++; len--; ret++; + base_crng.key[crng_init_cnt % sizeof(base_crng.key)] ^= *src; + src++; crng_init_cnt++; len--; ret++; } if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { invalidate_batched_entropy(); @@ -482,7 +475,7 @@ static size_t crng_fast_load(const u8 *cp, size_t len) * something like a fixed DMI table (for example), which might very * well be unique to the machine, but is otherwise unvarying. */ -static void crng_slow_load(const u8 *cp, size_t len) +static void crng_slow_load(const void *cp, size_t len) { unsigned long flags; struct blake2s_state hash; @@ -656,14 +649,15 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) { bool large_request = nbytes > 256; - ssize_t ret = 0, len; + ssize_t ret = 0; + size_t len; u32 chacha_state[CHACHA_STATE_WORDS]; u8 output[CHACHA_BLOCK_SIZE]; if (!nbytes) return 0; - len = min_t(ssize_t, 32, nbytes); + len = min_t(size_t, 32, nbytes); crng_make_state(chacha_state, output, len); if (copy_to_user(buf, output, len)) @@ -683,7 +677,7 @@ static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) if (unlikely(chacha_state[12] == 0)) ++chacha_state[13]; - len = min_t(ssize_t, nbytes, CHACHA_BLOCK_SIZE); + len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE); if (copy_to_user(buf, output, len)) { ret = -EFAULT; break; @@ -721,7 +715,7 @@ struct timer_rand_state { * the entropy pool having similar initial state across largely * identical devices. */ -void add_device_randomness(const void *buf, unsigned int size) +void add_device_randomness(const void *buf, size_t size) { unsigned long time = random_get_entropy() ^ jiffies; unsigned long flags; @@ -749,7 +743,7 @@ static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE; * keyboard scan codes, and 256 upwards for interrupts. * */ -static void add_timer_randomness(struct timer_rand_state *state, unsigned num) +static void add_timer_randomness(struct timer_rand_state *state, unsigned int num) { struct { long jiffies; @@ -793,7 +787,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num) * Round down by 1 bit on general principles, * and limit entropy estimate to 12 bits. */ - credit_entropy_bits(min_t(int, fls(delta >> 1), 11)); + credit_entropy_bits(min_t(unsigned int, fls(delta >> 1), 11)); } void add_input_randomness(unsigned int type, unsigned int code, @@ -874,8 +868,8 @@ void add_interrupt_randomness(int irq) add_interrupt_bench(cycles); if (unlikely(crng_init == 0)) { - if ((fast_pool->count >= 64) && - crng_fast_load((u8 *)fast_pool->pool, sizeof(fast_pool->pool)) > 0) { + if (fast_pool->count >= 64 && + crng_fast_load(fast_pool->pool, sizeof(fast_pool->pool)) > 0) { fast_pool->count = 0; fast_pool->last = now; if (spin_trylock(&input_pool.lock)) { @@ -893,7 +887,7 @@ void add_interrupt_randomness(int irq) return; fast_pool->last = now; - __mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool)); + _mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool)); spin_unlock(&input_pool.lock); fast_pool->count = 0; @@ -1002,18 +996,18 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller, void * wait_for_random_bytes() should be called and return 0 at least once * at any point prior. */ -static void _get_random_bytes(void *buf, int nbytes) +static void _get_random_bytes(void *buf, size_t nbytes) { u32 chacha_state[CHACHA_STATE_WORDS]; u8 tmp[CHACHA_BLOCK_SIZE]; - ssize_t len; + size_t len; trace_get_random_bytes(nbytes, _RET_IP_); if (!nbytes) return; - len = min_t(ssize_t, 32, nbytes); + len = min_t(size_t, 32, nbytes); crng_make_state(chacha_state, buf, len); nbytes -= len; buf += len; @@ -1036,7 +1030,7 @@ static void _get_random_bytes(void *buf, int nbytes) memzero_explicit(chacha_state, sizeof(chacha_state)); } -void get_random_bytes(void *buf, int nbytes) +void get_random_bytes(void *buf, size_t nbytes) { static void *previous; @@ -1197,25 +1191,19 @@ EXPORT_SYMBOL(del_random_ready_callback); /* * This function will use the architecture-specific hardware random - * number generator if it is available. The arch-specific hw RNG will - * almost certainly be faster than what we can do in software, but it - * is impossible to verify that it is implemented securely (as - * opposed, to, say, the AES encryption of a sequence number using a - * key known by the NSA). So it's useful if we need the speed, but - * only if we're willing to trust the hardware manufacturer not to - * have put in a back door. - * - * Return number of bytes filled in. + * number generator if it is available. It is not recommended for + * use. Use get_random_bytes() instead. It returns the number of + * bytes filled in. */ -int __must_check get_random_bytes_arch(void *buf, int nbytes) +size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes) { - int left = nbytes; + size_t left = nbytes; u8 *p = buf; trace_get_random_bytes_arch(left, _RET_IP_); while (left) { unsigned long v; - int chunk = min_t(int, left, sizeof(unsigned long)); + size_t chunk = min_t(size_t, left, sizeof(unsigned long)); if (!arch_get_random_long(&v)) break; @@ -1248,12 +1236,12 @@ early_param("random.trust_cpu", parse_trust_cpu); */ int __init rand_initialize(void) { - int i; + size_t i; ktime_t now = ktime_get_real(); bool arch_init = true; unsigned long rv; - for (i = BLAKE2S_BLOCK_SIZE; i > 0; i -= sizeof(rv)) { + for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) { if (!arch_get_random_seed_long_early(&rv) && !arch_get_random_long_early(&rv)) { rv = random_get_entropy(); @@ -1302,7 +1290,7 @@ static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, nbytes = min_t(size_t, nbytes, INT_MAX >> 6); ret = get_random_bytes_user(buf, nbytes); - trace_urandom_read(8 * nbytes, 0, input_pool.entropy_count); + trace_urandom_read(nbytes, input_pool.entropy_count); return ret; } @@ -1346,19 +1334,18 @@ static __poll_t random_poll(struct file *file, poll_table *wait) return mask; } -static int write_pool(const char __user *buffer, size_t count) +static int write_pool(const char __user *ubuf, size_t count) { - size_t bytes; - u8 buf[BLAKE2S_BLOCK_SIZE]; - const char __user *p = buffer; + size_t len; + u8 block[BLAKE2S_BLOCK_SIZE]; - while (count > 0) { - bytes = min(count, sizeof(buf)); - if (copy_from_user(buf, p, bytes)) + while (count) { + len = min(count, sizeof(block)); + if (copy_from_user(block, ubuf, len)) return -EFAULT; - count -= bytes; - p += bytes; - mix_pool_bytes(buf, bytes); + count -= len; + ubuf += len; + mix_pool_bytes(block, len); cond_resched(); } @@ -1368,7 +1355,7 @@ static int write_pool(const char __user *buffer, size_t count) static ssize_t random_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos) { - size_t ret; + int ret; ret = write_pool(buffer, count); if (ret) @@ -1464,8 +1451,6 @@ const struct file_operations urandom_fops = { SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, flags) { - int ret; - if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)) return -EINVAL; @@ -1480,6 +1465,8 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, count = INT_MAX; if (!(flags & GRND_INSECURE) && !crng_ready()) { + int ret; + if (flags & GRND_NONBLOCK) return -EAGAIN; ret = wait_for_random_bytes(); @@ -1751,7 +1738,7 @@ unsigned long randomize_page(unsigned long start, unsigned long range) * Those devices may produce endless random bits and will be throttled * when our pool is full. */ -void add_hwgenerator_randomness(const char *buffer, size_t count, +void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy) { if (unlikely(crng_init == 0)) { @@ -1782,7 +1769,7 @@ EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); * it would be regarded as device data. * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER. */ -void add_bootloader_randomness(const void *buf, unsigned int size) +void add_bootloader_randomness(const void *buf, size_t size) { if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER)) add_hwgenerator_randomness(buf, size, size * 8); diff --git a/include/linux/hw_random.h b/include/linux/hw_random.h index 8e6dd908da21..1a9fc38f8938 100644 --- a/include/linux/hw_random.h +++ b/include/linux/hw_random.h @@ -61,6 +61,6 @@ extern int devm_hwrng_register(struct device *dev, struct hwrng *rng); extern void hwrng_unregister(struct hwrng *rng); extern void devm_hwrng_unregister(struct device *dve, struct hwrng *rng); /** Feed random bits into the pool. */ -extern void add_hwgenerator_randomness(const char *buffer, size_t count, size_t entropy); +extern void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy); #endif /* LINUX_HWRANDOM_H_ */ diff --git a/include/linux/random.h b/include/linux/random.h index c45b2693e51f..e92efb39779c 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -20,8 +20,8 @@ struct random_ready_callback { struct module *owner; }; -extern void add_device_randomness(const void *, unsigned int); -extern void add_bootloader_randomness(const void *, unsigned int); +extern void add_device_randomness(const void *, size_t); +extern void add_bootloader_randomness(const void *, size_t); #if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__) static inline void add_latent_entropy(void) @@ -37,13 +37,13 @@ extern void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) __latent_entropy; extern void add_interrupt_randomness(int irq) __latent_entropy; -extern void get_random_bytes(void *buf, int nbytes); +extern void get_random_bytes(void *buf, size_t nbytes); extern int wait_for_random_bytes(void); extern int __init rand_initialize(void); extern bool rng_is_initialized(void); extern int add_random_ready_callback(struct random_ready_callback *rdy); extern void del_random_ready_callback(struct random_ready_callback *rdy); -extern int __must_check get_random_bytes_arch(void *buf, int nbytes); +extern size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes); #ifndef MODULE extern const struct file_operations random_fops, urandom_fops; @@ -87,7 +87,7 @@ static inline unsigned long get_random_canary(void) /* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes). * Returns the result of the call to wait_for_random_bytes. */ -static inline int get_random_bytes_wait(void *buf, int nbytes) +static inline int get_random_bytes_wait(void *buf, size_t nbytes) { int ret = wait_for_random_bytes(); get_random_bytes(buf, nbytes); diff --git a/include/trace/events/random.h b/include/trace/events/random.h index ad149aeaf42c..0609a2810a12 100644 --- a/include/trace/events/random.h +++ b/include/trace/events/random.h @@ -9,13 +9,13 @@ #include TRACE_EVENT(add_device_randomness, - TP_PROTO(int bytes, unsigned long IP), + TP_PROTO(size_t bytes, unsigned long IP), TP_ARGS(bytes, IP), TP_STRUCT__entry( - __field( int, bytes ) - __field(unsigned long, IP ) + __field(size_t, bytes ) + __field(unsigned long, IP ) ), TP_fast_assign( @@ -23,18 +23,18 @@ TRACE_EVENT(add_device_randomness, __entry->IP = IP; ), - TP_printk("bytes %d caller %pS", + TP_printk("bytes %zu caller %pS", __entry->bytes, (void *)__entry->IP) ); DECLARE_EVENT_CLASS(random__mix_pool_bytes, - TP_PROTO(int bytes, unsigned long IP), + TP_PROTO(size_t bytes, unsigned long IP), TP_ARGS(bytes, IP), TP_STRUCT__entry( - __field( int, bytes ) - __field(unsigned long, IP ) + __field(size_t, bytes ) + __field(unsigned long, IP ) ), TP_fast_assign( @@ -42,12 +42,12 @@ DECLARE_EVENT_CLASS(random__mix_pool_bytes, __entry->IP = IP; ), - TP_printk("input pool: bytes %d caller %pS", + TP_printk("input pool: bytes %zu caller %pS", __entry->bytes, (void *)__entry->IP) ); DEFINE_EVENT(random__mix_pool_bytes, mix_pool_bytes, - TP_PROTO(int bytes, unsigned long IP), + TP_PROTO(size_t bytes, unsigned long IP), TP_ARGS(bytes, IP) ); @@ -59,13 +59,13 @@ DEFINE_EVENT(random__mix_pool_bytes, mix_pool_bytes_nolock, ); TRACE_EVENT(credit_entropy_bits, - TP_PROTO(int bits, int entropy_count, unsigned long IP), + TP_PROTO(size_t bits, size_t entropy_count, unsigned long IP), TP_ARGS(bits, entropy_count, IP), TP_STRUCT__entry( - __field( int, bits ) - __field( int, entropy_count ) + __field(size_t, bits ) + __field(size_t, entropy_count ) __field(unsigned long, IP ) ), @@ -75,34 +75,34 @@ TRACE_EVENT(credit_entropy_bits, __entry->IP = IP; ), - TP_printk("input pool: bits %d entropy_count %d caller %pS", + TP_printk("input pool: bits %zu entropy_count %zu caller %pS", __entry->bits, __entry->entropy_count, (void *)__entry->IP) ); TRACE_EVENT(add_input_randomness, - TP_PROTO(int input_bits), + TP_PROTO(size_t input_bits), TP_ARGS(input_bits), TP_STRUCT__entry( - __field( int, input_bits ) + __field(size_t, input_bits ) ), TP_fast_assign( __entry->input_bits = input_bits; ), - TP_printk("input_pool_bits %d", __entry->input_bits) + TP_printk("input_pool_bits %zu", __entry->input_bits) ); TRACE_EVENT(add_disk_randomness, - TP_PROTO(dev_t dev, int input_bits), + TP_PROTO(dev_t dev, size_t input_bits), TP_ARGS(dev, input_bits), TP_STRUCT__entry( - __field( dev_t, dev ) - __field( int, input_bits ) + __field(dev_t, dev ) + __field(size_t, input_bits ) ), TP_fast_assign( @@ -110,17 +110,17 @@ TRACE_EVENT(add_disk_randomness, __entry->input_bits = input_bits; ), - TP_printk("dev %d,%d input_pool_bits %d", MAJOR(__entry->dev), + TP_printk("dev %d,%d input_pool_bits %zu", MAJOR(__entry->dev), MINOR(__entry->dev), __entry->input_bits) ); DECLARE_EVENT_CLASS(random__get_random_bytes, - TP_PROTO(int nbytes, unsigned long IP), + TP_PROTO(size_t nbytes, unsigned long IP), TP_ARGS(nbytes, IP), TP_STRUCT__entry( - __field( int, nbytes ) + __field(size_t, nbytes ) __field(unsigned long, IP ) ), @@ -129,29 +129,29 @@ DECLARE_EVENT_CLASS(random__get_random_bytes, __entry->IP = IP; ), - TP_printk("nbytes %d caller %pS", __entry->nbytes, (void *)__entry->IP) + TP_printk("nbytes %zu caller %pS", __entry->nbytes, (void *)__entry->IP) ); DEFINE_EVENT(random__get_random_bytes, get_random_bytes, - TP_PROTO(int nbytes, unsigned long IP), + TP_PROTO(size_t nbytes, unsigned long IP), TP_ARGS(nbytes, IP) ); DEFINE_EVENT(random__get_random_bytes, get_random_bytes_arch, - TP_PROTO(int nbytes, unsigned long IP), + TP_PROTO(size_t nbytes, unsigned long IP), TP_ARGS(nbytes, IP) ); DECLARE_EVENT_CLASS(random__extract_entropy, - TP_PROTO(int nbytes, int entropy_count), + TP_PROTO(size_t nbytes, size_t entropy_count), TP_ARGS(nbytes, entropy_count), TP_STRUCT__entry( - __field( int, nbytes ) - __field( int, entropy_count ) + __field( size_t, nbytes ) + __field( size_t, entropy_count ) ), TP_fast_assign( @@ -159,37 +159,34 @@ DECLARE_EVENT_CLASS(random__extract_entropy, __entry->entropy_count = entropy_count; ), - TP_printk("input pool: nbytes %d entropy_count %d", + TP_printk("input pool: nbytes %zu entropy_count %zu", __entry->nbytes, __entry->entropy_count) ); DEFINE_EVENT(random__extract_entropy, extract_entropy, - TP_PROTO(int nbytes, int entropy_count), + TP_PROTO(size_t nbytes, size_t entropy_count), TP_ARGS(nbytes, entropy_count) ); TRACE_EVENT(urandom_read, - TP_PROTO(int got_bits, int pool_left, int input_left), + TP_PROTO(size_t nbytes, size_t entropy_count), - TP_ARGS(got_bits, pool_left, input_left), + TP_ARGS(nbytes, entropy_count), TP_STRUCT__entry( - __field( int, got_bits ) - __field( int, pool_left ) - __field( int, input_left ) + __field( size_t, nbytes ) + __field( size_t, entropy_count ) ), TP_fast_assign( - __entry->got_bits = got_bits; - __entry->pool_left = pool_left; - __entry->input_left = input_left; + __entry->nbytes = nbytes; + __entry->entropy_count = entropy_count; ), - TP_printk("got_bits %d nonblocking_pool_entropy_left %d " - "input_entropy_left %d", __entry->got_bits, - __entry->pool_left, __entry->input_left) + TP_printk("reading: nbytes %zu entropy_count %zu", + __entry->nbytes, __entry->entropy_count) ); TRACE_EVENT(prandom_u32, -- cgit v1.2.3 From 434537ae54ad37e93555de21b6ac8133d6d773a9 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Mon, 7 Feb 2022 23:37:13 +0100 Subject: random: remove outdated INT_MAX >> 6 check in urandom_read() In 79a8468747c5 ("random: check for increase of entropy_count because of signed conversion"), a number of checks were added around what values were passed to account(), because account() was doing fancy fixed point fractional arithmetic, and a user had some ability to pass large values directly into it. One of things in that commit was limiting those values to INT_MAX >> 6. The first >> 3 was for bytes to bits, and the next >> 3 was for bits to 1/8 fractional bits. However, for several years now, urandom reads no longer touch entropy accounting, and so this check serves no purpose. The current flow is: urandom_read_nowarn()-->get_random_bytes_user()-->chacha20_block() Of course, we don't want that size_t to be truncated when adding it into the ssize_t. But we arrive at urandom_read_nowarn() in the first place either via ordinary fops, which limits reads to MAX_RW_COUNT, or via getrandom() which limits reads to INT_MAX. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Jann Horn Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 768dee5e081a..896ec54f8f5c 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1286,9 +1286,8 @@ void rand_initialize_disk(struct gendisk *disk) static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { - int ret; + ssize_t ret; - nbytes = min_t(size_t, nbytes, INT_MAX >> 6); ret = get_random_bytes_user(buf, nbytes); trace_urandom_read(nbytes, input_pool.entropy_count); return ret; -- cgit v1.2.3 From 7b5164fb1279bf0251371848e40bae646b59b3a8 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 9 Feb 2022 18:42:13 +0100 Subject: random: zero buffer after reading entropy from userspace This buffer may contain entropic data that shouldn't stick around longer than needed, so zero out the temporary buffer at the end of write_pool(). Reviewed-by: Dominik Brodowski Reviewed-by: Jann Horn Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 896ec54f8f5c..8ae7d0b30280 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1336,19 +1336,24 @@ static __poll_t random_poll(struct file *file, poll_table *wait) static int write_pool(const char __user *ubuf, size_t count) { size_t len; + int ret = 0; u8 block[BLAKE2S_BLOCK_SIZE]; while (count) { len = min(count, sizeof(block)); - if (copy_from_user(block, ubuf, len)) - return -EFAULT; + if (copy_from_user(block, ubuf, len)) { + ret = -EFAULT; + goto out; + } count -= len; ubuf += len; mix_pool_bytes(block, len); cond_resched(); } - return 0; +out: + memzero_explicit(block, sizeof(block)); + return ret; } static ssize_t random_write(struct file *file, const char __user *buffer, -- cgit v1.2.3 From 7191c628fe07b70d3f37de736d173d1b115396ed Mon Sep 17 00:00:00 2001 From: Dominik Brodowski Date: Wed, 9 Feb 2022 19:57:06 +0100 Subject: random: fix locking for crng_init in crng_reseed() crng_init is protected by primary_crng->lock. Therefore, we need to hold this lock when increasing crng_init to 2. As we shouldn't hold this lock for too long, only hold it for those parts which require protection. Signed-off-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 8ae7d0b30280..1ccd92efa8f4 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -502,6 +502,7 @@ static void crng_reseed(void) int entropy_count; unsigned long next_gen; u8 key[CHACHA_KEY_SIZE]; + bool finalize_init = false; /* * First we make sure we have POOL_MIN_BITS of entropy in the pool, @@ -529,12 +530,14 @@ static void crng_reseed(void) ++next_gen; WRITE_ONCE(base_crng.generation, next_gen); WRITE_ONCE(base_crng.birth, jiffies); - spin_unlock_irqrestore(&base_crng.lock, flags); - memzero_explicit(key, sizeof(key)); - if (crng_init < 2) { invalidate_batched_entropy(); crng_init = 2; + finalize_init = true; + } + spin_unlock_irqrestore(&base_crng.lock, flags); + memzero_explicit(key, sizeof(key)); + if (finalize_init) { process_random_ready_list(); wake_up_interruptible(&crng_init_wait); kill_fasync(&fasync, SIGIO, POLL_IN); -- cgit v1.2.3 From 0791e8b655cc373718f0f58800fdc625a3447ac5 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 9 Feb 2022 22:46:48 +0100 Subject: random: tie batched entropy generation to base_crng generation Now that we have an explicit base_crng generation counter, we don't need a separate one for batched entropy. Rather, we can just move the generation forward every time we change crng_init state or update the base_crng key. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 29 ++++++++--------------------- 1 file changed, 8 insertions(+), 21 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 1ccd92efa8f4..c27ebf707380 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -430,8 +430,6 @@ static DEFINE_PER_CPU(struct crng, crngs) = { static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); -static void invalidate_batched_entropy(void); - /* * crng_fast_load() can be called by code in the interrupt service * path. So we can't afford to dilly-dally. Returns the number of @@ -454,7 +452,7 @@ static size_t crng_fast_load(const void *cp, size_t len) src++; crng_init_cnt++; len--; ret++; } if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { - invalidate_batched_entropy(); + ++base_crng.generation; crng_init = 1; } spin_unlock_irqrestore(&base_crng.lock, flags); @@ -531,7 +529,6 @@ static void crng_reseed(void) WRITE_ONCE(base_crng.generation, next_gen); WRITE_ONCE(base_crng.birth, jiffies); if (crng_init < 2) { - invalidate_batched_entropy(); crng_init = 2; finalize_init = true; } @@ -1256,8 +1253,9 @@ int __init rand_initialize(void) mix_pool_bytes(utsname(), sizeof(*(utsname()))); extract_entropy(base_crng.key, sizeof(base_crng.key)); + ++base_crng.generation; + if (arch_init && trust_cpu && crng_init < 2) { - invalidate_batched_entropy(); crng_init = 2; pr_notice("crng init done (trusting CPU's manufacturer)\n"); } @@ -1607,8 +1605,6 @@ static int __init random_sysctls_init(void) device_initcall(random_sysctls_init); #endif /* CONFIG_SYSCTL */ -static atomic_t batch_generation = ATOMIC_INIT(0); - struct batched_entropy { union { /* @@ -1622,8 +1618,8 @@ struct batched_entropy { u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))]; }; local_lock_t lock; + unsigned long generation; unsigned int position; - int generation; }; /* @@ -1643,14 +1639,14 @@ u64 get_random_u64(void) unsigned long flags; struct batched_entropy *batch; static void *previous; - int next_gen; + unsigned long next_gen; warn_unseeded_randomness(&previous); local_lock_irqsave(&batched_entropy_u64.lock, flags); batch = raw_cpu_ptr(&batched_entropy_u64); - next_gen = atomic_read(&batch_generation); + next_gen = READ_ONCE(base_crng.generation); if (batch->position >= ARRAY_SIZE(batch->entropy_u64) || next_gen != batch->generation) { _get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64)); @@ -1677,14 +1673,14 @@ u32 get_random_u32(void) unsigned long flags; struct batched_entropy *batch; static void *previous; - int next_gen; + unsigned long next_gen; warn_unseeded_randomness(&previous); local_lock_irqsave(&batched_entropy_u32.lock, flags); batch = raw_cpu_ptr(&batched_entropy_u32); - next_gen = atomic_read(&batch_generation); + next_gen = READ_ONCE(base_crng.generation); if (batch->position >= ARRAY_SIZE(batch->entropy_u32) || next_gen != batch->generation) { _get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32)); @@ -1700,15 +1696,6 @@ u32 get_random_u32(void) } EXPORT_SYMBOL(get_random_u32); -/* It's important to invalidate all potential batched entropy that might - * be stored before the crng is initialized, which we can do lazily by - * bumping the generation counter. - */ -static void invalidate_batched_entropy(void) -{ - atomic_inc(&batch_generation); -} - /** * randomize_page - Generate a random, page aligned address * @start: The smallest acceptable address the caller will take. -- cgit v1.2.3 From 95e6060c20a7f5db60163274c5222a725ac118f9 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 10 Feb 2022 16:35:24 +0100 Subject: random: remove ifdef'd out interrupt bench With tools like kbench9000 giving more finegrained responses, and this basically never having been used ever since it was initially added, let's just get rid of this. There *is* still work to be done on the interrupt handler, but this really isn't the way it's being developed. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- Documentation/admin-guide/sysctl/kernel.rst | 9 ------- drivers/char/random.c | 40 ----------------------------- 2 files changed, 49 deletions(-) diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index d3c6d9a501a9..5dd660aac0ae 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -1041,15 +1041,6 @@ This is a directory, with the following entries: are woken up. This file is writable for compatibility purposes, but writing to it has no effect on any RNG behavior. -If ``drivers/char/random.c`` is built with ``ADD_INTERRUPT_BENCH`` -defined, these additional entries are present: - -* ``add_interrupt_avg_cycles``: the average number of cycles between - interrupts used to feed the pool; - -* ``add_interrupt_avg_deviation``: the standard deviation seen on the - number of cycles between interrupts used to feed the pool. - randomize_va_space ================== diff --git a/drivers/char/random.c b/drivers/char/random.c index c27ebf707380..35c440a0d83c 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -240,8 +240,6 @@ #define CREATE_TRACE_POINTS #include -/* #define ADD_INTERRUPT_BENCH */ - enum { POOL_BITS = BLAKE2S_HASH_SIZE * 8, POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ @@ -808,27 +806,6 @@ EXPORT_SYMBOL_GPL(add_input_randomness); static DEFINE_PER_CPU(struct fast_pool, irq_randomness); -#ifdef ADD_INTERRUPT_BENCH -static unsigned long avg_cycles, avg_deviation; - -#define AVG_SHIFT 8 /* Exponential average factor k=1/256 */ -#define FIXED_1_2 (1 << (AVG_SHIFT - 1)) - -static void add_interrupt_bench(cycles_t start) -{ - long delta = random_get_entropy() - start; - - /* Use a weighted moving average */ - delta = delta - ((avg_cycles + FIXED_1_2) >> AVG_SHIFT); - avg_cycles += delta; - /* And average deviation */ - delta = abs(delta) - ((avg_deviation + FIXED_1_2) >> AVG_SHIFT); - avg_deviation += delta; -} -#else -#define add_interrupt_bench(x) -#endif - static u32 get_reg(struct fast_pool *f, struct pt_regs *regs) { u32 *ptr = (u32 *)regs; @@ -865,7 +842,6 @@ void add_interrupt_randomness(int irq) (sizeof(ip) > 4) ? ip >> 32 : get_reg(fast_pool, regs); fast_mix(fast_pool); - add_interrupt_bench(cycles); if (unlikely(crng_init == 0)) { if (fast_pool->count >= 64 && @@ -1574,22 +1550,6 @@ static struct ctl_table random_table[] = { .mode = 0444, .proc_handler = proc_do_uuid, }, -#ifdef ADD_INTERRUPT_BENCH - { - .procname = "add_interrupt_avg_cycles", - .data = &avg_cycles, - .maxlen = sizeof(avg_cycles), - .mode = 0444, - .proc_handler = proc_doulongvec_minmax, - }, - { - .procname = "add_interrupt_avg_deviation", - .data = &avg_deviation, - .maxlen = sizeof(avg_deviation), - .mode = 0444, - .proc_handler = proc_doulongvec_minmax, - }, -#endif { } }; -- cgit v1.2.3 From 14c174633f349cb41ea90c2c0aaddac157012f74 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 10 Feb 2022 16:40:44 +0100 Subject: random: remove unused tracepoints These explicit tracepoints aren't really used and show sign of aging. It's work to keep these up to date, and before I attempted to keep them up to date, they weren't up to date, which indicates that they're not really used. These days there are better ways of introspecting anyway. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 30 +----- include/trace/events/random.h | 212 ------------------------------------------ lib/random32.c | 2 - 3 files changed, 3 insertions(+), 241 deletions(-) delete mode 100644 include/trace/events/random.h diff --git a/drivers/char/random.c b/drivers/char/random.c index 35c440a0d83c..055c42246b68 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -237,9 +237,6 @@ #include #include -#define CREATE_TRACE_POINTS -#include - enum { POOL_BITS = BLAKE2S_HASH_SIZE * 8, POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ @@ -315,7 +312,6 @@ static void mix_pool_bytes(const void *in, size_t nbytes) { unsigned long flags; - trace_mix_pool_bytes(nbytes, _RET_IP_); spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(in, nbytes); spin_unlock_irqrestore(&input_pool.lock, flags); @@ -389,8 +385,6 @@ static void credit_entropy_bits(size_t nbits) entropy_count = min_t(unsigned int, POOL_BITS, orig + add); } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); - trace_credit_entropy_bits(nbits, entropy_count, _RET_IP_); - if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) crng_reseed(); } @@ -721,7 +715,6 @@ void add_device_randomness(const void *buf, size_t size) if (!crng_ready() && size) crng_slow_load(buf, size); - trace_add_device_randomness(size, _RET_IP_); spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(buf, size); _mix_pool_bytes(&time, sizeof(time)); @@ -800,7 +793,6 @@ void add_input_randomness(unsigned int type, unsigned int code, last_value = value; add_timer_randomness(&input_timer_state, (type << 4) ^ code ^ (code >> 4) ^ value); - trace_add_input_randomness(input_pool.entropy_count); } EXPORT_SYMBOL_GPL(add_input_randomness); @@ -880,7 +872,6 @@ void add_disk_randomness(struct gendisk *disk) return; /* first major is 1, so we get >= 0x200 here */ add_timer_randomness(disk->random, 0x100 + disk_devt(disk)); - trace_add_disk_randomness(disk_devt(disk), input_pool.entropy_count); } EXPORT_SYMBOL_GPL(add_disk_randomness); #endif @@ -905,8 +896,6 @@ static void extract_entropy(void *buf, size_t nbytes) } block; size_t i; - trace_extract_entropy(nbytes, input_pool.entropy_count); - for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) { if (!arch_get_random_seed_long(&block.rdseed[i]) && !arch_get_random_long(&block.rdseed[i])) @@ -978,8 +967,6 @@ static void _get_random_bytes(void *buf, size_t nbytes) u8 tmp[CHACHA_BLOCK_SIZE]; size_t len; - trace_get_random_bytes(nbytes, _RET_IP_); - if (!nbytes) return; @@ -1176,7 +1163,6 @@ size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes) size_t left = nbytes; u8 *p = buf; - trace_get_random_bytes_arch(left, _RET_IP_); while (left) { unsigned long v; size_t chunk = min_t(size_t, left, sizeof(unsigned long)); @@ -1260,16 +1246,6 @@ void rand_initialize_disk(struct gendisk *disk) } #endif -static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, - size_t nbytes, loff_t *ppos) -{ - ssize_t ret; - - ret = get_random_bytes_user(buf, nbytes); - trace_urandom_read(nbytes, input_pool.entropy_count); - return ret; -} - static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { @@ -1282,7 +1258,7 @@ static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, current->comm, nbytes); } - return urandom_read_nowarn(file, buf, nbytes, ppos); + return get_random_bytes_user(buf, nbytes); } static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, @@ -1293,7 +1269,7 @@ static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, ret = wait_for_random_bytes(); if (ret != 0) return ret; - return urandom_read_nowarn(file, buf, nbytes, ppos); + return get_random_bytes_user(buf, nbytes); } static __poll_t random_poll(struct file *file, poll_table *wait) @@ -1454,7 +1430,7 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, if (unlikely(ret)) return ret; } - return urandom_read_nowarn(NULL, buf, count, NULL); + return get_random_bytes_user(buf, count); } /******************************************************************** diff --git a/include/trace/events/random.h b/include/trace/events/random.h deleted file mode 100644 index 0609a2810a12..000000000000 --- a/include/trace/events/random.h +++ /dev/null @@ -1,212 +0,0 @@ -/* SPDX-License-Identifier: GPL-2.0 */ -#undef TRACE_SYSTEM -#define TRACE_SYSTEM random - -#if !defined(_TRACE_RANDOM_H) || defined(TRACE_HEADER_MULTI_READ) -#define _TRACE_RANDOM_H - -#include -#include - -TRACE_EVENT(add_device_randomness, - TP_PROTO(size_t bytes, unsigned long IP), - - TP_ARGS(bytes, IP), - - TP_STRUCT__entry( - __field(size_t, bytes ) - __field(unsigned long, IP ) - ), - - TP_fast_assign( - __entry->bytes = bytes; - __entry->IP = IP; - ), - - TP_printk("bytes %zu caller %pS", - __entry->bytes, (void *)__entry->IP) -); - -DECLARE_EVENT_CLASS(random__mix_pool_bytes, - TP_PROTO(size_t bytes, unsigned long IP), - - TP_ARGS(bytes, IP), - - TP_STRUCT__entry( - __field(size_t, bytes ) - __field(unsigned long, IP ) - ), - - TP_fast_assign( - __entry->bytes = bytes; - __entry->IP = IP; - ), - - TP_printk("input pool: bytes %zu caller %pS", - __entry->bytes, (void *)__entry->IP) -); - -DEFINE_EVENT(random__mix_pool_bytes, mix_pool_bytes, - TP_PROTO(size_t bytes, unsigned long IP), - - TP_ARGS(bytes, IP) -); - -DEFINE_EVENT(random__mix_pool_bytes, mix_pool_bytes_nolock, - TP_PROTO(int bytes, unsigned long IP), - - TP_ARGS(bytes, IP) -); - -TRACE_EVENT(credit_entropy_bits, - TP_PROTO(size_t bits, size_t entropy_count, unsigned long IP), - - TP_ARGS(bits, entropy_count, IP), - - TP_STRUCT__entry( - __field(size_t, bits ) - __field(size_t, entropy_count ) - __field(unsigned long, IP ) - ), - - TP_fast_assign( - __entry->bits = bits; - __entry->entropy_count = entropy_count; - __entry->IP = IP; - ), - - TP_printk("input pool: bits %zu entropy_count %zu caller %pS", - __entry->bits, __entry->entropy_count, (void *)__entry->IP) -); - -TRACE_EVENT(add_input_randomness, - TP_PROTO(size_t input_bits), - - TP_ARGS(input_bits), - - TP_STRUCT__entry( - __field(size_t, input_bits ) - ), - - TP_fast_assign( - __entry->input_bits = input_bits; - ), - - TP_printk("input_pool_bits %zu", __entry->input_bits) -); - -TRACE_EVENT(add_disk_randomness, - TP_PROTO(dev_t dev, size_t input_bits), - - TP_ARGS(dev, input_bits), - - TP_STRUCT__entry( - __field(dev_t, dev ) - __field(size_t, input_bits ) - ), - - TP_fast_assign( - __entry->dev = dev; - __entry->input_bits = input_bits; - ), - - TP_printk("dev %d,%d input_pool_bits %zu", MAJOR(__entry->dev), - MINOR(__entry->dev), __entry->input_bits) -); - -DECLARE_EVENT_CLASS(random__get_random_bytes, - TP_PROTO(size_t nbytes, unsigned long IP), - - TP_ARGS(nbytes, IP), - - TP_STRUCT__entry( - __field(size_t, nbytes ) - __field(unsigned long, IP ) - ), - - TP_fast_assign( - __entry->nbytes = nbytes; - __entry->IP = IP; - ), - - TP_printk("nbytes %zu caller %pS", __entry->nbytes, (void *)__entry->IP) -); - -DEFINE_EVENT(random__get_random_bytes, get_random_bytes, - TP_PROTO(size_t nbytes, unsigned long IP), - - TP_ARGS(nbytes, IP) -); - -DEFINE_EVENT(random__get_random_bytes, get_random_bytes_arch, - TP_PROTO(size_t nbytes, unsigned long IP), - - TP_ARGS(nbytes, IP) -); - -DECLARE_EVENT_CLASS(random__extract_entropy, - TP_PROTO(size_t nbytes, size_t entropy_count), - - TP_ARGS(nbytes, entropy_count), - - TP_STRUCT__entry( - __field( size_t, nbytes ) - __field( size_t, entropy_count ) - ), - - TP_fast_assign( - __entry->nbytes = nbytes; - __entry->entropy_count = entropy_count; - ), - - TP_printk("input pool: nbytes %zu entropy_count %zu", - __entry->nbytes, __entry->entropy_count) -); - - -DEFINE_EVENT(random__extract_entropy, extract_entropy, - TP_PROTO(size_t nbytes, size_t entropy_count), - - TP_ARGS(nbytes, entropy_count) -); - -TRACE_EVENT(urandom_read, - TP_PROTO(size_t nbytes, size_t entropy_count), - - TP_ARGS(nbytes, entropy_count), - - TP_STRUCT__entry( - __field( size_t, nbytes ) - __field( size_t, entropy_count ) - ), - - TP_fast_assign( - __entry->nbytes = nbytes; - __entry->entropy_count = entropy_count; - ), - - TP_printk("reading: nbytes %zu entropy_count %zu", - __entry->nbytes, __entry->entropy_count) -); - -TRACE_EVENT(prandom_u32, - - TP_PROTO(unsigned int ret), - - TP_ARGS(ret), - - TP_STRUCT__entry( - __field( unsigned int, ret) - ), - - TP_fast_assign( - __entry->ret = ret; - ), - - TP_printk("ret=%u" , __entry->ret) -); - -#endif /* _TRACE_RANDOM_H */ - -/* This part must be outside protection */ -#include diff --git a/lib/random32.c b/lib/random32.c index a57a0e18819d..3c19820796d0 100644 --- a/lib/random32.c +++ b/lib/random32.c @@ -41,7 +41,6 @@ #include #include #include -#include /** * prandom_u32_state - seeded pseudo-random number generator. @@ -387,7 +386,6 @@ u32 prandom_u32(void) struct siprand_state *state = get_cpu_ptr(&net_rand_state); u32 res = siprand_u32(state); - trace_prandom_u32(res); put_cpu_ptr(&net_rand_state); return res; } -- cgit v1.2.3 From a07fdae346c35c6ba286af1c88e0effcfa330bf9 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 10 Feb 2022 16:43:57 +0100 Subject: random: add proper SPDX header Convert the current license into the SPDX notation of "(GPL-2.0 OR BSD-3-Clause)". This infers GPL-2.0 from the text "ALTERNATIVELY, this product may be distributed under the terms of the GNU General Public License, in which case the provisions of the GPL are required INSTEAD OF the above restrictions" and it infers BSD-3-Clause from the verbatim BSD 3 clause license in the file. Cc: Thomas Gleixner Cc: Theodore Ts'o Cc: Dominik Brodowski Reviewed-by: Greg Kroah-Hartman Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 37 +------------------------------------ 1 file changed, 1 insertion(+), 36 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 055c42246b68..5373fae0aa63 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1,44 +1,9 @@ +// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) /* - * random.c -- A strong random number generator - * * Copyright (C) 2017-2022 Jason A. Donenfeld . All Rights Reserved. - * * Copyright Matt Mackall , 2003, 2004, 2005 - * * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All * rights reserved. - * - * Redistribution and use in source and binary forms, with or without - * modification, are permitted provided that the following conditions - * are met: - * 1. Redistributions of source code must retain the above copyright - * notice, and the entire permission notice in its entirety, - * including the disclaimer of warranties. - * 2. Redistributions in binary form must reproduce the above copyright - * notice, this list of conditions and the following disclaimer in the - * documentation and/or other materials provided with the distribution. - * 3. The name of the author may not be used to endorse or promote - * products derived from this software without specific prior - * written permission. - * - * ALTERNATIVELY, this product may be distributed under the terms of - * the GNU General Public License, in which case the provisions of the GPL are - * required INSTEAD OF the above restrictions. (This clause is - * necessary due to a potential bad interaction between the GPL and - * the restrictions contained in a BSD-style copyright.) - * - * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED - * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES - * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF - * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE - * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR - * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT - * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR - * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF - * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT - * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE - * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH - * DAMAGE. */ /* -- cgit v1.2.3 From b2f408fe403800c91a49f6589d95b6759ce1b30b Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 10 Feb 2022 17:01:27 +0100 Subject: random: deobfuscate irq u32/u64 contributions In the irq handler, we fill out 16 bytes differently on 32-bit and 64-bit platforms, and for 32-bit vs 64-bit cycle counters, which doesn't always correspond with the bitness of the platform. Whether or not you like this strangeness, it is a matter of fact. But it might not be a fact you well realized until now, because the code that loaded the irq info into 4 32-bit words was quite confusing. Instead, this commit makes everything explicit by having separate (compile-time) branches for 32-bit and 64-bit types. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 49 ++++++++++++++++++++++++++++--------------------- 1 file changed, 28 insertions(+), 21 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 5373fae0aa63..e7571de3d91a 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -283,7 +283,10 @@ static void mix_pool_bytes(const void *in, size_t nbytes) } struct fast_pool { - u32 pool[4]; + union { + u32 pool32[4]; + u64 pool64[2]; + }; unsigned long last; u16 reg_idx; u8 count; @@ -294,10 +297,10 @@ struct fast_pool { * collector. It's hardcoded for an 128 bit pool and assumes that any * locks that might be needed are taken by the caller. */ -static void fast_mix(struct fast_pool *f) +static void fast_mix(u32 pool[4]) { - u32 a = f->pool[0], b = f->pool[1]; - u32 c = f->pool[2], d = f->pool[3]; + u32 a = pool[0], b = pool[1]; + u32 c = pool[2], d = pool[3]; a += b; c += d; b = rol32(b, 6); d = rol32(d, 27); @@ -315,9 +318,8 @@ static void fast_mix(struct fast_pool *f) b = rol32(b, 16); d = rol32(d, 14); d ^= a; b ^= c; - f->pool[0] = a; f->pool[1] = b; - f->pool[2] = c; f->pool[3] = d; - f->count++; + pool[0] = a; pool[1] = b; + pool[2] = c; pool[3] = d; } static void process_random_ready_list(void) @@ -784,29 +786,34 @@ void add_interrupt_randomness(int irq) struct pt_regs *regs = get_irq_regs(); unsigned long now = jiffies; cycles_t cycles = random_get_entropy(); - u32 c_high, j_high; - u64 ip; if (cycles == 0) cycles = get_reg(fast_pool, regs); - c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0; - j_high = (sizeof(now) > 4) ? now >> 32 : 0; - fast_pool->pool[0] ^= cycles ^ j_high ^ irq; - fast_pool->pool[1] ^= now ^ c_high; - ip = regs ? instruction_pointer(regs) : _RET_IP_; - fast_pool->pool[2] ^= ip; - fast_pool->pool[3] ^= - (sizeof(ip) > 4) ? ip >> 32 : get_reg(fast_pool, regs); - fast_mix(fast_pool); + if (sizeof(cycles) == 8) + fast_pool->pool64[0] ^= cycles ^ rol64(now, 32) ^ irq; + else { + fast_pool->pool32[0] ^= cycles ^ irq; + fast_pool->pool32[1] ^= now; + } + + if (sizeof(unsigned long) == 8) + fast_pool->pool64[1] ^= regs ? instruction_pointer(regs) : _RET_IP_; + else { + fast_pool->pool32[2] ^= regs ? instruction_pointer(regs) : _RET_IP_; + fast_pool->pool32[3] ^= get_reg(fast_pool, regs); + } + + fast_mix(fast_pool->pool32); + ++fast_pool->count; if (unlikely(crng_init == 0)) { if (fast_pool->count >= 64 && - crng_fast_load(fast_pool->pool, sizeof(fast_pool->pool)) > 0) { + crng_fast_load(fast_pool->pool32, sizeof(fast_pool->pool32)) > 0) { fast_pool->count = 0; fast_pool->last = now; if (spin_trylock(&input_pool.lock)) { - _mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool)); + _mix_pool_bytes(&fast_pool->pool32, sizeof(fast_pool->pool32)); spin_unlock(&input_pool.lock); } } @@ -820,7 +827,7 @@ void add_interrupt_randomness(int irq) return; fast_pool->last = now; - _mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool)); + _mix_pool_bytes(&fast_pool->pool32, sizeof(fast_pool->pool32)); spin_unlock(&input_pool.lock); fast_pool->count = 0; -- cgit v1.2.3 From 246c03dd899164d0186b6d685d6387f228c28d93 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:19:49 +0100 Subject: random: introduce drain_entropy() helper to declutter crng_reseed() In preparation for separating responsibilities, break out the entropy count management part of crng_reseed() into its own function. No functional changes. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index e7571de3d91a..d9a31ac10daf 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -260,6 +260,7 @@ static struct { }; static void extract_entropy(void *buf, size_t nbytes); +static bool drain_entropy(void *buf, size_t nbytes); static void crng_reseed(void); @@ -456,23 +457,13 @@ static void crng_slow_load(const void *cp, size_t len) static void crng_reseed(void) { unsigned long flags; - int entropy_count; unsigned long next_gen; u8 key[CHACHA_KEY_SIZE]; bool finalize_init = false; - /* - * First we make sure we have POOL_MIN_BITS of entropy in the pool, - * and then we drain all of it. Only then can we extract a new key. - */ - do { - entropy_count = READ_ONCE(input_pool.entropy_count); - if (entropy_count < POOL_MIN_BITS) - return; - } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); - extract_entropy(key, sizeof(key)); - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); + /* Only reseed if we can, to prevent brute forcing a small amount of new bits. */ + if (!drain_entropy(key, sizeof(key))) + return; /* * We copy the new key into the base_crng, overwriting the old one, @@ -900,6 +891,25 @@ static void extract_entropy(void *buf, size_t nbytes) memzero_explicit(&block, sizeof(block)); } +/* + * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we + * set the entropy count to zero (but don't actually touch any data). Only then + * can we extract a new key with extract_entropy(). + */ +static bool drain_entropy(void *buf, size_t nbytes) +{ + unsigned int entropy_count; + do { + entropy_count = READ_ONCE(input_pool.entropy_count); + if (entropy_count < POOL_MIN_BITS) + return false; + } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); + extract_entropy(buf, nbytes); + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + return true; +} + #define warn_unseeded_randomness(previous) \ _warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous)) -- cgit v1.2.3 From 6071a6c0fba2d747742cadcbb3ba26ed756ed73b Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:28:33 +0100 Subject: random: remove useless header comment This really adds nothing at all useful. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- include/linux/random.h | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/include/linux/random.h b/include/linux/random.h index e92efb39779c..37e1e8c43d7e 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -1,9 +1,5 @@ /* SPDX-License-Identifier: GPL-2.0 */ -/* - * include/linux/random.h - * - * Include file for the random number generator. - */ + #ifndef _LINUX_RANDOM_H #define _LINUX_RANDOM_H -- cgit v1.2.3 From 87e7d5abad0cbc9312dea7f889a57d294c1a5fcc Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 13:41:41 +0100 Subject: random: remove whitespace and reorder includes This is purely cosmetic. Future work involves figuring out which of these headers we need and which we don't. Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index d9a31ac10daf..ad112f928182 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -193,11 +193,10 @@ #include #include #include +#include #include #include - #include -#include #include #include #include -- cgit v1.2.3 From 5f1bb112006b104b3e2a1e1b39bbb9b2617581e6 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:53:34 +0100 Subject: random: group initialization wait functions This pulls all of the readiness waiting-focused functions into the first labeled section. No functional changes. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 333 ++++++++++++++++++++++++++------------------------ 1 file changed, 172 insertions(+), 161 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index ad112f928182..dd2da0b12350 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -201,44 +201,197 @@ #include #include -enum { - POOL_BITS = BLAKE2S_HASH_SIZE * 8, - POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ -}; - -/* - * Static global variables - */ -static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); -static struct fasync_struct *fasync; - -static DEFINE_SPINLOCK(random_ready_list_lock); -static LIST_HEAD(random_ready_list); +/********************************************************************* + * + * Initialization and readiness waiting. + * + * Much of the RNG infrastructure is devoted to various dependencies + * being able to wait until the RNG has collected enough entropy and + * is ready for safe consumption. + * + *********************************************************************/ /* * crng_init = 0 --> Uninitialized * 1 --> Initialized * 2 --> Initialized from input_pool * - * crng_init is protected by primary_crng->lock, and only increases + * crng_init is protected by base_crng->lock, and only increases * its value (from 0->1->2). */ static int crng_init = 0; #define crng_ready() (likely(crng_init > 1)) -static int crng_init_cnt = 0; -static void process_random_ready_list(void); -static void _get_random_bytes(void *buf, size_t nbytes); +/* Various types of waiters for crng_init->2 transition. */ +static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); +static struct fasync_struct *fasync; +static DEFINE_SPINLOCK(random_ready_list_lock); +static LIST_HEAD(random_ready_list); +/* Control how we warn userspace. */ static struct ratelimit_state unseeded_warning = RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3); static struct ratelimit_state urandom_warning = RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3); - static int ratelimit_disable __read_mostly; - module_param_named(ratelimit_disable, ratelimit_disable, int, 0644); MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression"); +/* + * Returns whether or not the input pool has been seeded and thus guaranteed + * to supply cryptographically secure random numbers. This applies to: the + * /dev/urandom device, the get_random_bytes function, and the get_random_{u32, + * ,u64,int,long} family of functions. + * + * Returns: true if the input pool has been seeded. + * false if the input pool has not been seeded. + */ +bool rng_is_initialized(void) +{ + return crng_ready(); +} +EXPORT_SYMBOL(rng_is_initialized); + +/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */ +static void try_to_generate_entropy(void); + +/* + * Wait for the input pool to be seeded and thus guaranteed to supply + * cryptographically secure random numbers. This applies to: the /dev/urandom + * device, the get_random_bytes function, and the get_random_{u32,u64,int,long} + * family of functions. Using any of these functions without first calling + * this function forfeits the guarantee of security. + * + * Returns: 0 if the input pool has been seeded. + * -ERESTARTSYS if the function was interrupted by a signal. + */ +int wait_for_random_bytes(void) +{ + if (likely(crng_ready())) + return 0; + + do { + int ret; + ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ); + if (ret) + return ret > 0 ? 0 : ret; + + try_to_generate_entropy(); + } while (!crng_ready()); + + return 0; +} +EXPORT_SYMBOL(wait_for_random_bytes); + +/* + * Add a callback function that will be invoked when the input + * pool is initialised. + * + * returns: 0 if callback is successfully added + * -EALREADY if pool is already initialised (callback not called) + * -ENOENT if module for callback is not alive + */ +int add_random_ready_callback(struct random_ready_callback *rdy) +{ + struct module *owner; + unsigned long flags; + int err = -EALREADY; + + if (crng_ready()) + return err; + + owner = rdy->owner; + if (!try_module_get(owner)) + return -ENOENT; + + spin_lock_irqsave(&random_ready_list_lock, flags); + if (crng_ready()) + goto out; + + owner = NULL; + + list_add(&rdy->list, &random_ready_list); + err = 0; + +out: + spin_unlock_irqrestore(&random_ready_list_lock, flags); + + module_put(owner); + + return err; +} +EXPORT_SYMBOL(add_random_ready_callback); + +/* + * Delete a previously registered readiness callback function. + */ +void del_random_ready_callback(struct random_ready_callback *rdy) +{ + unsigned long flags; + struct module *owner = NULL; + + spin_lock_irqsave(&random_ready_list_lock, flags); + if (!list_empty(&rdy->list)) { + list_del_init(&rdy->list); + owner = rdy->owner; + } + spin_unlock_irqrestore(&random_ready_list_lock, flags); + + module_put(owner); +} +EXPORT_SYMBOL(del_random_ready_callback); + +static void process_random_ready_list(void) +{ + unsigned long flags; + struct random_ready_callback *rdy, *tmp; + + spin_lock_irqsave(&random_ready_list_lock, flags); + list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) { + struct module *owner = rdy->owner; + + list_del_init(&rdy->list); + rdy->func(rdy); + module_put(owner); + } + spin_unlock_irqrestore(&random_ready_list_lock, flags); +} + +#define warn_unseeded_randomness(previous) \ + _warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous)) + +static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous) +{ +#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM + const bool print_once = false; +#else + static bool print_once __read_mostly; +#endif + + if (print_once || crng_ready() || + (previous && (caller == READ_ONCE(*previous)))) + return; + WRITE_ONCE(*previous, caller); +#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM + print_once = true; +#endif + if (__ratelimit(&unseeded_warning)) + printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", + func_name, caller, crng_init); +} + + +enum { + POOL_BITS = BLAKE2S_HASH_SIZE * 8, + POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ +}; + +/* + * Static global variables + */ +static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); + +static int crng_init_cnt = 0; + /********************************************************************** * * OS independent entropy store. Here are the functions which handle @@ -322,22 +475,6 @@ static void fast_mix(u32 pool[4]) pool[2] = c; pool[3] = d; } -static void process_random_ready_list(void) -{ - unsigned long flags; - struct random_ready_callback *rdy, *tmp; - - spin_lock_irqsave(&random_ready_list_lock, flags); - list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) { - struct module *owner = rdy->owner; - - list_del_init(&rdy->list); - rdy->func(rdy); - module_put(owner); - } - spin_unlock_irqrestore(&random_ready_list_lock, flags); -} - static void credit_entropy_bits(size_t nbits) { unsigned int entropy_count, orig, add; @@ -387,8 +524,6 @@ static DEFINE_PER_CPU(struct crng, crngs) = { .lock = INIT_LOCAL_LOCK(crngs.lock), }; -static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); - /* * crng_fast_load() can be called by code in the interrupt service * path. So we can't afford to dilly-dally. Returns the number of @@ -909,29 +1044,6 @@ static bool drain_entropy(void *buf, size_t nbytes) return true; } -#define warn_unseeded_randomness(previous) \ - _warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous)) - -static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous) -{ -#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM - const bool print_once = false; -#else - static bool print_once __read_mostly; -#endif - - if (print_once || crng_ready() || - (previous && (caller == READ_ONCE(*previous)))) - return; - WRITE_ONCE(*previous, caller); -#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM - print_once = true; -#endif - if (__ratelimit(&unseeded_warning)) - printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", - func_name, caller, crng_init); -} - /* * This function is the exported kernel interface. It returns some * number of good random numbers, suitable for key generation, seeding @@ -1032,107 +1144,6 @@ static void try_to_generate_entropy(void) mix_pool_bytes(&stack.now, sizeof(stack.now)); } -/* - * Wait for the urandom pool to be seeded and thus guaranteed to supply - * cryptographically secure random numbers. This applies to: the /dev/urandom - * device, the get_random_bytes function, and the get_random_{u32,u64,int,long} - * family of functions. Using any of these functions without first calling - * this function forfeits the guarantee of security. - * - * Returns: 0 if the urandom pool has been seeded. - * -ERESTARTSYS if the function was interrupted by a signal. - */ -int wait_for_random_bytes(void) -{ - if (likely(crng_ready())) - return 0; - - do { - int ret; - ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ); - if (ret) - return ret > 0 ? 0 : ret; - - try_to_generate_entropy(); - } while (!crng_ready()); - - return 0; -} -EXPORT_SYMBOL(wait_for_random_bytes); - -/* - * Returns whether or not the urandom pool has been seeded and thus guaranteed - * to supply cryptographically secure random numbers. This applies to: the - * /dev/urandom device, the get_random_bytes function, and the get_random_{u32, - * ,u64,int,long} family of functions. - * - * Returns: true if the urandom pool has been seeded. - * false if the urandom pool has not been seeded. - */ -bool rng_is_initialized(void) -{ - return crng_ready(); -} -EXPORT_SYMBOL(rng_is_initialized); - -/* - * Add a callback function that will be invoked when the nonblocking - * pool is initialised. - * - * returns: 0 if callback is successfully added - * -EALREADY if pool is already initialised (callback not called) - * -ENOENT if module for callback is not alive - */ -int add_random_ready_callback(struct random_ready_callback *rdy) -{ - struct module *owner; - unsigned long flags; - int err = -EALREADY; - - if (crng_ready()) - return err; - - owner = rdy->owner; - if (!try_module_get(owner)) - return -ENOENT; - - spin_lock_irqsave(&random_ready_list_lock, flags); - if (crng_ready()) - goto out; - - owner = NULL; - - list_add(&rdy->list, &random_ready_list); - err = 0; - -out: - spin_unlock_irqrestore(&random_ready_list_lock, flags); - - module_put(owner); - - return err; -} -EXPORT_SYMBOL(add_random_ready_callback); - -/* - * Delete a previously registered readiness callback function. - */ -void del_random_ready_callback(struct random_ready_callback *rdy) -{ - unsigned long flags; - struct module *owner = NULL; - - spin_lock_irqsave(&random_ready_list_lock, flags); - if (!list_empty(&rdy->list)) { - list_del_init(&rdy->list); - owner = rdy->owner; - } - spin_unlock_irqrestore(&random_ready_list_lock, flags); - - module_put(owner); -} -EXPORT_SYMBOL(del_random_ready_callback); - /* * This function will use the architecture-specific hardware random * number generator if it is available. It is not recommended for -- cgit v1.2.3 From 3655adc7089da4f8ca74cec8fcef73ea5101430e Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:53:34 +0100 Subject: random: group crng functions This pulls all of the crng-focused functions into the second labeled section. No functional changes. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 862 ++++++++++++++++++++++++++------------------------ 1 file changed, 445 insertions(+), 417 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index dd2da0b12350..99b55e76b004 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -380,122 +380,27 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller, void } -enum { - POOL_BITS = BLAKE2S_HASH_SIZE * 8, - POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ -}; - -/* - * Static global variables - */ -static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); - -static int crng_init_cnt = 0; - -/********************************************************************** +/********************************************************************* * - * OS independent entropy store. Here are the functions which handle - * storing entropy in an entropy pool. + * Fast key erasure RNG, the "crng". * - **********************************************************************/ - -static struct { - struct blake2s_state hash; - spinlock_t lock; - unsigned int entropy_count; -} input_pool = { - .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE), - BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4, - BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 }, - .hash.outlen = BLAKE2S_HASH_SIZE, - .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), -}; - -static void extract_entropy(void *buf, size_t nbytes); -static bool drain_entropy(void *buf, size_t nbytes); - -static void crng_reseed(void); - -/* - * This function adds bytes into the entropy "pool". It does not - * update the entropy estimate. The caller should call - * credit_entropy_bits if this is appropriate. - */ -static void _mix_pool_bytes(const void *in, size_t nbytes) -{ - blake2s_update(&input_pool.hash, in, nbytes); -} - -static void mix_pool_bytes(const void *in, size_t nbytes) -{ - unsigned long flags; - - spin_lock_irqsave(&input_pool.lock, flags); - _mix_pool_bytes(in, nbytes); - spin_unlock_irqrestore(&input_pool.lock, flags); -} - -struct fast_pool { - union { - u32 pool32[4]; - u64 pool64[2]; - }; - unsigned long last; - u16 reg_idx; - u8 count; -}; - -/* - * This is a fast mixing routine used by the interrupt randomness - * collector. It's hardcoded for an 128 bit pool and assumes that any - * locks that might be needed are taken by the caller. - */ -static void fast_mix(u32 pool[4]) -{ - u32 a = pool[0], b = pool[1]; - u32 c = pool[2], d = pool[3]; - - a += b; c += d; - b = rol32(b, 6); d = rol32(d, 27); - d ^= a; b ^= c; - - a += b; c += d; - b = rol32(b, 16); d = rol32(d, 14); - d ^= a; b ^= c; - - a += b; c += d; - b = rol32(b, 6); d = rol32(d, 27); - d ^= a; b ^= c; - - a += b; c += d; - b = rol32(b, 16); d = rol32(d, 14); - d ^= a; b ^= c; - - pool[0] = a; pool[1] = b; - pool[2] = c; pool[3] = d; -} - -static void credit_entropy_bits(size_t nbits) -{ - unsigned int entropy_count, orig, add; - - if (!nbits) - return; - - add = min_t(size_t, nbits, POOL_BITS); - - do { - orig = READ_ONCE(input_pool.entropy_count); - entropy_count = min_t(unsigned int, POOL_BITS, orig + add); - } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); - - if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) - crng_reseed(); -} - -/********************************************************************* + * These functions expand entropy from the entropy extractor into + * long streams for external consumption using the "fast key erasure" + * RNG described at . * - * CRNG using CHACHA20 + * There are a few exported interfaces for use by other drivers: + * + * void get_random_bytes(void *buf, size_t nbytes) + * u32 get_random_u32() + * u64 get_random_u64() + * unsigned int get_random_int() + * unsigned long get_random_long() + * + * These interfaces will return the requested number of random bytes + * into the given buffer or as a return value. This is equivalent to + * a read from /dev/urandom. The integer family of functions may be + * higher performance for one-off random integers, because they do a + * bit of buffering. * *********************************************************************/ @@ -524,70 +429,14 @@ static DEFINE_PER_CPU(struct crng, crngs) = { .lock = INIT_LOCAL_LOCK(crngs.lock), }; -/* - * crng_fast_load() can be called by code in the interrupt service - * path. So we can't afford to dilly-dally. Returns the number of - * bytes processed from cp. - */ -static size_t crng_fast_load(const void *cp, size_t len) -{ - unsigned long flags; - const u8 *src = (const u8 *)cp; - size_t ret = 0; - - if (!spin_trylock_irqsave(&base_crng.lock, flags)) - return 0; - if (crng_init != 0) { - spin_unlock_irqrestore(&base_crng.lock, flags); - return 0; - } - while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) { - base_crng.key[crng_init_cnt % sizeof(base_crng.key)] ^= *src; - src++; crng_init_cnt++; len--; ret++; - } - if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { - ++base_crng.generation; - crng_init = 1; - } - spin_unlock_irqrestore(&base_crng.lock, flags); - if (crng_init == 1) - pr_notice("fast init done\n"); - return ret; -} +/* Used by crng_reseed() to extract a new seed from the input pool. */ +static bool drain_entropy(void *buf, size_t nbytes); /* - * crng_slow_load() is called by add_device_randomness, which has two - * attributes. (1) We can't trust the buffer passed to it is - * guaranteed to be unpredictable (so it might not have any entropy at - * all), and (2) it doesn't have the performance constraints of - * crng_fast_load(). - * - * So, we simply hash the contents in with the current key. Finally, - * we do *not* advance crng_init_cnt since buffer we may get may be - * something like a fixed DMI table (for example), which might very - * well be unique to the machine, but is otherwise unvarying. + * This extracts a new crng key from the input pool, but only if there is a + * sufficient amount of entropy available, in order to mitigate bruteforcing + * of newly added bits. */ -static void crng_slow_load(const void *cp, size_t len) -{ - unsigned long flags; - struct blake2s_state hash; - - blake2s_init(&hash, sizeof(base_crng.key)); - - if (!spin_trylock_irqsave(&base_crng.lock, flags)) - return; - if (crng_init != 0) { - spin_unlock_irqrestore(&base_crng.lock, flags); - return; - } - - blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); - blake2s_update(&hash, cp, len); - blake2s_final(&hash, base_crng.key); - - spin_unlock_irqrestore(&base_crng.lock, flags); -} - static void crng_reseed(void) { unsigned long flags; @@ -637,13 +486,11 @@ static void crng_reseed(void) } /* - * The general form here is based on a "fast key erasure RNG" from - * . It generates a ChaCha - * block using the provided key, and then immediately overwites that - * key with half the block. It returns the resultant ChaCha state to the - * user, along with the second half of the block containing 32 bytes of - * random data that may be used; random_data_len may not be greater than - * 32. + * This generates a ChaCha block using the provided key, and then + * immediately overwites that key with half the block. It returns + * the resultant ChaCha state to the user, along with the second + * half of the block containing 32 bytes of random data that may + * be used; random_data_len may not be greater than 32. */ static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], u32 chacha_state[CHACHA_STATE_WORDS], @@ -730,51 +577,433 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], local_unlock_irqrestore(&crngs.lock, flags); } -static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) +/* + * This function is for crng_init == 0 only. + * + * crng_fast_load() can be called by code in the interrupt service + * path. So we can't afford to dilly-dally. Returns the number of + * bytes processed from cp. + */ +static size_t crng_fast_load(const void *cp, size_t len) +{ + static int crng_init_cnt = 0; + unsigned long flags; + const u8 *src = (const u8 *)cp; + size_t ret = 0; + + if (!spin_trylock_irqsave(&base_crng.lock, flags)) + return 0; + if (crng_init != 0) { + spin_unlock_irqrestore(&base_crng.lock, flags); + return 0; + } + while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) { + base_crng.key[crng_init_cnt % sizeof(base_crng.key)] ^= *src; + src++; crng_init_cnt++; len--; ret++; + } + if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { + ++base_crng.generation; + crng_init = 1; + } + spin_unlock_irqrestore(&base_crng.lock, flags); + if (crng_init == 1) + pr_notice("fast init done\n"); + return ret; +} + +/* + * This function is for crng_init == 0 only. + * + * crng_slow_load() is called by add_device_randomness, which has two + * attributes. (1) We can't trust the buffer passed to it is + * guaranteed to be unpredictable (so it might not have any entropy at + * all), and (2) it doesn't have the performance constraints of + * crng_fast_load(). + * + * So, we simply hash the contents in with the current key. Finally, + * we do *not* advance crng_init_cnt since buffer we may get may be + * something like a fixed DMI table (for example), which might very + * well be unique to the machine, but is otherwise unvarying. + */ +static void crng_slow_load(const void *cp, size_t len) +{ + unsigned long flags; + struct blake2s_state hash; + + blake2s_init(&hash, sizeof(base_crng.key)); + + if (!spin_trylock_irqsave(&base_crng.lock, flags)) + return; + if (crng_init != 0) { + spin_unlock_irqrestore(&base_crng.lock, flags); + return; + } + + blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); + blake2s_update(&hash, cp, len); + blake2s_final(&hash, base_crng.key); + + spin_unlock_irqrestore(&base_crng.lock, flags); +} + +static void _get_random_bytes(void *buf, size_t nbytes) { - bool large_request = nbytes > 256; - ssize_t ret = 0; - size_t len; u32 chacha_state[CHACHA_STATE_WORDS]; - u8 output[CHACHA_BLOCK_SIZE]; + u8 tmp[CHACHA_BLOCK_SIZE]; + size_t len; + + if (!nbytes) + return; + + len = min_t(size_t, 32, nbytes); + crng_make_state(chacha_state, buf, len); + nbytes -= len; + buf += len; + + while (nbytes) { + if (nbytes < CHACHA_BLOCK_SIZE) { + chacha20_block(chacha_state, tmp); + memcpy(buf, tmp, nbytes); + memzero_explicit(tmp, sizeof(tmp)); + break; + } + + chacha20_block(chacha_state, buf); + if (unlikely(chacha_state[12] == 0)) + ++chacha_state[13]; + nbytes -= CHACHA_BLOCK_SIZE; + buf += CHACHA_BLOCK_SIZE; + } + + memzero_explicit(chacha_state, sizeof(chacha_state)); +} + +/* + * This function is the exported kernel interface. It returns some + * number of good random numbers, suitable for key generation, seeding + * TCP sequence numbers, etc. It does not rely on the hardware random + * number generator. For random bytes direct from the hardware RNG + * (when available), use get_random_bytes_arch(). In order to ensure + * that the randomness provided by this function is okay, the function + * wait_for_random_bytes() should be called and return 0 at least once + * at any point prior. + */ +void get_random_bytes(void *buf, size_t nbytes) +{ + static void *previous; + + warn_unseeded_randomness(&previous); + _get_random_bytes(buf, nbytes); +} +EXPORT_SYMBOL(get_random_bytes); + +static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) +{ + bool large_request = nbytes > 256; + ssize_t ret = 0; + size_t len; + u32 chacha_state[CHACHA_STATE_WORDS]; + u8 output[CHACHA_BLOCK_SIZE]; + + if (!nbytes) + return 0; + + len = min_t(size_t, 32, nbytes); + crng_make_state(chacha_state, output, len); + + if (copy_to_user(buf, output, len)) + return -EFAULT; + nbytes -= len; + buf += len; + ret += len; + + while (nbytes) { + if (large_request && need_resched()) { + if (signal_pending(current)) + break; + schedule(); + } + + chacha20_block(chacha_state, output); + if (unlikely(chacha_state[12] == 0)) + ++chacha_state[13]; + + len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE); + if (copy_to_user(buf, output, len)) { + ret = -EFAULT; + break; + } + + nbytes -= len; + buf += len; + ret += len; + } + + memzero_explicit(chacha_state, sizeof(chacha_state)); + memzero_explicit(output, sizeof(output)); + return ret; +} + +/* + * Batched entropy returns random integers. The quality of the random + * number is good as /dev/urandom. In order to ensure that the randomness + * provided by this function is okay, the function wait_for_random_bytes() + * should be called and return 0 at least once at any point prior. + */ +struct batched_entropy { + union { + /* + * We make this 1.5x a ChaCha block, so that we get the + * remaining 32 bytes from fast key erasure, plus one full + * block from the detached ChaCha state. We can increase + * the size of this later if needed so long as we keep the + * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. + */ + u64 entropy_u64[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u64))]; + u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))]; + }; + local_lock_t lock; + unsigned long generation; + unsigned int position; +}; + + +static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = { + .lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock), + .position = UINT_MAX +}; + +u64 get_random_u64(void) +{ + u64 ret; + unsigned long flags; + struct batched_entropy *batch; + static void *previous; + unsigned long next_gen; + + warn_unseeded_randomness(&previous); + + local_lock_irqsave(&batched_entropy_u64.lock, flags); + batch = raw_cpu_ptr(&batched_entropy_u64); + + next_gen = READ_ONCE(base_crng.generation); + if (batch->position >= ARRAY_SIZE(batch->entropy_u64) || + next_gen != batch->generation) { + _get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64)); + batch->position = 0; + batch->generation = next_gen; + } + + ret = batch->entropy_u64[batch->position]; + batch->entropy_u64[batch->position] = 0; + ++batch->position; + local_unlock_irqrestore(&batched_entropy_u64.lock, flags); + return ret; +} +EXPORT_SYMBOL(get_random_u64); + +static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = { + .lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock), + .position = UINT_MAX +}; + +u32 get_random_u32(void) +{ + u32 ret; + unsigned long flags; + struct batched_entropy *batch; + static void *previous; + unsigned long next_gen; + + warn_unseeded_randomness(&previous); + + local_lock_irqsave(&batched_entropy_u32.lock, flags); + batch = raw_cpu_ptr(&batched_entropy_u32); + + next_gen = READ_ONCE(base_crng.generation); + if (batch->position >= ARRAY_SIZE(batch->entropy_u32) || + next_gen != batch->generation) { + _get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32)); + batch->position = 0; + batch->generation = next_gen; + } + + ret = batch->entropy_u32[batch->position]; + batch->entropy_u32[batch->position] = 0; + ++batch->position; + local_unlock_irqrestore(&batched_entropy_u32.lock, flags); + return ret; +} +EXPORT_SYMBOL(get_random_u32); + +/** + * randomize_page - Generate a random, page aligned address + * @start: The smallest acceptable address the caller will take. + * @range: The size of the area, starting at @start, within which the + * random address must fall. + * + * If @start + @range would overflow, @range is capped. + * + * NOTE: Historical use of randomize_range, which this replaces, presumed that + * @start was already page aligned. We now align it regardless. + * + * Return: A page aligned address within [start, start + range). On error, + * @start is returned. + */ +unsigned long randomize_page(unsigned long start, unsigned long range) +{ + if (!PAGE_ALIGNED(start)) { + range -= PAGE_ALIGN(start) - start; + start = PAGE_ALIGN(start); + } + + if (start > ULONG_MAX - range) + range = ULONG_MAX - start; + + range >>= PAGE_SHIFT; + + if (range == 0) + return start; + + return start + (get_random_long() % range << PAGE_SHIFT); +} + +/* + * This function will use the architecture-specific hardware random + * number generator if it is available. It is not recommended for + * use. Use get_random_bytes() instead. It returns the number of + * bytes filled in. + */ +size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes) +{ + size_t left = nbytes; + u8 *p = buf; + + while (left) { + unsigned long v; + size_t chunk = min_t(size_t, left, sizeof(unsigned long)); + + if (!arch_get_random_long(&v)) + break; + + memcpy(p, &v, chunk); + p += chunk; + left -= chunk; + } + + return nbytes - left; +} +EXPORT_SYMBOL(get_random_bytes_arch); + +enum { + POOL_BITS = BLAKE2S_HASH_SIZE * 8, + POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ +}; + +/* + * Static global variables + */ +static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); + +/********************************************************************** + * + * OS independent entropy store. Here are the functions which handle + * storing entropy in an entropy pool. + * + **********************************************************************/ + +static struct { + struct blake2s_state hash; + spinlock_t lock; + unsigned int entropy_count; +} input_pool = { + .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE), + BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4, + BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 }, + .hash.outlen = BLAKE2S_HASH_SIZE, + .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), +}; + +static void extract_entropy(void *buf, size_t nbytes); +static bool drain_entropy(void *buf, size_t nbytes); + +static void crng_reseed(void); + +/* + * This function adds bytes into the entropy "pool". It does not + * update the entropy estimate. The caller should call + * credit_entropy_bits if this is appropriate. + */ +static void _mix_pool_bytes(const void *in, size_t nbytes) +{ + blake2s_update(&input_pool.hash, in, nbytes); +} + +static void mix_pool_bytes(const void *in, size_t nbytes) +{ + unsigned long flags; + + spin_lock_irqsave(&input_pool.lock, flags); + _mix_pool_bytes(in, nbytes); + spin_unlock_irqrestore(&input_pool.lock, flags); +} + +struct fast_pool { + union { + u32 pool32[4]; + u64 pool64[2]; + }; + unsigned long last; + u16 reg_idx; + u8 count; +}; + +/* + * This is a fast mixing routine used by the interrupt randomness + * collector. It's hardcoded for an 128 bit pool and assumes that any + * locks that might be needed are taken by the caller. + */ +static void fast_mix(u32 pool[4]) +{ + u32 a = pool[0], b = pool[1]; + u32 c = pool[2], d = pool[3]; + + a += b; c += d; + b = rol32(b, 6); d = rol32(d, 27); + d ^= a; b ^= c; - if (!nbytes) - return 0; + a += b; c += d; + b = rol32(b, 16); d = rol32(d, 14); + d ^= a; b ^= c; - len = min_t(size_t, 32, nbytes); - crng_make_state(chacha_state, output, len); + a += b; c += d; + b = rol32(b, 6); d = rol32(d, 27); + d ^= a; b ^= c; - if (copy_to_user(buf, output, len)) - return -EFAULT; - nbytes -= len; - buf += len; - ret += len; + a += b; c += d; + b = rol32(b, 16); d = rol32(d, 14); + d ^= a; b ^= c; - while (nbytes) { - if (large_request && need_resched()) { - if (signal_pending(current)) - break; - schedule(); - } + pool[0] = a; pool[1] = b; + pool[2] = c; pool[3] = d; +} - chacha20_block(chacha_state, output); - if (unlikely(chacha_state[12] == 0)) - ++chacha_state[13]; +static void credit_entropy_bits(size_t nbits) +{ + unsigned int entropy_count, orig, add; - len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE); - if (copy_to_user(buf, output, len)) { - ret = -EFAULT; - break; - } + if (!nbits) + return; - nbytes -= len; - buf += len; - ret += len; - } + add = min_t(size_t, nbits, POOL_BITS); - memzero_explicit(chacha_state, sizeof(chacha_state)); - memzero_explicit(output, sizeof(output)); - return ret; + do { + orig = READ_ONCE(input_pool.entropy_count); + entropy_count = min_t(unsigned int, POOL_BITS, orig + add); + } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); + + if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) + crng_reseed(); } /********************************************************************* @@ -1044,57 +1273,6 @@ static bool drain_entropy(void *buf, size_t nbytes) return true; } -/* - * This function is the exported kernel interface. It returns some - * number of good random numbers, suitable for key generation, seeding - * TCP sequence numbers, etc. It does not rely on the hardware random - * number generator. For random bytes direct from the hardware RNG - * (when available), use get_random_bytes_arch(). In order to ensure - * that the randomness provided by this function is okay, the function - * wait_for_random_bytes() should be called and return 0 at least once - * at any point prior. - */ -static void _get_random_bytes(void *buf, size_t nbytes) -{ - u32 chacha_state[CHACHA_STATE_WORDS]; - u8 tmp[CHACHA_BLOCK_SIZE]; - size_t len; - - if (!nbytes) - return; - - len = min_t(size_t, 32, nbytes); - crng_make_state(chacha_state, buf, len); - nbytes -= len; - buf += len; - - while (nbytes) { - if (nbytes < CHACHA_BLOCK_SIZE) { - chacha20_block(chacha_state, tmp); - memcpy(buf, tmp, nbytes); - memzero_explicit(tmp, sizeof(tmp)); - break; - } - - chacha20_block(chacha_state, buf); - if (unlikely(chacha_state[12] == 0)) - ++chacha_state[13]; - nbytes -= CHACHA_BLOCK_SIZE; - buf += CHACHA_BLOCK_SIZE; - } - - memzero_explicit(chacha_state, sizeof(chacha_state)); -} - -void get_random_bytes(void *buf, size_t nbytes) -{ - static void *previous; - - warn_unseeded_randomness(&previous); - _get_random_bytes(buf, nbytes); -} -EXPORT_SYMBOL(get_random_bytes); - /* * Each time the timer fires, we expect that we got an unpredictable * jump in the cycle counter. Even if the timer is running on another @@ -1144,33 +1322,6 @@ static void try_to_generate_entropy(void) mix_pool_bytes(&stack.now, sizeof(stack.now)); } -/* - * This function will use the architecture-specific hardware random - * number generator if it is available. It is not recommended for - * use. Use get_random_bytes() instead. It returns the number of - * bytes filled in. - */ -size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes) -{ - size_t left = nbytes; - u8 *p = buf; - - while (left) { - unsigned long v; - size_t chunk = min_t(size_t, left, sizeof(unsigned long)); - - if (!arch_get_random_long(&v)) - break; - - memcpy(p, &v, chunk); - p += chunk; - left -= chunk; - } - - return nbytes - left; -} -EXPORT_SYMBOL(get_random_bytes_arch); - static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); static int __init parse_trust_cpu(char *arg) { @@ -1533,129 +1684,6 @@ static int __init random_sysctls_init(void) device_initcall(random_sysctls_init); #endif /* CONFIG_SYSCTL */ -struct batched_entropy { - union { - /* - * We make this 1.5x a ChaCha block, so that we get the - * remaining 32 bytes from fast key erasure, plus one full - * block from the detached ChaCha state. We can increase - * the size of this later if needed so long as we keep the - * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE. - */ - u64 entropy_u64[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u64))]; - u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))]; - }; - local_lock_t lock; - unsigned long generation; - unsigned int position; -}; - -/* - * Get a random word for internal kernel use only. The quality of the random - * number is good as /dev/urandom. In order to ensure that the randomness - * provided by this function is okay, the function wait_for_random_bytes() - * should be called and return 0 at least once at any point prior. - */ -static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = { - .lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock), - .position = UINT_MAX -}; - -u64 get_random_u64(void) -{ - u64 ret; - unsigned long flags; - struct batched_entropy *batch; - static void *previous; - unsigned long next_gen; - - warn_unseeded_randomness(&previous); - - local_lock_irqsave(&batched_entropy_u64.lock, flags); - batch = raw_cpu_ptr(&batched_entropy_u64); - - next_gen = READ_ONCE(base_crng.generation); - if (batch->position >= ARRAY_SIZE(batch->entropy_u64) || - next_gen != batch->generation) { - _get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64)); - batch->position = 0; - batch->generation = next_gen; - } - - ret = batch->entropy_u64[batch->position]; - batch->entropy_u64[batch->position] = 0; - ++batch->position; - local_unlock_irqrestore(&batched_entropy_u64.lock, flags); - return ret; -} -EXPORT_SYMBOL(get_random_u64); - -static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = { - .lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock), - .position = UINT_MAX -}; - -u32 get_random_u32(void) -{ - u32 ret; - unsigned long flags; - struct batched_entropy *batch; - static void *previous; - unsigned long next_gen; - - warn_unseeded_randomness(&previous); - - local_lock_irqsave(&batched_entropy_u32.lock, flags); - batch = raw_cpu_ptr(&batched_entropy_u32); - - next_gen = READ_ONCE(base_crng.generation); - if (batch->position >= ARRAY_SIZE(batch->entropy_u32) || - next_gen != batch->generation) { - _get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32)); - batch->position = 0; - batch->generation = next_gen; - } - - ret = batch->entropy_u32[batch->position]; - batch->entropy_u32[batch->position] = 0; - ++batch->position; - local_unlock_irqrestore(&batched_entropy_u32.lock, flags); - return ret; -} -EXPORT_SYMBOL(get_random_u32); - -/** - * randomize_page - Generate a random, page aligned address - * @start: The smallest acceptable address the caller will take. - * @range: The size of the area, starting at @start, within which the - * random address must fall. - * - * If @start + @range would overflow, @range is capped. - * - * NOTE: Historical use of randomize_range, which this replaces, presumed that - * @start was already page aligned. We now align it regardless. - * - * Return: A page aligned address within [start, start + range). On error, - * @start is returned. - */ -unsigned long randomize_page(unsigned long start, unsigned long range) -{ - if (!PAGE_ALIGNED(start)) { - range -= PAGE_ALIGN(start) - start; - start = PAGE_ALIGN(start); - } - - if (start > ULONG_MAX - range) - range = ULONG_MAX - start; - - range >>= PAGE_SHIFT; - - if (range == 0) - return start; - - return start + (get_random_long() % range << PAGE_SHIFT); -} - /* Interface for in-kernel drivers of true hardware RNGs. * Those devices may produce endless random bits and will be throttled * when our pool is full. -- cgit v1.2.3 From a5ed7cb1a7732ef11959332d507889fbc39ebbb4 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:53:34 +0100 Subject: random: group entropy extraction functions This pulls all of the entropy extraction-focused functions into the third labeled section. No functional changes. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 216 +++++++++++++++++++++++++------------------------- 1 file changed, 109 insertions(+), 107 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 99b55e76b004..ce530a44b4d0 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -895,23 +895,36 @@ size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes) } EXPORT_SYMBOL(get_random_bytes_arch); + +/********************************************************************** + * + * Entropy accumulation and extraction routines. + * + * Callers may add entropy via: + * + * static void mix_pool_bytes(const void *in, size_t nbytes) + * + * After which, if added entropy should be credited: + * + * static void credit_entropy_bits(size_t nbits) + * + * Finally, extract entropy via these two, with the latter one + * setting the entropy count to zero and extracting only if there + * is POOL_MIN_BITS entropy credited prior: + * + * static void extract_entropy(void *buf, size_t nbytes) + * static bool drain_entropy(void *buf, size_t nbytes) + * + **********************************************************************/ + enum { POOL_BITS = BLAKE2S_HASH_SIZE * 8, POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */ }; -/* - * Static global variables - */ +/* For notifying userspace should write into /dev/random. */ static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); -/********************************************************************** - * - * OS independent entropy store. Here are the functions which handle - * storing entropy in an entropy pool. - * - **********************************************************************/ - static struct { struct blake2s_state hash; spinlock_t lock; @@ -924,28 +937,106 @@ static struct { .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock), }; -static void extract_entropy(void *buf, size_t nbytes); -static bool drain_entropy(void *buf, size_t nbytes); - -static void crng_reseed(void); +static void _mix_pool_bytes(const void *in, size_t nbytes) +{ + blake2s_update(&input_pool.hash, in, nbytes); +} /* * This function adds bytes into the entropy "pool". It does not * update the entropy estimate. The caller should call * credit_entropy_bits if this is appropriate. */ -static void _mix_pool_bytes(const void *in, size_t nbytes) +static void mix_pool_bytes(const void *in, size_t nbytes) { - blake2s_update(&input_pool.hash, in, nbytes); + unsigned long flags; + + spin_lock_irqsave(&input_pool.lock, flags); + _mix_pool_bytes(in, nbytes); + spin_unlock_irqrestore(&input_pool.lock, flags); } -static void mix_pool_bytes(const void *in, size_t nbytes) +static void credit_entropy_bits(size_t nbits) +{ + unsigned int entropy_count, orig, add; + + if (!nbits) + return; + + add = min_t(size_t, nbits, POOL_BITS); + + do { + orig = READ_ONCE(input_pool.entropy_count); + entropy_count = min_t(unsigned int, POOL_BITS, orig + add); + } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); + + if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) + crng_reseed(); +} + +/* + * This is an HKDF-like construction for using the hashed collected entropy + * as a PRF key, that's then expanded block-by-block. + */ +static void extract_entropy(void *buf, size_t nbytes) { unsigned long flags; + u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; + struct { + unsigned long rdseed[32 / sizeof(long)]; + size_t counter; + } block; + size_t i; + + for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) { + if (!arch_get_random_seed_long(&block.rdseed[i]) && + !arch_get_random_long(&block.rdseed[i])) + block.rdseed[i] = random_get_entropy(); + } spin_lock_irqsave(&input_pool.lock, flags); - _mix_pool_bytes(in, nbytes); + + /* seed = HASHPRF(last_key, entropy_input) */ + blake2s_final(&input_pool.hash, seed); + + /* next_key = HASHPRF(seed, RDSEED || 0) */ + block.counter = 0; + blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed)); + blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key)); + spin_unlock_irqrestore(&input_pool.lock, flags); + memzero_explicit(next_key, sizeof(next_key)); + + while (nbytes) { + i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE); + /* output = HASHPRF(seed, RDSEED || ++counter) */ + ++block.counter; + blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed)); + nbytes -= i; + buf += i; + } + + memzero_explicit(seed, sizeof(seed)); + memzero_explicit(&block, sizeof(block)); +} + +/* + * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we + * set the entropy count to zero (but don't actually touch any data). Only then + * can we extract a new key with extract_entropy(). + */ +static bool drain_entropy(void *buf, size_t nbytes) +{ + unsigned int entropy_count; + do { + entropy_count = READ_ONCE(input_pool.entropy_count); + if (entropy_count < POOL_MIN_BITS) + return false; + } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); + extract_entropy(buf, nbytes); + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + return true; } struct fast_pool { @@ -988,24 +1079,6 @@ static void fast_mix(u32 pool[4]) pool[2] = c; pool[3] = d; } -static void credit_entropy_bits(size_t nbits) -{ - unsigned int entropy_count, orig, add; - - if (!nbits) - return; - - add = min_t(size_t, nbits, POOL_BITS); - - do { - orig = READ_ONCE(input_pool.entropy_count); - entropy_count = min_t(unsigned int, POOL_BITS, orig + add); - } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); - - if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) - crng_reseed(); -} - /********************************************************************* * * Entropy input management @@ -1202,77 +1275,6 @@ void add_disk_randomness(struct gendisk *disk) EXPORT_SYMBOL_GPL(add_disk_randomness); #endif -/********************************************************************* - * - * Entropy extraction routines - * - *********************************************************************/ - -/* - * This is an HKDF-like construction for using the hashed collected entropy - * as a PRF key, that's then expanded block-by-block. - */ -static void extract_entropy(void *buf, size_t nbytes) -{ - unsigned long flags; - u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE]; - struct { - unsigned long rdseed[32 / sizeof(long)]; - size_t counter; - } block; - size_t i; - - for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) { - if (!arch_get_random_seed_long(&block.rdseed[i]) && - !arch_get_random_long(&block.rdseed[i])) - block.rdseed[i] = random_get_entropy(); - } - - spin_lock_irqsave(&input_pool.lock, flags); - - /* seed = HASHPRF(last_key, entropy_input) */ - blake2s_final(&input_pool.hash, seed); - - /* next_key = HASHPRF(seed, RDSEED || 0) */ - block.counter = 0; - blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed)); - blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key)); - - spin_unlock_irqrestore(&input_pool.lock, flags); - memzero_explicit(next_key, sizeof(next_key)); - - while (nbytes) { - i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE); - /* output = HASHPRF(seed, RDSEED || ++counter) */ - ++block.counter; - blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed)); - nbytes -= i; - buf += i; - } - - memzero_explicit(seed, sizeof(seed)); - memzero_explicit(&block, sizeof(block)); -} - -/* - * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we - * set the entropy count to zero (but don't actually touch any data). Only then - * can we extract a new key with extract_entropy(). - */ -static bool drain_entropy(void *buf, size_t nbytes) -{ - unsigned int entropy_count; - do { - entropy_count = READ_ONCE(input_pool.entropy_count); - if (entropy_count < POOL_MIN_BITS) - return false; - } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); - extract_entropy(buf, nbytes); - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - return true; -} - /* * Each time the timer fires, we expect that we got an unpredictable * jump in the cycle counter. Even if the timer is running on another -- cgit v1.2.3 From 92c653cf14400946f376a29b828d6af7e01f38dd Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:53:34 +0100 Subject: random: group entropy collection functions This pulls all of the entropy collection-focused functions into the fourth labeled section. No functional changes. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 370 ++++++++++++++++++++++++++++---------------------- 1 file changed, 206 insertions(+), 164 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index ce530a44b4d0..75e16e2f07e4 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1039,60 +1039,112 @@ static bool drain_entropy(void *buf, size_t nbytes) return true; } -struct fast_pool { - union { - u32 pool32[4]; - u64 pool64[2]; - }; - unsigned long last; - u16 reg_idx; - u8 count; -}; + +/********************************************************************** + * + * Entropy collection routines. + * + * The following exported functions are used for pushing entropy into + * the above entropy accumulation routines: + * + * void add_device_randomness(const void *buf, size_t size); + * void add_input_randomness(unsigned int type, unsigned int code, + * unsigned int value); + * void add_disk_randomness(struct gendisk *disk); + * void add_hwgenerator_randomness(const void *buffer, size_t count, + * size_t entropy); + * void add_bootloader_randomness(const void *buf, size_t size); + * void add_interrupt_randomness(int irq); + * + * add_device_randomness() adds data to the input pool that + * is likely to differ between two devices (or possibly even per boot). + * This would be things like MAC addresses or serial numbers, or the + * read-out of the RTC. This does *not* credit any actual entropy to + * the pool, but it initializes the pool to different values for devices + * that might otherwise be identical and have very little entropy + * available to them (particularly common in the embedded world). + * + * add_input_randomness() uses the input layer interrupt timing, as well + * as the event type information from the hardware. + * + * add_disk_randomness() uses what amounts to the seek time of block + * layer request events, on a per-disk_devt basis, as input to the + * entropy pool. Note that high-speed solid state drives with very low + * seek times do not make for good sources of entropy, as their seek + * times are usually fairly consistent. + * + * The above two routines try to estimate how many bits of entropy + * to credit. They do this by keeping track of the first and second + * order deltas of the event timings. + * + * add_hwgenerator_randomness() is for true hardware RNGs, and will credit + * entropy as specified by the caller. If the entropy pool is full it will + * block until more entropy is needed. + * + * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or + * add_device_randomness(), depending on whether or not the configuration + * option CONFIG_RANDOM_TRUST_BOOTLOADER is set. + * + * add_interrupt_randomness() uses the interrupt timing as random + * inputs to the entropy pool. Using the cycle counters and the irq source + * as inputs, it feeds the input pool roughly once a second or after 64 + * interrupts, crediting 1 bit of entropy for whichever comes first. + * + **********************************************************************/ + +static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); +static int __init parse_trust_cpu(char *arg) +{ + return kstrtobool(arg, &trust_cpu); +} +early_param("random.trust_cpu", parse_trust_cpu); /* - * This is a fast mixing routine used by the interrupt randomness - * collector. It's hardcoded for an 128 bit pool and assumes that any - * locks that might be needed are taken by the caller. + * The first collection of entropy occurs at system boot while interrupts + * are still turned off. Here we push in RDSEED, a timestamp, and utsname(). + * Depending on the above configuration knob, RDSEED may be considered + * sufficient for initialization. Note that much earlier setup may already + * have pushed entropy into the input pool by the time we get here. */ -static void fast_mix(u32 pool[4]) +int __init rand_initialize(void) { - u32 a = pool[0], b = pool[1]; - u32 c = pool[2], d = pool[3]; - - a += b; c += d; - b = rol32(b, 6); d = rol32(d, 27); - d ^= a; b ^= c; + size_t i; + ktime_t now = ktime_get_real(); + bool arch_init = true; + unsigned long rv; - a += b; c += d; - b = rol32(b, 16); d = rol32(d, 14); - d ^= a; b ^= c; + for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) { + if (!arch_get_random_seed_long_early(&rv) && + !arch_get_random_long_early(&rv)) { + rv = random_get_entropy(); + arch_init = false; + } + mix_pool_bytes(&rv, sizeof(rv)); + } + mix_pool_bytes(&now, sizeof(now)); + mix_pool_bytes(utsname(), sizeof(*(utsname()))); - a += b; c += d; - b = rol32(b, 6); d = rol32(d, 27); - d ^= a; b ^= c; + extract_entropy(base_crng.key, sizeof(base_crng.key)); + ++base_crng.generation; - a += b; c += d; - b = rol32(b, 16); d = rol32(d, 14); - d ^= a; b ^= c; + if (arch_init && trust_cpu && crng_init < 2) { + crng_init = 2; + pr_notice("crng init done (trusting CPU's manufacturer)\n"); + } - pool[0] = a; pool[1] = b; - pool[2] = c; pool[3] = d; + if (ratelimit_disable) { + urandom_warning.interval = 0; + unseeded_warning.interval = 0; + } + return 0; } -/********************************************************************* - * - * Entropy input management - * - *********************************************************************/ - /* There is one of these per entropy source */ struct timer_rand_state { cycles_t last_time; long last_delta, last_delta2; }; -#define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, }; - /* * Add device- or boot-specific data to the input pool to help * initialize it. @@ -1116,8 +1168,6 @@ void add_device_randomness(const void *buf, size_t size) } EXPORT_SYMBOL(add_device_randomness); -static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE; - /* * This function adds entropy to the entropy "pool" by using timing * delays. It uses the timer_rand_state structure to make an estimate @@ -1179,8 +1229,9 @@ void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) { static unsigned char last_value; + static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES }; - /* ignore autorepeat and the like */ + /* Ignore autorepeat and the like. */ if (value == last_value) return; @@ -1190,6 +1241,119 @@ void add_input_randomness(unsigned int type, unsigned int code, } EXPORT_SYMBOL_GPL(add_input_randomness); +#ifdef CONFIG_BLOCK +void add_disk_randomness(struct gendisk *disk) +{ + if (!disk || !disk->random) + return; + /* First major is 1, so we get >= 0x200 here. */ + add_timer_randomness(disk->random, 0x100 + disk_devt(disk)); +} +EXPORT_SYMBOL_GPL(add_disk_randomness); + +void rand_initialize_disk(struct gendisk *disk) +{ + struct timer_rand_state *state; + + /* + * If kzalloc returns null, we just won't use that entropy + * source. + */ + state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL); + if (state) { + state->last_time = INITIAL_JIFFIES; + disk->random = state; + } +} +#endif + +/* + * Interface for in-kernel drivers of true hardware RNGs. + * Those devices may produce endless random bits and will be throttled + * when our pool is full. + */ +void add_hwgenerator_randomness(const void *buffer, size_t count, + size_t entropy) +{ + if (unlikely(crng_init == 0)) { + size_t ret = crng_fast_load(buffer, count); + mix_pool_bytes(buffer, ret); + count -= ret; + buffer += ret; + if (!count || crng_init == 0) + return; + } + + /* + * Throttle writing if we're above the trickle threshold. + * We'll be woken up again once below POOL_MIN_BITS, when + * the calling thread is about to terminate, or once + * CRNG_RESEED_INTERVAL has elapsed. + */ + wait_event_interruptible_timeout(random_write_wait, + !system_wq || kthread_should_stop() || + input_pool.entropy_count < POOL_MIN_BITS, + CRNG_RESEED_INTERVAL); + mix_pool_bytes(buffer, count); + credit_entropy_bits(entropy); +} +EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); + +/* + * Handle random seed passed by bootloader. + * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise + * it would be regarded as device data. + * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER. + */ +void add_bootloader_randomness(const void *buf, size_t size) +{ + if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER)) + add_hwgenerator_randomness(buf, size, size * 8); + else + add_device_randomness(buf, size); +} +EXPORT_SYMBOL_GPL(add_bootloader_randomness); + +struct fast_pool { + union { + u32 pool32[4]; + u64 pool64[2]; + }; + unsigned long last; + u16 reg_idx; + u8 count; +}; + +/* + * This is a fast mixing routine used by the interrupt randomness + * collector. It's hardcoded for an 128 bit pool and assumes that any + * locks that might be needed are taken by the caller. + */ +static void fast_mix(u32 pool[4]) +{ + u32 a = pool[0], b = pool[1]; + u32 c = pool[2], d = pool[3]; + + a += b; c += d; + b = rol32(b, 6); d = rol32(d, 27); + d ^= a; b ^= c; + + a += b; c += d; + b = rol32(b, 16); d = rol32(d, 14); + d ^= a; b ^= c; + + a += b; c += d; + b = rol32(b, 6); d = rol32(d, 27); + d ^= a; b ^= c; + + a += b; c += d; + b = rol32(b, 16); d = rol32(d, 14); + d ^= a; b ^= c; + + pool[0] = a; pool[1] = b; + pool[2] = c; pool[3] = d; +} + static DEFINE_PER_CPU(struct fast_pool, irq_randomness); static u32 get_reg(struct fast_pool *f, struct pt_regs *regs) @@ -1259,22 +1423,11 @@ void add_interrupt_randomness(int irq) fast_pool->count = 0; - /* award one bit for the contents of the fast pool */ + /* Award one bit for the contents of the fast pool. */ credit_entropy_bits(1); } EXPORT_SYMBOL_GPL(add_interrupt_randomness); -#ifdef CONFIG_BLOCK -void add_disk_randomness(struct gendisk *disk) -{ - if (!disk || !disk->random) - return; - /* first major is 1, so we get >= 0x200 here */ - add_timer_randomness(disk->random, 0x100 + disk_devt(disk)); -} -EXPORT_SYMBOL_GPL(add_disk_randomness); -#endif - /* * Each time the timer fires, we expect that we got an unpredictable * jump in the cycle counter. Even if the timer is running on another @@ -1324,73 +1477,6 @@ static void try_to_generate_entropy(void) mix_pool_bytes(&stack.now, sizeof(stack.now)); } -static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); -static int __init parse_trust_cpu(char *arg) -{ - return kstrtobool(arg, &trust_cpu); -} -early_param("random.trust_cpu", parse_trust_cpu); - -/* - * Note that setup_arch() may call add_device_randomness() - * long before we get here. This allows seeding of the pools - * with some platform dependent data very early in the boot - * process. But it limits our options here. We must use - * statically allocated structures that already have all - * initializations complete at compile time. We should also - * take care not to overwrite the precious per platform data - * we were given. - */ -int __init rand_initialize(void) -{ - size_t i; - ktime_t now = ktime_get_real(); - bool arch_init = true; - unsigned long rv; - - for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) { - if (!arch_get_random_seed_long_early(&rv) && - !arch_get_random_long_early(&rv)) { - rv = random_get_entropy(); - arch_init = false; - } - mix_pool_bytes(&rv, sizeof(rv)); - } - mix_pool_bytes(&now, sizeof(now)); - mix_pool_bytes(utsname(), sizeof(*(utsname()))); - - extract_entropy(base_crng.key, sizeof(base_crng.key)); - ++base_crng.generation; - - if (arch_init && trust_cpu && crng_init < 2) { - crng_init = 2; - pr_notice("crng init done (trusting CPU's manufacturer)\n"); - } - - if (ratelimit_disable) { - urandom_warning.interval = 0; - unseeded_warning.interval = 0; - } - return 0; -} - -#ifdef CONFIG_BLOCK -void rand_initialize_disk(struct gendisk *disk) -{ - struct timer_rand_state *state; - - /* - * If kzalloc returns null, we just won't use that entropy - * source. - */ - state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL); - if (state) { - state->last_time = INITIAL_JIFFIES; - disk->random = state; - } -} -#endif - static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { @@ -1685,47 +1771,3 @@ static int __init random_sysctls_init(void) } device_initcall(random_sysctls_init); #endif /* CONFIG_SYSCTL */ - -/* Interface for in-kernel drivers of true hardware RNGs. - * Those devices may produce endless random bits and will be throttled - * when our pool is full. - */ -void add_hwgenerator_randomness(const void *buffer, size_t count, - size_t entropy) -{ - if (unlikely(crng_init == 0)) { - size_t ret = crng_fast_load(buffer, count); - mix_pool_bytes(buffer, ret); - count -= ret; - buffer += ret; - if (!count || crng_init == 0) - return; - } - - /* Throttle writing if we're above the trickle threshold. - * We'll be woken up again once below POOL_MIN_BITS, when - * the calling thread is about to terminate, or once - * CRNG_RESEED_INTERVAL has elapsed. - */ - wait_event_interruptible_timeout(random_write_wait, - !system_wq || kthread_should_stop() || - input_pool.entropy_count < POOL_MIN_BITS, - CRNG_RESEED_INTERVAL); - mix_pool_bytes(buffer, count); - credit_entropy_bits(entropy); -} -EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); - -/* Handle random seed passed by bootloader. - * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise - * it would be regarded as device data. - * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER. - */ -void add_bootloader_randomness(const void *buf, size_t size) -{ - if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER)) - add_hwgenerator_randomness(buf, size, size * 8); - else - add_device_randomness(buf, size); -} -EXPORT_SYMBOL_GPL(add_bootloader_randomness); -- cgit v1.2.3 From a6adf8e7a605250b911e94793fd077933709ff9e Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:53:34 +0100 Subject: random: group userspace read/write functions This pulls all of the userspace read/write-focused functions into the fifth labeled section. No functional changes. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 125 +++++++++++++++++++++++++++++++------------------- 1 file changed, 77 insertions(+), 48 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 75e16e2f07e4..f43d12354c8d 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1477,30 +1477,61 @@ static void try_to_generate_entropy(void) mix_pool_bytes(&stack.now, sizeof(stack.now)); } -static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, - loff_t *ppos) + +/********************************************************************** + * + * Userspace reader/writer interfaces. + * + * getrandom(2) is the primary modern interface into the RNG and should + * be used in preference to anything else. + * + * Reading from /dev/random has the same functionality as calling + * getrandom(2) with flags=0. In earlier versions, however, it had + * vastly different semantics and should therefore be avoided, to + * prevent backwards compatibility issues. + * + * Reading from /dev/urandom has the same functionality as calling + * getrandom(2) with flags=GRND_INSECURE. Because it does not block + * waiting for the RNG to be ready, it should not be used. + * + * Writing to either /dev/random or /dev/urandom adds entropy to + * the input pool but does not credit it. + * + * Polling on /dev/random indicates when the RNG is initialized, on + * the read side, and when it wants new entropy, on the write side. + * + * Both /dev/random and /dev/urandom have the same set of ioctls for + * adding entropy, getting the entropy count, zeroing the count, and + * reseeding the crng. + * + **********************************************************************/ + +SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, + flags) { - static int maxwarn = 10; + if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)) + return -EINVAL; - if (!crng_ready() && maxwarn > 0) { - maxwarn--; - if (__ratelimit(&urandom_warning)) - pr_notice("%s: uninitialized urandom read (%zd bytes read)\n", - current->comm, nbytes); - } + /* + * Requesting insecure and blocking randomness at the same time makes + * no sense. + */ + if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM)) + return -EINVAL; - return get_random_bytes_user(buf, nbytes); -} + if (count > INT_MAX) + count = INT_MAX; -static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, - loff_t *ppos) -{ - int ret; + if (!(flags & GRND_INSECURE) && !crng_ready()) { + int ret; - ret = wait_for_random_bytes(); - if (ret != 0) - return ret; - return get_random_bytes_user(buf, nbytes); + if (flags & GRND_NONBLOCK) + return -EAGAIN; + ret = wait_for_random_bytes(); + if (unlikely(ret)) + return ret; + } + return get_random_bytes_user(buf, count); } static __poll_t random_poll(struct file *file, poll_table *wait) @@ -1552,6 +1583,32 @@ static ssize_t random_write(struct file *file, const char __user *buffer, return (ssize_t)count; } +static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, + loff_t *ppos) +{ + static int maxwarn = 10; + + if (!crng_ready() && maxwarn > 0) { + maxwarn--; + if (__ratelimit(&urandom_warning)) + pr_notice("%s: uninitialized urandom read (%zd bytes read)\n", + current->comm, nbytes); + } + + return get_random_bytes_user(buf, nbytes); +} + +static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, + loff_t *ppos) +{ + int ret; + + ret = wait_for_random_bytes(); + if (ret != 0) + return ret; + return get_random_bytes_user(buf, nbytes); +} + static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) { int size, ent_count; @@ -1560,7 +1617,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) switch (cmd) { case RNDGETENTCNT: - /* inherently racy, no point locking */ + /* Inherently racy, no point locking. */ if (put_user(input_pool.entropy_count, p)) return -EFAULT; return 0; @@ -1636,34 +1693,6 @@ const struct file_operations urandom_fops = { .llseek = noop_llseek, }; -SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int, - flags) -{ - if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)) - return -EINVAL; - - /* - * Requesting insecure and blocking randomness at the same time makes - * no sense. - */ - if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM)) - return -EINVAL; - - if (count > INT_MAX) - count = INT_MAX; - - if (!(flags & GRND_INSECURE) && !crng_ready()) { - int ret; - - if (flags & GRND_NONBLOCK) - return -EAGAIN; - ret = wait_for_random_bytes(); - if (unlikely(ret)) - return ret; - } - return get_random_bytes_user(buf, count); -} - /******************************************************************** * * Sysctl interface -- cgit v1.2.3 From 0deff3c43206c24e746b1410f11125707ad3040e Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:53:34 +0100 Subject: random: group sysctl functions This pulls all of the sysctl-focused functions into the sixth labeled section. No functional changes. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 37 +++++++++++++++++++++++++++++++------ 1 file changed, 31 insertions(+), 6 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index f43d12354c8d..a4b442032db7 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1693,9 +1693,34 @@ const struct file_operations urandom_fops = { .llseek = noop_llseek, }; + /******************************************************************** * - * Sysctl interface + * Sysctl interface. + * + * These are partly unused legacy knobs with dummy values to not break + * userspace and partly still useful things. They are usually accessible + * in /proc/sys/kernel/random/ and are as follows: + * + * - boot_id - a UUID representing the current boot. + * + * - uuid - a random UUID, different each time the file is read. + * + * - poolsize - the number of bits of entropy that the input pool can + * hold, tied to the POOL_BITS constant. + * + * - entropy_avail - the number of bits of entropy currently in the + * input pool. Always <= poolsize. + * + * - write_wakeup_threshold - the amount of entropy in the input pool + * below which write polls to /dev/random will unblock, requesting + * more entropy, tied to the POOL_MIN_BITS constant. It is writable + * to avoid breaking old userspaces, but writing to it does not + * change any behavior of the RNG. + * + * - urandom_min_reseed_secs - fixed to the meaningless value "60". + * It is writable to avoid breaking old userspaces, but writing + * to it does not change any behavior of the RNG. * ********************************************************************/ @@ -1703,8 +1728,8 @@ const struct file_operations urandom_fops = { #include -static int random_min_urandom_seed = 60; -static int random_write_wakeup_bits = POOL_MIN_BITS; +static int sysctl_random_min_urandom_seed = 60; +static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS; static int sysctl_poolsize = POOL_BITS; static char sysctl_bootid[16]; @@ -1761,14 +1786,14 @@ static struct ctl_table random_table[] = { }, { .procname = "write_wakeup_threshold", - .data = &random_write_wakeup_bits, + .data = &sysctl_random_write_wakeup_bits, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec, }, { .procname = "urandom_min_reseed_secs", - .data = &random_min_urandom_seed, + .data = &sysctl_random_min_urandom_seed, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec, @@ -1799,4 +1824,4 @@ static int __init random_sysctls_init(void) return 0; } device_initcall(random_sysctls_init); -#endif /* CONFIG_SYSCTL */ +#endif -- cgit v1.2.3 From 5f75d9f3babea8ae0a2d06724656874f41d317f5 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 12:29:33 +0100 Subject: random: rewrite header introductory comment Now that we've re-documented the various sections, we can remove the outdated text here and replace it with a high-level overview. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 183 ++++++-------------------------------------------- 1 file changed, 21 insertions(+), 162 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index a4b442032db7..e0764e840791 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -2,168 +2,27 @@ /* * Copyright (C) 2017-2022 Jason A. Donenfeld . All Rights Reserved. * Copyright Matt Mackall , 2003, 2004, 2005 - * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All - * rights reserved. - */ - -/* - * Exported interfaces ---- output - * =============================== - * - * There are four exported interfaces; two for use within the kernel, - * and two for use from userspace. - * - * Exported interfaces ---- userspace output - * ----------------------------------------- - * - * The userspace interfaces are two character devices /dev/random and - * /dev/urandom. /dev/random is suitable for use when very high - * quality randomness is desired (for example, for key generation or - * one-time pads), as it will only return a maximum of the number of - * bits of randomness (as estimated by the random number generator) - * contained in the entropy pool. - * - * The /dev/urandom device does not have this limit, and will return - * as many bytes as are requested. As more and more random bytes are - * requested without giving time for the entropy pool to recharge, - * this will result in random numbers that are merely cryptographically - * strong. For many applications, however, this is acceptable. - * - * Exported interfaces ---- kernel output - * -------------------------------------- - * - * The primary kernel interfaces are: - * - * void get_random_bytes(void *buf, size_t nbytes); - * u32 get_random_u32() - * u64 get_random_u64() - * unsigned int get_random_int() - * unsigned long get_random_long() - * - * These interfaces will return the requested number of random bytes - * into the given buffer or as a return value. This is equivalent to a - * read from /dev/urandom. The get_random_{u32,u64,int,long}() family - * of functions may be higher performance for one-off random integers, - * because they do a bit of buffering. - * - * prandom_u32() - * ------------- - * - * For even weaker applications, see the pseudorandom generator - * prandom_u32(), prandom_max(), and prandom_bytes(). If the random - * numbers aren't security-critical at all, these are *far* cheaper. - * Useful for self-tests, random error simulation, randomized backoffs, - * and any other application where you trust that nobody is trying to - * maliciously mess with you by guessing the "random" numbers. - * - * Exported interfaces ---- input - * ============================== - * - * The current exported interfaces for gathering environmental noise - * from the devices are: - * - * void add_device_randomness(const void *buf, size_t size); - * void add_input_randomness(unsigned int type, unsigned int code, - * unsigned int value); - * void add_interrupt_randomness(int irq); - * void add_disk_randomness(struct gendisk *disk); - * void add_hwgenerator_randomness(const void *buffer, size_t count, - * size_t entropy); - * void add_bootloader_randomness(const void *buf, size_t size); - * - * add_device_randomness() is for adding data to the random pool that - * is likely to differ between two devices (or possibly even per boot). - * This would be things like MAC addresses or serial numbers, or the - * read-out of the RTC. This does *not* add any actual entropy to the - * pool, but it initializes the pool to different values for devices - * that might otherwise be identical and have very little entropy - * available to them (particularly common in the embedded world). - * - * add_input_randomness() uses the input layer interrupt timing, as well as - * the event type information from the hardware. - * - * add_interrupt_randomness() uses the interrupt timing as random - * inputs to the entropy pool. Using the cycle counters and the irq source - * as inputs, it feeds the randomness roughly once a second. - * - * add_disk_randomness() uses what amounts to the seek time of block - * layer request events, on a per-disk_devt basis, as input to the - * entropy pool. Note that high-speed solid state drives with very low - * seek times do not make for good sources of entropy, as their seek - * times are usually fairly consistent. - * - * All of these routines try to estimate how many bits of randomness a - * particular randomness source. They do this by keeping track of the - * first and second order deltas of the event timings. - * - * add_hwgenerator_randomness() is for true hardware RNGs, and will credit - * entropy as specified by the caller. If the entropy pool is full it will - * block until more entropy is needed. - * - * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or - * add_device_randomness(), depending on whether or not the configuration - * option CONFIG_RANDOM_TRUST_BOOTLOADER is set. - * - * Ensuring unpredictability at system startup - * ============================================ - * - * When any operating system starts up, it will go through a sequence - * of actions that are fairly predictable by an adversary, especially - * if the start-up does not involve interaction with a human operator. - * This reduces the actual number of bits of unpredictability in the - * entropy pool below the value in entropy_count. In order to - * counteract this effect, it helps to carry information in the - * entropy pool across shut-downs and start-ups. To do this, put the - * following lines an appropriate script which is run during the boot - * sequence: - * - * echo "Initializing random number generator..." - * random_seed=/var/run/random-seed - * # Carry a random seed from start-up to start-up - * # Load and then save the whole entropy pool - * if [ -f $random_seed ]; then - * cat $random_seed >/dev/urandom - * else - * touch $random_seed - * fi - * chmod 600 $random_seed - * dd if=/dev/urandom of=$random_seed count=1 bs=512 - * - * and the following lines in an appropriate script which is run as - * the system is shutdown: - * - * # Carry a random seed from shut-down to start-up - * # Save the whole entropy pool - * echo "Saving random seed..." - * random_seed=/var/run/random-seed - * touch $random_seed - * chmod 600 $random_seed - * dd if=/dev/urandom of=$random_seed count=1 bs=512 - * - * For example, on most modern systems using the System V init - * scripts, such code fragments would be found in - * /etc/rc.d/init.d/random. On older Linux systems, the correct script - * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0. - * - * Effectively, these commands cause the contents of the entropy pool - * to be saved at shut-down time and reloaded into the entropy pool at - * start-up. (The 'dd' in the addition to the bootup script is to - * make sure that /etc/random-seed is different for every start-up, - * even if the system crashes without executing rc.0.) Even with - * complete knowledge of the start-up activities, predicting the state - * of the entropy pool requires knowledge of the previous history of - * the system. - * - * Configuring the /dev/random driver under Linux - * ============================================== - * - * The /dev/random driver under Linux uses minor numbers 8 and 9 of - * the /dev/mem major number (#1). So if your system does not have - * /dev/random and /dev/urandom created already, they can be created - * by using the commands: - * - * mknod /dev/random c 1 8 - * mknod /dev/urandom c 1 9 + * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All rights reserved. + * + * This driver produces cryptographically secure pseudorandom data. It is divided + * into roughly six sections, each with a section header: + * + * - Initialization and readiness waiting. + * - Fast key erasure RNG, the "crng". + * - Entropy accumulation and extraction routines. + * - Entropy collection routines. + * - Userspace reader/writer interfaces. + * - Sysctl interface. + * + * The high level overview is that there is one input pool, into which + * various pieces of data are hashed. Some of that data is then "credited" as + * having a certain number of bits of entropy. When enough bits of entropy are + * available, the hash is finalized and handed as a key to a stream cipher that + * expands it indefinitely for various consumers. This key is periodically + * refreshed as the various entropy collectors, described below, add data to the + * input pool and credit it. There is currently no Fortuna-like scheduler + * involved, which can lead to malicious entropy sources causing a premature + * reseed, and the entropy estimates are, at best, conservative guesses. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt -- cgit v1.2.3 From 58340f8e952b613e0ead0bed58b97b05bf4743c5 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 4 Feb 2022 16:15:46 +0100 Subject: random: defer fast pool mixing to worker MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On PREEMPT_RT, it's problematic to take spinlocks from hard irq handlers. We can fix this by deferring to a workqueue the dumping of the fast pool into the input pool. We accomplish this with some careful rules on fast_pool->count: - When it's incremented to >= 64, we schedule the work. - If the top bit is set, we never schedule the work, even if >= 64. - The worker is responsible for setting it back to 0 when it's done. There are two small issues around using workqueues for this purpose that we work around. The first issue is that mix_interrupt_randomness() might be migrated to another CPU during CPU hotplug. This issue is rectified by checking that it hasn't been migrated (after disabling irqs). If it has been migrated, then we set the count to zero, so that when the CPU comes online again, it can requeue the work. As part of this, we switch to using an atomic_t, so that the increment in the irq handler doesn't wipe out the zeroing if the CPU comes back online while this worker is running. The second issue is that, though relatively minor in effect, we probably want to make sure we get a consistent view of the pool onto the stack, in case it's interrupted by an irq while reading. To do this, we don't reenable irqs until after the copy. There are only 18 instructions between the cli and sti, so this is a pretty tiny window. Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Theodore Ts'o Cc: Jonathan NeuschĂ€fer Acked-by: Sebastian Andrzej Siewior Reviewed-by: Sultan Alsawaf Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 63 +++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 49 insertions(+), 14 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index e0764e840791..26cbfcaa3b78 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1178,9 +1178,10 @@ struct fast_pool { u32 pool32[4]; u64 pool64[2]; }; + struct work_struct mix; unsigned long last; + atomic_t count; u16 reg_idx; - u8 count; }; /* @@ -1230,12 +1231,49 @@ static u32 get_reg(struct fast_pool *f, struct pt_regs *regs) return *ptr; } +static void mix_interrupt_randomness(struct work_struct *work) +{ + struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix); + u32 pool[4]; + + /* Check to see if we're running on the wrong CPU due to hotplug. */ + local_irq_disable(); + if (fast_pool != this_cpu_ptr(&irq_randomness)) { + local_irq_enable(); + /* + * If we are unlucky enough to have been moved to another CPU, + * during CPU hotplug while the CPU was shutdown then we set + * our count to zero atomically so that when the CPU comes + * back online, it can enqueue work again. The _release here + * pairs with the atomic_inc_return_acquire in + * add_interrupt_randomness(). + */ + atomic_set_release(&fast_pool->count, 0); + return; + } + + /* + * Copy the pool to the stack so that the mixer always has a + * consistent view, before we reenable irqs again. + */ + memcpy(pool, fast_pool->pool32, sizeof(pool)); + atomic_set(&fast_pool->count, 0); + fast_pool->last = jiffies; + local_irq_enable(); + + mix_pool_bytes(pool, sizeof(pool)); + credit_entropy_bits(1); + memzero_explicit(pool, sizeof(pool)); +} + void add_interrupt_randomness(int irq) { + enum { MIX_INFLIGHT = 1U << 31 }; struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness); struct pt_regs *regs = get_irq_regs(); unsigned long now = jiffies; cycles_t cycles = random_get_entropy(); + unsigned int new_count; if (cycles == 0) cycles = get_reg(fast_pool, regs); @@ -1255,12 +1293,13 @@ void add_interrupt_randomness(int irq) } fast_mix(fast_pool->pool32); - ++fast_pool->count; + /* The _acquire here pairs with the atomic_set_release in mix_interrupt_randomness(). */ + new_count = (unsigned int)atomic_inc_return_acquire(&fast_pool->count); if (unlikely(crng_init == 0)) { - if (fast_pool->count >= 64 && + if (new_count >= 64 && crng_fast_load(fast_pool->pool32, sizeof(fast_pool->pool32)) > 0) { - fast_pool->count = 0; + atomic_set(&fast_pool->count, 0); fast_pool->last = now; if (spin_trylock(&input_pool.lock)) { _mix_pool_bytes(&fast_pool->pool32, sizeof(fast_pool->pool32)); @@ -1270,20 +1309,16 @@ void add_interrupt_randomness(int irq) return; } - if ((fast_pool->count < 64) && !time_after(now, fast_pool->last + HZ)) + if (new_count & MIX_INFLIGHT) return; - if (!spin_trylock(&input_pool.lock)) + if (new_count < 64 && !time_after(now, fast_pool->last + HZ)) return; - fast_pool->last = now; - _mix_pool_bytes(&fast_pool->pool32, sizeof(fast_pool->pool32)); - spin_unlock(&input_pool.lock); - - fast_pool->count = 0; - - /* Award one bit for the contents of the fast pool. */ - credit_entropy_bits(1); + if (unlikely(!fast_pool->mix.func)) + INIT_WORK(&fast_pool->mix, mix_interrupt_randomness); + atomic_or(MIX_INFLIGHT, &fast_pool->count); + queue_work_on(raw_smp_processor_id(), system_highpri_wq, &fast_pool->mix); } EXPORT_SYMBOL_GPL(add_interrupt_randomness); -- cgit v1.2.3 From afba0b80b977b2a8f16234f2acd982f82710ba33 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sat, 12 Feb 2022 01:26:17 +0100 Subject: random: do not take pool spinlock at boot Since rand_initialize() is run while interrupts are still off and nothing else is running, we don't need to repeatedly take and release the pool spinlock, especially in the RDSEED loop. Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 26cbfcaa3b78..0541066e2e5c 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -978,10 +978,10 @@ int __init rand_initialize(void) rv = random_get_entropy(); arch_init = false; } - mix_pool_bytes(&rv, sizeof(rv)); + _mix_pool_bytes(&rv, sizeof(rv)); } - mix_pool_bytes(&now, sizeof(now)); - mix_pool_bytes(utsname(), sizeof(*(utsname()))); + _mix_pool_bytes(&now, sizeof(now)); + _mix_pool_bytes(utsname(), sizeof(*(utsname()))); extract_entropy(base_crng.key, sizeof(base_crng.key)); ++base_crng.generation; -- cgit v1.2.3 From da792c6d5f59a76c10a310c5d4c93428fd18f996 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sat, 12 Feb 2022 23:54:09 +0100 Subject: random: unify early init crng load accounting crng_fast_load() and crng_slow_load() have different semantics: - crng_fast_load() xors and accounts with crng_init_cnt. - crng_slow_load() hashes and doesn't account. However add_hwgenerator_randomness() can afford to hash (it's called from a kthread), and it should account. Additionally, ones that can afford to hash don't need to take a trylock but can take a normal lock. So, we combine these into one function, crng_pre_init_inject(), which allows us to control these in a uniform way. This will make it simpler later to simplify this all down when the time comes for that. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 112 ++++++++++++++++++++++++++------------------------ 1 file changed, 58 insertions(+), 54 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 0541066e2e5c..93d01f918720 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -386,7 +386,7 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], * For the fast path, we check whether we're ready, unlocked first, and * then re-check once locked later. In the case where we're really not * ready, we do fast key erasure with the base_crng directly, because - * this is what crng_{fast,slow}_load mutate during early init. + * this is what crng_pre_init_inject() mutates during early init. */ if (unlikely(!crng_ready())) { bool ready; @@ -437,72 +437,75 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], } /* - * This function is for crng_init == 0 only. - * - * crng_fast_load() can be called by code in the interrupt service - * path. So we can't afford to dilly-dally. Returns the number of - * bytes processed from cp. + * This function is for crng_init == 0 only. It loads entropy directly + * into the crng's key, without going through the input pool. It is, + * generally speaking, not very safe, but we use this only at early + * boot time when it's better to have something there rather than + * nothing. + * + * There are two paths, a slow one and a fast one. The slow one + * hashes the input along with the current key. The fast one simply + * xors it in, and should only be used from interrupt context. + * + * If account is set, then the crng_init_cnt counter is incremented. + * This shouldn't be set by functions like add_device_randomness(), + * where we can't trust the buffer passed to it is guaranteed to be + * unpredictable (so it might not have any entropy at all). + * + * Returns the number of bytes processed from input, which is bounded + * by CRNG_INIT_CNT_THRESH if account is true. */ -static size_t crng_fast_load(const void *cp, size_t len) +static size_t crng_pre_init_inject(const void *input, size_t len, + bool fast, bool account) { static int crng_init_cnt = 0; unsigned long flags; - const u8 *src = (const u8 *)cp; - size_t ret = 0; - if (!spin_trylock_irqsave(&base_crng.lock, flags)) - return 0; + if (fast) { + if (!spin_trylock_irqsave(&base_crng.lock, flags)) + return 0; + } else { + spin_lock_irqsave(&base_crng.lock, flags); + } + if (crng_init != 0) { spin_unlock_irqrestore(&base_crng.lock, flags); return 0; } - while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) { - base_crng.key[crng_init_cnt % sizeof(base_crng.key)] ^= *src; - src++; crng_init_cnt++; len--; ret++; - } - if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { - ++base_crng.generation; - crng_init = 1; - } - spin_unlock_irqrestore(&base_crng.lock, flags); - if (crng_init == 1) - pr_notice("fast init done\n"); - return ret; -} -/* - * This function is for crng_init == 0 only. - * - * crng_slow_load() is called by add_device_randomness, which has two - * attributes. (1) We can't trust the buffer passed to it is - * guaranteed to be unpredictable (so it might not have any entropy at - * all), and (2) it doesn't have the performance constraints of - * crng_fast_load(). - * - * So, we simply hash the contents in with the current key. Finally, - * we do *not* advance crng_init_cnt since buffer we may get may be - * something like a fixed DMI table (for example), which might very - * well be unique to the machine, but is otherwise unvarying. - */ -static void crng_slow_load(const void *cp, size_t len) -{ - unsigned long flags; - struct blake2s_state hash; + if (account) + len = min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt); - blake2s_init(&hash, sizeof(base_crng.key)); + if (fast) { + const u8 *src = input; + size_t i; - if (!spin_trylock_irqsave(&base_crng.lock, flags)) - return; - if (crng_init != 0) { - spin_unlock_irqrestore(&base_crng.lock, flags); - return; + for (i = 0; i < len; ++i) + base_crng.key[(crng_init_cnt + i) % + sizeof(base_crng.key)] ^= src[i]; + } else { + struct blake2s_state hash; + + blake2s_init(&hash, sizeof(base_crng.key)); + blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); + blake2s_update(&hash, input, len); + blake2s_final(&hash, base_crng.key); } - blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); - blake2s_update(&hash, cp, len); - blake2s_final(&hash, base_crng.key); + if (account) { + crng_init_cnt += len; + if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { + ++base_crng.generation; + crng_init = 1; + } + } spin_unlock_irqrestore(&base_crng.lock, flags); + + if (crng_init == 1) + pr_notice("fast init done\n"); + + return len; } static void _get_random_bytes(void *buf, size_t nbytes) @@ -1018,7 +1021,7 @@ void add_device_randomness(const void *buf, size_t size) unsigned long flags; if (!crng_ready() && size) - crng_slow_load(buf, size); + crng_pre_init_inject(buf, size, false, false); spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(buf, size); @@ -1135,7 +1138,7 @@ void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy) { if (unlikely(crng_init == 0)) { - size_t ret = crng_fast_load(buffer, count); + size_t ret = crng_pre_init_inject(buffer, count, false, true); mix_pool_bytes(buffer, ret); count -= ret; buffer += ret; @@ -1298,7 +1301,8 @@ void add_interrupt_randomness(int irq) if (unlikely(crng_init == 0)) { if (new_count >= 64 && - crng_fast_load(fast_pool->pool32, sizeof(fast_pool->pool32)) > 0) { + crng_pre_init_inject(fast_pool->pool32, sizeof(fast_pool->pool32), + true, true) > 0) { atomic_set(&fast_pool->count, 0); fast_pool->last = now; if (spin_trylock(&input_pool.lock)) { -- cgit v1.2.3 From 1daf2f387652bf3a7044aea042f5023b3f6b189b Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sat, 12 Feb 2022 23:57:38 +0100 Subject: random: check for crng_init == 0 in add_device_randomness() This has no real functional change, as crng_pre_init_inject() (and before that, crng_slow_init()) always checks for == 0, not >= 2. So correct the outer unlocked change to reflect that. Before this used crng_ready(), which was not correct. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 93d01f918720..bca4467e540f 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1020,7 +1020,7 @@ void add_device_randomness(const void *buf, size_t size) unsigned long time = random_get_entropy() ^ jiffies; unsigned long flags; - if (!crng_ready() && size) + if (crng_init == 0 && size) crng_pre_init_inject(buf, size, false, false); spin_lock_irqsave(&input_pool.lock, flags); -- cgit v1.2.3 From b777c38239fec5a528e59f55b379e31b1a187524 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sun, 13 Feb 2022 16:17:01 +0100 Subject: random: pull add_hwgenerator_randomness() declaration into random.h add_hwgenerator_randomness() is a function implemented and documented inside of random.c. It is the way that hardware RNGs push data into it. Therefore, it should be declared in random.h. Otherwise sparse complains with: random.c:1137:6: warning: symbol 'add_hwgenerator_randomness' was not declared. Should it be static? The alternative would be to include hw_random.h into random.c, but that wouldn't really be good for anything except slowing down compile time. Cc: Matt Mackall Cc: Theodore Ts'o Acked-by: Herbert Xu Reviewed-by: Eric Biggers Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/hw_random/core.c | 1 + include/linux/hw_random.h | 2 -- include/linux/random.h | 2 ++ 3 files changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index a3db27916256..cfb085de876b 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include #include diff --git a/include/linux/hw_random.h b/include/linux/hw_random.h index 1a9fc38f8938..aa1d4da03538 100644 --- a/include/linux/hw_random.h +++ b/include/linux/hw_random.h @@ -60,7 +60,5 @@ extern int devm_hwrng_register(struct device *dev, struct hwrng *rng); /** Unregister a Hardware Random Number Generator driver. */ extern void hwrng_unregister(struct hwrng *rng); extern void devm_hwrng_unregister(struct device *dve, struct hwrng *rng); -/** Feed random bits into the pool. */ -extern void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy); #endif /* LINUX_HWRANDOM_H_ */ diff --git a/include/linux/random.h b/include/linux/random.h index 37e1e8c43d7e..d7354de9351e 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -32,6 +32,8 @@ static inline void add_latent_entropy(void) {} extern void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) __latent_entropy; extern void add_interrupt_randomness(int irq) __latent_entropy; +extern void add_hwgenerator_randomness(const void *buffer, size_t count, + size_t entropy); extern void get_random_bytes(void *buf, size_t nbytes); extern int wait_for_random_bytes(void); -- cgit v1.2.3 From 3191dd5a1179ef0fad5a050a1702ae98b6251e8f Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sun, 13 Feb 2022 22:48:04 +0100 Subject: random: clear fast pool, crng, and batches in cpuhp bring up For the irq randomness fast pool, rather than having to use expensive atomics, which were visibly the most expensive thing in the entire irq handler, simply take care of the extreme edge case of resetting count to zero in the cpuhp online handler, just after workqueues have been reenabled. This simplifies the code a bit and lets us use vanilla variables rather than atomics, and performance should be improved. As well, very early on when the CPU comes up, while interrupts are still disabled, we clear out the per-cpu crng and its batches, so that it always starts with fresh randomness. Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Theodore Ts'o Cc: Sultan Alsawaf Cc: Dominik Brodowski Acked-by: Sebastian Andrzej Siewior Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 62 +++++++++++++++++++++++++++++++++++----------- include/linux/cpuhotplug.h | 2 ++ include/linux/random.h | 5 ++++ kernel/cpu.c | 11 ++++++++ 4 files changed, 65 insertions(+), 15 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index bca4467e540f..d73a75cbe82d 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -698,6 +698,25 @@ u32 get_random_u32(void) } EXPORT_SYMBOL(get_random_u32); +#ifdef CONFIG_SMP +/* + * This function is called when the CPU is coming up, with entry + * CPUHP_RANDOM_PREPARE, which comes before CPUHP_WORKQUEUE_PREP. + */ +int random_prepare_cpu(unsigned int cpu) +{ + /* + * When the cpu comes back online, immediately invalidate both + * the per-cpu crng and all batches, so that we serve fresh + * randomness. + */ + per_cpu_ptr(&crngs, cpu)->generation = ULONG_MAX; + per_cpu_ptr(&batched_entropy_u32, cpu)->position = UINT_MAX; + per_cpu_ptr(&batched_entropy_u64, cpu)->position = UINT_MAX; + return 0; +} +#endif + /** * randomize_page - Generate a random, page aligned address * @start: The smallest acceptable address the caller will take. @@ -1183,7 +1202,7 @@ struct fast_pool { }; struct work_struct mix; unsigned long last; - atomic_t count; + unsigned int count; u16 reg_idx; }; @@ -1219,6 +1238,29 @@ static void fast_mix(u32 pool[4]) static DEFINE_PER_CPU(struct fast_pool, irq_randomness); +#ifdef CONFIG_SMP +/* + * This function is called when the CPU has just come online, with + * entry CPUHP_AP_RANDOM_ONLINE, just after CPUHP_AP_WORKQUEUE_ONLINE. + */ +int random_online_cpu(unsigned int cpu) +{ + /* + * During CPU shutdown and before CPU onlining, add_interrupt_ + * randomness() may schedule mix_interrupt_randomness(), and + * set the MIX_INFLIGHT flag. However, because the worker can + * be scheduled on a different CPU during this period, that + * flag will never be cleared. For that reason, we zero out + * the flag here, which runs just after workqueues are onlined + * for the CPU again. This also has the effect of setting the + * irq randomness count to zero so that new accumulated irqs + * are fresh. + */ + per_cpu_ptr(&irq_randomness, cpu)->count = 0; + return 0; +} +#endif + static u32 get_reg(struct fast_pool *f, struct pt_regs *regs) { u32 *ptr = (u32 *)regs; @@ -1243,15 +1285,6 @@ static void mix_interrupt_randomness(struct work_struct *work) local_irq_disable(); if (fast_pool != this_cpu_ptr(&irq_randomness)) { local_irq_enable(); - /* - * If we are unlucky enough to have been moved to another CPU, - * during CPU hotplug while the CPU was shutdown then we set - * our count to zero atomically so that when the CPU comes - * back online, it can enqueue work again. The _release here - * pairs with the atomic_inc_return_acquire in - * add_interrupt_randomness(). - */ - atomic_set_release(&fast_pool->count, 0); return; } @@ -1260,7 +1293,7 @@ static void mix_interrupt_randomness(struct work_struct *work) * consistent view, before we reenable irqs again. */ memcpy(pool, fast_pool->pool32, sizeof(pool)); - atomic_set(&fast_pool->count, 0); + fast_pool->count = 0; fast_pool->last = jiffies; local_irq_enable(); @@ -1296,14 +1329,13 @@ void add_interrupt_randomness(int irq) } fast_mix(fast_pool->pool32); - /* The _acquire here pairs with the atomic_set_release in mix_interrupt_randomness(). */ - new_count = (unsigned int)atomic_inc_return_acquire(&fast_pool->count); + new_count = ++fast_pool->count; if (unlikely(crng_init == 0)) { if (new_count >= 64 && crng_pre_init_inject(fast_pool->pool32, sizeof(fast_pool->pool32), true, true) > 0) { - atomic_set(&fast_pool->count, 0); + fast_pool->count = 0; fast_pool->last = now; if (spin_trylock(&input_pool.lock)) { _mix_pool_bytes(&fast_pool->pool32, sizeof(fast_pool->pool32)); @@ -1321,7 +1353,7 @@ void add_interrupt_randomness(int irq) if (unlikely(!fast_pool->mix.func)) INIT_WORK(&fast_pool->mix, mix_interrupt_randomness); - atomic_or(MIX_INFLIGHT, &fast_pool->count); + fast_pool->count |= MIX_INFLIGHT; queue_work_on(raw_smp_processor_id(), system_highpri_wq, &fast_pool->mix); } EXPORT_SYMBOL_GPL(add_interrupt_randomness); diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h index 411a428ace4d..481e565cc5c4 100644 --- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h @@ -100,6 +100,7 @@ enum cpuhp_state { CPUHP_AP_ARM_CACHE_B15_RAC_DEAD, CPUHP_PADATA_DEAD, CPUHP_AP_DTPM_CPU_DEAD, + CPUHP_RANDOM_PREPARE, CPUHP_WORKQUEUE_PREP, CPUHP_POWER_NUMA_PREPARE, CPUHP_HRTIMERS_PREPARE, @@ -240,6 +241,7 @@ enum cpuhp_state { CPUHP_AP_PERF_CSKY_ONLINE, CPUHP_AP_WATCHDOG_ONLINE, CPUHP_AP_WORKQUEUE_ONLINE, + CPUHP_AP_RANDOM_ONLINE, CPUHP_AP_RCUTREE_ONLINE, CPUHP_AP_BASE_CACHEINFO_ONLINE, CPUHP_AP_ONLINE_DYN, diff --git a/include/linux/random.h b/include/linux/random.h index d7354de9351e..6148b8d1ccf3 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -156,4 +156,9 @@ static inline bool __init arch_get_random_long_early(unsigned long *v) } #endif +#ifdef CONFIG_SMP +extern int random_prepare_cpu(unsigned int cpu); +extern int random_online_cpu(unsigned int cpu); +#endif + #endif /* _LINUX_RANDOM_H */ diff --git a/kernel/cpu.c b/kernel/cpu.c index 407a2568f35e..238cba15449f 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -34,6 +34,7 @@ #include #include #include +#include #include #define CREATE_TRACE_POINTS @@ -1659,6 +1660,11 @@ static struct cpuhp_step cpuhp_hp_states[] = { .startup.single = perf_event_init_cpu, .teardown.single = perf_event_exit_cpu, }, + [CPUHP_RANDOM_PREPARE] = { + .name = "random:prepare", + .startup.single = random_prepare_cpu, + .teardown.single = NULL, + }, [CPUHP_WORKQUEUE_PREP] = { .name = "workqueue:prepare", .startup.single = workqueue_prepare_cpu, @@ -1782,6 +1788,11 @@ static struct cpuhp_step cpuhp_hp_states[] = { .startup.single = workqueue_online_cpu, .teardown.single = workqueue_offline_cpu, }, + [CPUHP_AP_RANDOM_ONLINE] = { + .name = "random:online", + .startup.single = random_online_cpu, + .teardown.single = NULL, + }, [CPUHP_AP_RCUTREE_ONLINE] = { .name = "RCU/tree:online", .startup.single = rcutree_online_cpu, -- cgit v1.2.3 From da3951ebdcd1cb1d5c750e08cd05aee7b0c04d9a Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 22 Feb 2022 13:46:10 +0100 Subject: random: round-robin registers as ulong, not u32 When the interrupt handler does not have a valid cycle counter, it calls get_reg() to read a register from the irq stack, in round-robin. Currently it does this assuming that registers are 32-bit. This is _probably_ the case, and probably all platforms without cycle counters are in fact 32-bit platforms. But maybe not, and either way, it's not quite correct. This commit fixes that to deal with `unsigned long` rather than `u32`. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index d73a75cbe82d..a4dedeea35e9 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1261,15 +1261,15 @@ int random_online_cpu(unsigned int cpu) } #endif -static u32 get_reg(struct fast_pool *f, struct pt_regs *regs) +static unsigned long get_reg(struct fast_pool *f, struct pt_regs *regs) { - u32 *ptr = (u32 *)regs; + unsigned long *ptr = (unsigned long *)regs; unsigned int idx; if (regs == NULL) return 0; idx = READ_ONCE(f->reg_idx); - if (idx >= sizeof(struct pt_regs) / sizeof(u32)) + if (idx >= sizeof(struct pt_regs) / sizeof(unsigned long)) idx = 0; ptr += idx++; WRITE_ONCE(f->reg_idx, idx); -- cgit v1.2.3 From a3f9e8910e1584d7725ef7d5ac870920d42d0bb4 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 22 Feb 2022 14:01:57 +0100 Subject: random: only wake up writers after zap if threshold was passed The only time that we need to wake up /dev/random writers on RNDCLEARPOOL/RNDZAPPOOL is when we're changing from a value that is greater than or equal to POOL_MIN_BITS to zero, because if we're changing from below POOL_MIN_BITS to zero, the writers are already unblocked. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index a4dedeea35e9..536237a0f073 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1582,7 +1582,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; - if (xchg(&input_pool.entropy_count, 0)) { + if (xchg(&input_pool.entropy_count, 0) >= POOL_MIN_BITS) { wake_up_interruptible(&random_write_wait); kill_fasync(&fasync, SIGIO, POLL_OUT); } -- cgit v1.2.3 From 64276a9939ff414f2f0db38036cf4e1a0a703394 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 24 Feb 2022 23:04:56 +0100 Subject: random: cleanup UUID handling Rather than hard coding various lengths, we can use the right constants. Strings should be `char *` while buffers should be `u8 *`. Rather than have a nonsensical and unused maxlength, just remove it. Finally, use snprintf instead of sprintf, just out of good hygiene. As well, remove the old comment about returning a binary UUID via the binary sysctl syscall. That syscall was removed from the kernel in 5.5, and actually, the "uuid_strategy" function and related infrastructure for even serving it via the binary sysctl syscall was removed with 894d2491153a ("sysctl drivers: Remove dead binary sysctl support") back in 2.6.33. Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 536237a0f073..4cdf39567bae 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1661,22 +1661,25 @@ const struct file_operations urandom_fops = { static int sysctl_random_min_urandom_seed = 60; static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS; static int sysctl_poolsize = POOL_BITS; -static char sysctl_bootid[16]; +static u8 sysctl_bootid[UUID_SIZE]; /* * This function is used to return both the bootid UUID, and random - * UUID. The difference is in whether table->data is NULL; if it is, + * UUID. The difference is in whether table->data is NULL; if it is, * then a new UUID is generated and returned to the user. - * - * If the user accesses this via the proc interface, the UUID will be - * returned as an ASCII string in the standard UUID format; if via the - * sysctl system call, as 16 bytes of binary data. */ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { - struct ctl_table fake_table; - unsigned char buf[64], tmp_uuid[16], *uuid; + u8 tmp_uuid[UUID_SIZE], *uuid; + char uuid_string[UUID_STRING_LEN + 1]; + struct ctl_table fake_table = { + .data = uuid_string, + .maxlen = UUID_STRING_LEN + }; + + if (write) + return -EPERM; uuid = table->data; if (!uuid) { @@ -1691,12 +1694,8 @@ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer, spin_unlock(&bootid_spinlock); } - sprintf(buf, "%pU", uuid); - - fake_table.data = buf; - fake_table.maxlen = sizeof(buf); - - return proc_dostring(&fake_table, write, buffer, lenp, ppos); + snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid); + return proc_dostring(&fake_table, 0, buffer, lenp, ppos); } static struct ctl_table random_table[] = { @@ -1731,13 +1730,11 @@ static struct ctl_table random_table[] = { { .procname = "boot_id", .data = &sysctl_bootid, - .maxlen = 16, .mode = 0444, .proc_handler = proc_do_uuid, }, { .procname = "uuid", - .maxlen = 16, .mode = 0444, .proc_handler = proc_do_uuid, }, -- cgit v1.2.3 From abded93ec1e9692920fe309f07f40bd1035f2940 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 24 Feb 2022 18:30:58 +0100 Subject: random: unify cycles_t and jiffies usage and types random_get_entropy() returns a cycles_t, not an unsigned long, which is sometimes 64 bits on various 32-bit platforms, including x86. Conversely, jiffies is always unsigned long. This commit fixes things to use cycles_t for fields that use random_get_entropy(), named "cycles", and unsigned long for fields that use jiffies, named "now". It's also good to mix in a cycles_t and a jiffies in the same way for both add_device_randomness and add_timer_randomness, rather than using xor in one case. Finally, we unify the order of these volatile reads, always reading the more precise cycles counter, and then jiffies, so that the cycle counter is as close to the event as possible. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 56 +++++++++++++++++++++++++-------------------------- 1 file changed, 27 insertions(+), 29 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 4cdf39567bae..3b83a6ac9f59 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1020,12 +1020,6 @@ int __init rand_initialize(void) return 0; } -/* There is one of these per entropy source */ -struct timer_rand_state { - cycles_t last_time; - long last_delta, last_delta2; -}; - /* * Add device- or boot-specific data to the input pool to help * initialize it. @@ -1036,19 +1030,26 @@ struct timer_rand_state { */ void add_device_randomness(const void *buf, size_t size) { - unsigned long time = random_get_entropy() ^ jiffies; - unsigned long flags; + cycles_t cycles = random_get_entropy(); + unsigned long flags, now = jiffies; if (crng_init == 0 && size) crng_pre_init_inject(buf, size, false, false); spin_lock_irqsave(&input_pool.lock, flags); + _mix_pool_bytes(&cycles, sizeof(cycles)); + _mix_pool_bytes(&now, sizeof(now)); _mix_pool_bytes(buf, size); - _mix_pool_bytes(&time, sizeof(time)); spin_unlock_irqrestore(&input_pool.lock, flags); } EXPORT_SYMBOL(add_device_randomness); +/* There is one of these per entropy source */ +struct timer_rand_state { + unsigned long last_time; + long last_delta, last_delta2; +}; + /* * This function adds entropy to the entropy "pool" by using timing * delays. It uses the timer_rand_state structure to make an estimate @@ -1057,29 +1058,26 @@ EXPORT_SYMBOL(add_device_randomness); * The number "num" is also added to the pool - it should somehow describe * the type of event which just happened. This is currently 0-255 for * keyboard scan codes, and 256 upwards for interrupts. - * */ static void add_timer_randomness(struct timer_rand_state *state, unsigned int num) { - struct { - long jiffies; - unsigned int cycles; - unsigned int num; - } sample; + cycles_t cycles = random_get_entropy(); + unsigned long flags, now = jiffies; long delta, delta2, delta3; - sample.jiffies = jiffies; - sample.cycles = random_get_entropy(); - sample.num = num; - mix_pool_bytes(&sample, sizeof(sample)); + spin_lock_irqsave(&input_pool.lock, flags); + _mix_pool_bytes(&cycles, sizeof(cycles)); + _mix_pool_bytes(&now, sizeof(now)); + _mix_pool_bytes(&num, sizeof(num)); + spin_unlock_irqrestore(&input_pool.lock, flags); /* * Calculate number of bits of randomness we probably added. * We take into account the first, second and third-order deltas * in order to make our estimate. */ - delta = sample.jiffies - READ_ONCE(state->last_time); - WRITE_ONCE(state->last_time, sample.jiffies); + delta = now - READ_ONCE(state->last_time); + WRITE_ONCE(state->last_time, now); delta2 = delta - READ_ONCE(state->last_delta); WRITE_ONCE(state->last_delta, delta); @@ -1305,10 +1303,10 @@ static void mix_interrupt_randomness(struct work_struct *work) void add_interrupt_randomness(int irq) { enum { MIX_INFLIGHT = 1U << 31 }; + cycles_t cycles = random_get_entropy(); + unsigned long now = jiffies; struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness); struct pt_regs *regs = get_irq_regs(); - unsigned long now = jiffies; - cycles_t cycles = random_get_entropy(); unsigned int new_count; if (cycles == 0) @@ -1383,28 +1381,28 @@ static void entropy_timer(struct timer_list *t) static void try_to_generate_entropy(void) { struct { - unsigned long now; + cycles_t cycles; struct timer_list timer; } stack; - stack.now = random_get_entropy(); + stack.cycles = random_get_entropy(); /* Slow counter - or none. Don't even bother */ - if (stack.now == random_get_entropy()) + if (stack.cycles == random_get_entropy()) return; timer_setup_on_stack(&stack.timer, entropy_timer, 0); while (!crng_ready()) { if (!timer_pending(&stack.timer)) mod_timer(&stack.timer, jiffies + 1); - mix_pool_bytes(&stack.now, sizeof(stack.now)); + mix_pool_bytes(&stack.cycles, sizeof(stack.cycles)); schedule(); - stack.now = random_get_entropy(); + stack.cycles = random_get_entropy(); } del_timer_sync(&stack.timer); destroy_timer_on_stack(&stack.timer); - mix_pool_bytes(&stack.now, sizeof(stack.now)); + mix_pool_bytes(&stack.cycles, sizeof(stack.cycles)); } -- cgit v1.2.3 From c2a7de4feb6e09f23af7accc0f882a8fa92e7ae5 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sun, 13 Feb 2022 18:25:07 +0100 Subject: random: do crng pre-init loading in worker rather than irq Taking spinlocks from IRQ context is generally problematic for PREEMPT_RT. That is, in part, why we take trylocks instead. However, a spin_try_lock() is also problematic since another spin_lock() invocation can potentially PI-boost the wrong task, as the spin_try_lock() is invoked from an IRQ-context, so the task on CPU (random task or idle) is not the actual owner. Additionally, by deferring the crng pre-init loading to the worker, we can use the cryptographic hash function rather than xor, which is perhaps a meaningful difference when considering this data has only been through the relatively weak fast_mix() function. The biggest downside of this approach is that the pre-init loading is now deferred until later, which means things that need random numbers after interrupts are enabled, but before workqueues are running -- or before this particular worker manages to run -- are going to get into trouble. Hopefully in the real world, this window is rather small, especially since this code won't run until 64 interrupts had occurred. Cc: Sultan Alsawaf Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Eric Biggers Cc: Theodore Ts'o Acked-by: Sebastian Andrzej Siewior Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 65 +++++++++++++++------------------------------------ 1 file changed, 19 insertions(+), 46 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 3b83a6ac9f59..8171c3bbf460 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -443,10 +443,6 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], * boot time when it's better to have something there rather than * nothing. * - * There are two paths, a slow one and a fast one. The slow one - * hashes the input along with the current key. The fast one simply - * xors it in, and should only be used from interrupt context. - * * If account is set, then the crng_init_cnt counter is incremented. * This shouldn't be set by functions like add_device_randomness(), * where we can't trust the buffer passed to it is guaranteed to be @@ -455,19 +451,15 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], * Returns the number of bytes processed from input, which is bounded * by CRNG_INIT_CNT_THRESH if account is true. */ -static size_t crng_pre_init_inject(const void *input, size_t len, - bool fast, bool account) +static size_t crng_pre_init_inject(const void *input, size_t len, bool account) { static int crng_init_cnt = 0; + struct blake2s_state hash; unsigned long flags; - if (fast) { - if (!spin_trylock_irqsave(&base_crng.lock, flags)) - return 0; - } else { - spin_lock_irqsave(&base_crng.lock, flags); - } + blake2s_init(&hash, sizeof(base_crng.key)); + spin_lock_irqsave(&base_crng.lock, flags); if (crng_init != 0) { spin_unlock_irqrestore(&base_crng.lock, flags); return 0; @@ -476,21 +468,9 @@ static size_t crng_pre_init_inject(const void *input, size_t len, if (account) len = min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt); - if (fast) { - const u8 *src = input; - size_t i; - - for (i = 0; i < len; ++i) - base_crng.key[(crng_init_cnt + i) % - sizeof(base_crng.key)] ^= src[i]; - } else { - struct blake2s_state hash; - - blake2s_init(&hash, sizeof(base_crng.key)); - blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); - blake2s_update(&hash, input, len); - blake2s_final(&hash, base_crng.key); - } + blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); + blake2s_update(&hash, input, len); + blake2s_final(&hash, base_crng.key); if (account) { crng_init_cnt += len; @@ -1034,7 +1014,7 @@ void add_device_randomness(const void *buf, size_t size) unsigned long flags, now = jiffies; if (crng_init == 0 && size) - crng_pre_init_inject(buf, size, false, false); + crng_pre_init_inject(buf, size, false); spin_lock_irqsave(&input_pool.lock, flags); _mix_pool_bytes(&cycles, sizeof(cycles)); @@ -1155,7 +1135,7 @@ void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy) { if (unlikely(crng_init == 0)) { - size_t ret = crng_pre_init_inject(buffer, count, false, true); + size_t ret = crng_pre_init_inject(buffer, count, true); mix_pool_bytes(buffer, ret); count -= ret; buffer += ret; @@ -1295,8 +1275,14 @@ static void mix_interrupt_randomness(struct work_struct *work) fast_pool->last = jiffies; local_irq_enable(); - mix_pool_bytes(pool, sizeof(pool)); - credit_entropy_bits(1); + if (unlikely(crng_init == 0)) { + crng_pre_init_inject(pool, sizeof(pool), true); + mix_pool_bytes(pool, sizeof(pool)); + } else { + mix_pool_bytes(pool, sizeof(pool)); + credit_entropy_bits(1); + } + memzero_explicit(pool, sizeof(pool)); } @@ -1329,24 +1315,11 @@ void add_interrupt_randomness(int irq) fast_mix(fast_pool->pool32); new_count = ++fast_pool->count; - if (unlikely(crng_init == 0)) { - if (new_count >= 64 && - crng_pre_init_inject(fast_pool->pool32, sizeof(fast_pool->pool32), - true, true) > 0) { - fast_pool->count = 0; - fast_pool->last = now; - if (spin_trylock(&input_pool.lock)) { - _mix_pool_bytes(&fast_pool->pool32, sizeof(fast_pool->pool32)); - spin_unlock(&input_pool.lock); - } - } - return; - } - if (new_count & MIX_INFLIGHT) return; - if (new_count < 64 && !time_after(now, fast_pool->last + HZ)) + if (new_count < 64 && (!time_after(now, fast_pool->last + HZ) || + unlikely(crng_init == 0))) return; if (unlikely(!fast_pool->mix.func)) -- cgit v1.2.3 From 6f98a4bfee72c22f50aedb39fb761567969865fe Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Mon, 7 Feb 2022 17:19:24 +0100 Subject: random: block in /dev/urandom This topic has come up countless times, and usually doesn't go anywhere. This time I thought I'd bring it up with a slightly narrower focus, updated for some developments over the last three years: we finally can make /dev/urandom always secure, in light of the fact that our RNG is now always seeded. Ever since Linus' 50ee7529ec45 ("random: try to actively add entropy rather than passively wait for it"), the RNG does a haveged-style jitter dance around the scheduler, in order to produce entropy (and credit it) for the case when we're stuck in wait_for_random_bytes(). How ever you feel about the Linus Jitter Dance is beside the point: it's been there for three years and usually gets the RNG initialized in a second or so. As a matter of fact, this is what happens currently when people use getrandom(). It's already there and working, and most people have been using it for years without realizing. So, given that the kernel has grown this mechanism for seeding itself from nothing, and that this procedure happens pretty fast, maybe there's no point any longer in having /dev/urandom give insecure bytes. In the past we didn't want the boot process to deadlock, which was understandable. But now, in the worst case, a second goes by, and the problem is resolved. It seems like maybe we're finally at a point when we can get rid of the infamous "urandom read hole". The one slight drawback is that the Linus Jitter Dance relies on random_ get_entropy() being implemented. The first lines of try_to_generate_ entropy() are: stack.now = random_get_entropy(); if (stack.now == random_get_entropy()) return; On most platforms, random_get_entropy() is simply aliased to get_cycles(). The number of machines without a cycle counter or some other implementation of random_get_entropy() in 2022, which can also run a mainline kernel, and at the same time have a both broken and out of date userspace that relies on /dev/urandom never blocking at boot is thought to be exceedingly low. And to be clear: those museum pieces without cycle counters will continue to run Linux just fine, and even /dev/urandom will be operable just like before; the RNG just needs to be seeded first through the usual means, which should already be the case now. On systems that really do want unseeded randomness, we already offer getrandom(GRND_INSECURE), which is in use by, e.g., systemd for seeding their hash tables at boot. Nothing in this commit would affect GRND_INSECURE, and it remains the means of getting those types of random numbers. This patch goes a long way toward eliminating a long overdue userspace crypto footgun. After several decades of endless user confusion, we will finally be able to say, "use any single one of our random interfaces and you'll be fine. They're all the same. It doesn't matter." And that, I think, is really something. Finally all of those blog posts and disagreeing forums and contradictory articles will all become correct about whatever they happened to recommend, and along with it, a whole class of vulnerabilities eliminated. With very minimal downside, we're finally in a position where we can make this change. Cc: Dinh Nguyen Cc: Nick Hu Cc: Max Filippov Cc: Palmer Dabbelt Cc: David S. Miller Cc: Yoshinori Sato Cc: Michal Simek Cc: Borislav Petkov Cc: Guo Ren Cc: Geert Uytterhoeven Cc: Joshua Kinard Cc: David Laight Cc: Dominik Brodowski Cc: Eric Biggers Cc: Ard Biesheuvel Cc: Arnd Bergmann Cc: Thomas Gleixner Cc: Andy Lutomirski Cc: Kees Cook Cc: Lennart Poettering Cc: Konstantin Ryabitsev Cc: Linus Torvalds Cc: Greg Kroah-Hartman Cc: Theodore Ts'o Signed-off-by: Jason A. Donenfeld --- drivers/char/mem.c | 2 +- drivers/char/random.c | 72 ++++++++++++-------------------------------------- include/linux/random.h | 2 +- 3 files changed, 19 insertions(+), 57 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index cc296f0823bd..9f586025dbe6 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -707,7 +707,7 @@ static const struct memdev { [5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT }, [7] = { "full", 0666, &full_fops, 0 }, [8] = { "random", 0666, &random_fops, 0 }, - [9] = { "urandom", 0666, &urandom_fops, 0 }, + [9] = { "urandom", 0666, &random_fops, 0 }, #ifdef CONFIG_PRINTK [11] = { "kmsg", 0644, &kmsg_fops, 0 }, #endif diff --git a/drivers/char/random.c b/drivers/char/random.c index 8171c3bbf460..9831797e0699 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -89,17 +89,14 @@ static LIST_HEAD(random_ready_list); /* Control how we warn userspace. */ static struct ratelimit_state unseeded_warning = RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3); -static struct ratelimit_state urandom_warning = - RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3); static int ratelimit_disable __read_mostly; module_param_named(ratelimit_disable, ratelimit_disable, int, 0644); MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression"); /* * Returns whether or not the input pool has been seeded and thus guaranteed - * to supply cryptographically secure random numbers. This applies to: the - * /dev/urandom device, the get_random_bytes function, and the get_random_{u32, - * ,u64,int,long} family of functions. + * to supply cryptographically secure random numbers. This applies to + * get_random_bytes() and get_random_{u32,u64,int,long}(). * * Returns: true if the input pool has been seeded. * false if the input pool has not been seeded. @@ -115,10 +112,10 @@ static void try_to_generate_entropy(void); /* * Wait for the input pool to be seeded and thus guaranteed to supply - * cryptographically secure random numbers. This applies to: the /dev/urandom - * device, the get_random_bytes function, and the get_random_{u32,u64,int,long} - * family of functions. Using any of these functions without first calling - * this function forfeits the guarantee of security. + * cryptographically secure random numbers. This applies to + * get_random_bytes() and get_random_{u32,u64,int,long}(). Using any + * of these functions without first calling this function means that + * the returned numbers might not be cryptographically secure. * * Returns: 0 if the input pool has been seeded. * -ERESTARTSYS if the function was interrupted by a signal. @@ -256,10 +253,10 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller, void * unsigned long get_random_long() * * These interfaces will return the requested number of random bytes - * into the given buffer or as a return value. This is equivalent to - * a read from /dev/urandom. The integer family of functions may be - * higher performance for one-off random integers, because they do a - * bit of buffering. + * into the given buffer or as a return value. The returned numbers are + * the same as those of getrandom(0). The integer family of functions may + * be higher performance for one-off random integers, because they do a + * bit of buffering and do not invoke reseeding. * *********************************************************************/ @@ -336,11 +333,6 @@ static void crng_reseed(void) unseeded_warning.missed); unseeded_warning.missed = 0; } - if (urandom_warning.missed) { - pr_notice("%d urandom warning(s) missed due to ratelimiting\n", - urandom_warning.missed); - urandom_warning.missed = 0; - } } } @@ -993,10 +985,8 @@ int __init rand_initialize(void) pr_notice("crng init done (trusting CPU's manufacturer)\n"); } - if (ratelimit_disable) { - urandom_warning.interval = 0; + if (ratelimit_disable) unseeded_warning.interval = 0; - } return 0; } @@ -1386,20 +1376,16 @@ static void try_to_generate_entropy(void) * getrandom(2) is the primary modern interface into the RNG and should * be used in preference to anything else. * - * Reading from /dev/random has the same functionality as calling - * getrandom(2) with flags=0. In earlier versions, however, it had - * vastly different semantics and should therefore be avoided, to - * prevent backwards compatibility issues. - * - * Reading from /dev/urandom has the same functionality as calling - * getrandom(2) with flags=GRND_INSECURE. Because it does not block - * waiting for the RNG to be ready, it should not be used. + * Reading from /dev/random and /dev/urandom both have the same effect + * as calling getrandom(2) with flags=0. (In earlier versions, however, + * they each had different semantics.) * * Writing to either /dev/random or /dev/urandom adds entropy to * the input pool but does not credit it. * - * Polling on /dev/random indicates when the RNG is initialized, on - * the read side, and when it wants new entropy, on the write side. + * Polling on /dev/random or /dev/urandom indicates when the RNG + * is initialized, on the read side, and when it wants new entropy, + * on the write side. * * Both /dev/random and /dev/urandom have the same set of ioctls for * adding entropy, getting the entropy count, zeroing the count, and @@ -1484,21 +1470,6 @@ static ssize_t random_write(struct file *file, const char __user *buffer, return (ssize_t)count; } -static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes, - loff_t *ppos) -{ - static int maxwarn = 10; - - if (!crng_ready() && maxwarn > 0) { - maxwarn--; - if (__ratelimit(&urandom_warning)) - pr_notice("%s: uninitialized urandom read (%zd bytes read)\n", - current->comm, nbytes); - } - - return get_random_bytes_user(buf, nbytes); -} - static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { @@ -1585,15 +1556,6 @@ const struct file_operations random_fops = { .llseek = noop_llseek, }; -const struct file_operations urandom_fops = { - .read = urandom_read, - .write = random_write, - .unlocked_ioctl = random_ioctl, - .compat_ioctl = compat_ptr_ioctl, - .fasync = random_fasync, - .llseek = noop_llseek, -}; - /******************************************************************** * diff --git a/include/linux/random.h b/include/linux/random.h index 6148b8d1ccf3..725a4d08c0a0 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -44,7 +44,7 @@ extern void del_random_ready_callback(struct random_ready_callback *rdy); extern size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes); #ifndef MODULE -extern const struct file_operations random_fops, urandom_fops; +extern const struct file_operations random_fops; #endif u32 get_random_u32(void); -- cgit v1.2.3 From d0efdf35a6a71d307a250199af6fce122a7c7e11 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Mon, 28 Feb 2022 13:57:57 +0100 Subject: random: give sysctl_random_min_urandom_seed a more sensible value This isn't used by anything or anywhere, but we can't delete it due to compatibility. So at least give it the correct value of what it's supposed to be instead of a garbage one. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 9831797e0699..612e45e88077 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1581,7 +1581,7 @@ const struct file_operations random_fops = { * to avoid breaking old userspaces, but writing to it does not * change any behavior of the RNG. * - * - urandom_min_reseed_secs - fixed to the meaningless value "60". + * - urandom_min_reseed_secs - fixed to the value CRNG_RESEED_INTERVAL. * It is writable to avoid breaking old userspaces, but writing * to it does not change any behavior of the RNG. * @@ -1591,7 +1591,7 @@ const struct file_operations random_fops = { #include -static int sysctl_random_min_urandom_seed = 60; +static int sysctl_random_min_urandom_seed = CRNG_RESEED_INTERVAL / HZ; static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS; static int sysctl_poolsize = POOL_BITS; static u8 sysctl_bootid[UUID_SIZE]; -- cgit v1.2.3 From 77553cf8f44863b31da242cf24671d76ddb61597 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Mon, 28 Feb 2022 14:00:52 +0100 Subject: random: don't let 644 read-only sysctls be written to We leave around these old sysctls for compatibility, and we keep them "writable" for compatibility, but even after writing, we should keep reporting the same value. This is consistent with how userspaces tend to use sysctl_random_write_wakeup_bits, writing to it, and then later reading from it and using the value. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 612e45e88077..ede97649c5dd 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1631,6 +1631,13 @@ static int proc_do_uuid(struct ctl_table *table, int write, void *buffer, return proc_dostring(&fake_table, 0, buffer, lenp, ppos); } +/* The same as proc_dointvec, but writes don't change anything. */ +static int proc_do_rointvec(struct ctl_table *table, int write, void *buffer, + size_t *lenp, loff_t *ppos) +{ + return write ? 0 : proc_dointvec(table, 0, buffer, lenp, ppos); +} + static struct ctl_table random_table[] = { { .procname = "poolsize", @@ -1651,14 +1658,14 @@ static struct ctl_table random_table[] = { .data = &sysctl_random_write_wakeup_bits, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec, + .proc_handler = proc_do_rointvec, }, { .procname = "urandom_min_reseed_secs", .data = &sysctl_random_min_urandom_seed, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec, + .proc_handler = proc_do_rointvec, }, { .procname = "boot_id", -- cgit v1.2.3 From ae099e8e98fb01395228628be5a4661e3bd86fe4 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 23 Feb 2022 13:43:44 +0100 Subject: random: add mechanism for VM forks to reinitialize crng When a VM forks, we must immediately mix in additional information to the stream of random output so that two forks or a rollback don't produce the same stream of random numbers, which could have catastrophic cryptographic consequences. This commit adds a simple API, add_vmfork_ randomness(), for that, by force reseeding the crng. This has the added benefit of also draining the entropy pool and setting its timer back, so that any old entropy that was there prior -- which could have already been used by a different fork, or generally gone stale -- does not contribute to the accounting of the next 256 bits. Cc: Dominik Brodowski Cc: Theodore Ts'o Cc: Jann Horn Cc: Eric Biggers Reviewed-by: Ard Biesheuvel Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 50 +++++++++++++++++++++++++++++++++++--------------- include/linux/random.h | 1 + 2 files changed, 36 insertions(+), 15 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index ede97649c5dd..2b323f6bd96c 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -286,14 +286,14 @@ static DEFINE_PER_CPU(struct crng, crngs) = { }; /* Used by crng_reseed() to extract a new seed from the input pool. */ -static bool drain_entropy(void *buf, size_t nbytes); +static bool drain_entropy(void *buf, size_t nbytes, bool force); /* * This extracts a new crng key from the input pool, but only if there is a - * sufficient amount of entropy available, in order to mitigate bruteforcing - * of newly added bits. + * sufficient amount of entropy available or force is true, in order to + * mitigate bruteforcing of newly added bits. */ -static void crng_reseed(void) +static void crng_reseed(bool force) { unsigned long flags; unsigned long next_gen; @@ -301,7 +301,7 @@ static void crng_reseed(void) bool finalize_init = false; /* Only reseed if we can, to prevent brute forcing a small amount of new bits. */ - if (!drain_entropy(key, sizeof(key))) + if (!drain_entropy(key, sizeof(key), force)) return; /* @@ -398,7 +398,7 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], * in turn bumps the generation counter that we check below. */ if (unlikely(time_after(jiffies, READ_ONCE(base_crng.birth) + CRNG_RESEED_INTERVAL))) - crng_reseed(); + crng_reseed(false); local_lock_irqsave(&crngs.lock, flags); crng = raw_cpu_ptr(&crngs); @@ -763,10 +763,10 @@ EXPORT_SYMBOL(get_random_bytes_arch); * * Finally, extract entropy via these two, with the latter one * setting the entropy count to zero and extracting only if there - * is POOL_MIN_BITS entropy credited prior: + * is POOL_MIN_BITS entropy credited prior or force is true: * * static void extract_entropy(void *buf, size_t nbytes) - * static bool drain_entropy(void *buf, size_t nbytes) + * static bool drain_entropy(void *buf, size_t nbytes, bool force) * **********************************************************************/ @@ -824,7 +824,7 @@ static void credit_entropy_bits(size_t nbits) } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) - crng_reseed(); + crng_reseed(false); } /* @@ -874,16 +874,16 @@ static void extract_entropy(void *buf, size_t nbytes) } /* - * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we - * set the entropy count to zero (but don't actually touch any data). Only then - * can we extract a new key with extract_entropy(). + * First we make sure we have POOL_MIN_BITS of entropy in the pool unless force + * is true, and then we set the entropy count to zero (but don't actually touch + * any data). Only then can we extract a new key with extract_entropy(). */ -static bool drain_entropy(void *buf, size_t nbytes) +static bool drain_entropy(void *buf, size_t nbytes, bool force) { unsigned int entropy_count; do { entropy_count = READ_ONCE(input_pool.entropy_count); - if (entropy_count < POOL_MIN_BITS) + if (!force && entropy_count < POOL_MIN_BITS) return false; } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); extract_entropy(buf, nbytes); @@ -907,6 +907,7 @@ static bool drain_entropy(void *buf, size_t nbytes) * void add_hwgenerator_randomness(const void *buffer, size_t count, * size_t entropy); * void add_bootloader_randomness(const void *buf, size_t size); + * void add_vmfork_randomness(const void *unique_vm_id, size_t size); * void add_interrupt_randomness(int irq); * * add_device_randomness() adds data to the input pool that @@ -938,6 +939,10 @@ static bool drain_entropy(void *buf, size_t nbytes) * add_device_randomness(), depending on whether or not the configuration * option CONFIG_RANDOM_TRUST_BOOTLOADER is set. * + * add_vmfork_randomness() adds a unique (but not necessarily secret) ID + * representing the current instance of a VM to the pool, without crediting, + * and then force-reseeds the crng so that it takes effect immediately. + * * add_interrupt_randomness() uses the interrupt timing as random * inputs to the entropy pool. Using the cycle counters and the irq source * as inputs, it feeds the input pool roughly once a second or after 64 @@ -1163,6 +1168,21 @@ void add_bootloader_randomness(const void *buf, size_t size) } EXPORT_SYMBOL_GPL(add_bootloader_randomness); +/* + * Handle a new unique VM ID, which is unique, not secret, so we + * don't credit it, but we do immediately force a reseed after so + * that it's used by the crng posthaste. + */ +void add_vmfork_randomness(const void *unique_vm_id, size_t size) +{ + add_device_randomness(unique_vm_id, size); + if (crng_ready()) { + crng_reseed(true); + pr_notice("crng reseeded due to virtual machine fork\n"); + } +} +EXPORT_SYMBOL_GPL(add_vmfork_randomness); + struct fast_pool { union { u32 pool32[4]; @@ -1534,7 +1554,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) return -EPERM; if (crng_init < 2) return -ENODATA; - crng_reseed(); + crng_reseed(false); return 0; default: return -EINVAL; diff --git a/include/linux/random.h b/include/linux/random.h index 725a4d08c0a0..117468f3a92e 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -34,6 +34,7 @@ extern void add_input_randomness(unsigned int type, unsigned int code, extern void add_interrupt_randomness(int irq) __latent_entropy; extern void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy); +extern void add_vmfork_randomness(const void *unique_vm_id, size_t size); extern void get_random_bytes(void *buf, size_t nbytes); extern int wait_for_random_bytes(void); -- cgit v1.2.3 From d273845ecb0e0626842782a4497f0c5876139ec3 Mon Sep 17 00:00:00 2001 From: Alexander Graf Date: Fri, 25 Feb 2022 16:55:52 +0100 Subject: ACPI: allow longer device IDs We create a list of ACPI "PNP" IDs which contains _HID, _CID, and CLS entries of the respective devices. However, when making structs for matching, we squeeze those IDs into acpi_device_id, which only has 9 bytes space to store the identifier. The subsystem actually captures the full length of the IDs, and the modalias has the full length, but this struct we use for matching is limited. It originally had 16 bytes, but was changed to only have 9 in 6543becf26ff ("mod/file2alias: make modalias generation safe for cross compiling"), presumably on the theory that it would match the ACPI spec so it didn't matter. Unfortunately, while most people adhere to the ACPI specs, Microsoft decided that its VM Generation Counter device [1] should only be identifiable by _CID with a value of "VM_Gen_Counter", which is longer than 9 characters. To allow device drivers to match identifiers that exceed the 9 byte limit, this simply ups the length to 16, just like it was before the aforementioned commit. Empirical testing indicates that this doesn't actually increase vmlinux size on 64-bit, because the ulong in the same struct caused there to be 7 bytes of padding anyway, and when doing a s/M/Y/g i386_defconfig build, the bzImage only increased by 0.0055%, so negligible. This patch is a prerequisite to add support for VMGenID in Linux, the subsequent patch in this series. It has been confirmed to also work on the udev/modalias side in userspace. [1] https://download.microsoft.com/download/3/1/C/31CFC307-98CA-4CA5-914C-D9772691E214/VirtualMachineGenerationID.docx Signed-off-by: Alexander Graf Co-developed-by: Jason A. Donenfeld [Jason: reworked commit message a bit, went with len=16 approach.] Cc: Mika Westerberg Cc: Andy Shevchenko Cc: Len Brown Cc: Greg Kroah-Hartman Reviewed-by: Ard Biesheuvel Acked-by: Hans de Goede Acked-by: Rafael J. Wysocki Signed-off-by: Jason A. Donenfeld --- include/linux/mod_devicetable.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h index 4bb71979a8fd..5da5d990ff58 100644 --- a/include/linux/mod_devicetable.h +++ b/include/linux/mod_devicetable.h @@ -211,7 +211,7 @@ struct css_device_id { kernel_ulong_t driver_data; }; -#define ACPI_ID_LEN 9 +#define ACPI_ID_LEN 16 struct acpi_device_id { __u8 id[ACPI_ID_LEN]; -- cgit v1.2.3 From af6b54e2b5baa54c844573b6d49cc91157bcdd7e Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 23 Feb 2022 13:46:24 +0100 Subject: virt: vmgenid: notify RNG of VM fork and supply generation ID MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit VM Generation ID is a feature from Microsoft, described at , and supported by Hyper-V and QEMU. Its usage is described in Microsoft's RNG whitepaper, , as: If the OS is running in a VM, there is a problem that most hypervisors can snapshot the state of the machine and later rewind the VM state to the saved state. This results in the machine running a second time with the exact same RNG state, which leads to serious security problems. To reduce the window of vulnerability, Windows 10 on a Hyper-V VM will detect when the VM state is reset, retrieve a unique (not random) value from the hypervisor, and reseed the root RNG with that unique value. This does not eliminate the vulnerability, but it greatly reduces the time during which the RNG system will produce the same outputs as it did during a previous instantiation of the same VM state. Linux has the same issue, and given that vmgenid is supported already by multiple hypervisors, we can implement more or less the same solution. So this commit wires up the vmgenid ACPI notification to the RNG's newly added add_vmfork_randomness() function. It can be used from qemu via the `-device vmgenid,guid=auto` parameter. After setting that, use `savevm` in the monitor to save the VM state, then quit QEMU, start it again, and use `loadvm`. That will trigger this driver's notify function, which hands the new UUID to the RNG. This is described in . And there are hooks for this in libvirt as well, described in . Note, however, that the treatment of this as a UUID is considered to be an accidental QEMU nuance, per , so this driver simply treats these bytes as an opaque 128-bit binary blob, as per the spec. This doesn't really make a difference anyway, considering that's how it ends up when handed to the RNG in the end. Cc: Alexander Graf Cc: Adrian Catangiu Cc: Daniel P. BerrangĂ© Cc: Dominik Brodowski Cc: Wei Yongjun Tested-by: Souradeep Chakrabarti # With Hyper-V's virtual hardware Reviewed-by: Ard Biesheuvel Reviewed-by: Greg Kroah-Hartman Reviewed-by: Laszlo Ersek Signed-off-by: Jason A. Donenfeld --- MAINTAINERS | 1 + drivers/virt/Kconfig | 11 ++++++ drivers/virt/Makefile | 1 + drivers/virt/vmgenid.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 113 insertions(+) create mode 100644 drivers/virt/vmgenid.c diff --git a/MAINTAINERS b/MAINTAINERS index 777cd6fa2b3d..a10997e15146 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -16211,6 +16211,7 @@ M: Jason A. Donenfeld T: git https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git S: Maintained F: drivers/char/random.c +F: drivers/virt/vmgenid.c RAPIDIO SUBSYSTEM M: Matt Porter diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig index 8061e8ef449f..121b9293c737 100644 --- a/drivers/virt/Kconfig +++ b/drivers/virt/Kconfig @@ -13,6 +13,17 @@ menuconfig VIRT_DRIVERS if VIRT_DRIVERS +config VMGENID + tristate "Virtual Machine Generation ID driver" + default y + depends on ACPI + help + Say Y here to use the hypervisor-provided Virtual Machine Generation ID + to reseed the RNG when the VM is cloned. This is highly recommended if + you intend to do any rollback / cloning / snapshotting of VMs. + + Prefer Y to M so that this protection is activated very early. + config FSL_HV_MANAGER tristate "Freescale hypervisor management driver" depends on FSL_SOC diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile index 3e272ea60cd9..108d0ffcc9aa 100644 --- a/drivers/virt/Makefile +++ b/drivers/virt/Makefile @@ -4,6 +4,7 @@ # obj-$(CONFIG_FSL_HV_MANAGER) += fsl_hypervisor.o +obj-$(CONFIG_VMGENID) += vmgenid.o obj-y += vboxguest/ obj-$(CONFIG_NITRO_ENCLAVES) += nitro_enclaves/ diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c new file mode 100644 index 000000000000..0ae1a39f2e28 --- /dev/null +++ b/drivers/virt/vmgenid.c @@ -0,0 +1,100 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2022 Jason A. Donenfeld . All Rights Reserved. + * + * The "Virtual Machine Generation ID" is exposed via ACPI and changes when a + * virtual machine forks or is cloned. This driver exists for shepherding that + * information to random.c. + */ + +#include +#include +#include +#include + +ACPI_MODULE_NAME("vmgenid"); + +enum { VMGENID_SIZE = 16 }; + +struct vmgenid_state { + u8 *next_id; + u8 this_id[VMGENID_SIZE]; +}; + +static int vmgenid_add(struct acpi_device *device) +{ + struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER }; + struct vmgenid_state *state; + union acpi_object *obj; + phys_addr_t phys_addr; + acpi_status status; + int ret = 0; + + state = devm_kmalloc(&device->dev, sizeof(*state), GFP_KERNEL); + if (!state) + return -ENOMEM; + + status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed); + if (ACPI_FAILURE(status)) { + ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR")); + return -ENODEV; + } + obj = parsed.pointer; + if (!obj || obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 2 || + obj->package.elements[0].type != ACPI_TYPE_INTEGER || + obj->package.elements[1].type != ACPI_TYPE_INTEGER) { + ret = -EINVAL; + goto out; + } + + phys_addr = (obj->package.elements[0].integer.value << 0) | + (obj->package.elements[1].integer.value << 32); + state->next_id = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB); + if (IS_ERR(state->next_id)) { + ret = PTR_ERR(state->next_id); + goto out; + } + + memcpy(state->this_id, state->next_id, sizeof(state->this_id)); + add_device_randomness(state->this_id, sizeof(state->this_id)); + + device->driver_data = state; + +out: + ACPI_FREE(parsed.pointer); + return ret; +} + +static void vmgenid_notify(struct acpi_device *device, u32 event) +{ + struct vmgenid_state *state = acpi_driver_data(device); + u8 old_id[VMGENID_SIZE]; + + memcpy(old_id, state->this_id, sizeof(old_id)); + memcpy(state->this_id, state->next_id, sizeof(state->this_id)); + if (!memcmp(old_id, state->this_id, sizeof(old_id))) + return; + add_vmfork_randomness(state->this_id, sizeof(state->this_id)); +} + +static const struct acpi_device_id vmgenid_ids[] = { + { "VM_GEN_COUNTER", 0 }, + { } +}; + +static struct acpi_driver vmgenid_driver = { + .name = "vmgenid", + .ids = vmgenid_ids, + .owner = THIS_MODULE, + .ops = { + .add = vmgenid_add, + .notify = vmgenid_notify + } +}; + +module_acpi_driver(vmgenid_driver); + +MODULE_DEVICE_TABLE(acpi, vmgenid_ids); +MODULE_DESCRIPTION("Virtual Machine Generation ID"); +MODULE_LICENSE("GPL v2"); +MODULE_AUTHOR("Jason A. Donenfeld "); -- cgit v1.2.3 From a4107d34f960df99ca07fa8eb022425a804f59f3 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 1 Mar 2022 15:14:04 +0100 Subject: random: do not export add_vmfork_randomness() unless needed Since add_vmfork_randomness() is only called from vmgenid.o, we can guard it in CONFIG_VMGENID, similarly to how we do with add_disk_randomness() and CONFIG_BLOCK. If we ever have multiple things calling into add_vmfork_randomness(), we can add another shared Kconfig symbol for that, but for now, this is good enough. Even though add_vmfork_randomess() is a pretty small function, removing it means that there are only calls to crng_reseed(false) and none to crng_reseed(true), which means the compiler can constant propagate the false, removing branches from crng_reseed() and its descendants. Additionally, we don't even need the symbol to be exported if CONFIG_VMGENID is not a module, so conditionalize that too. Cc: Dominik Brodowski Cc: Theodore Ts'o Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 4 ++++ include/linux/random.h | 2 ++ 2 files changed, 6 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index 2b323f6bd96c..bc2a4f7e3655 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1168,6 +1168,7 @@ void add_bootloader_randomness(const void *buf, size_t size) } EXPORT_SYMBOL_GPL(add_bootloader_randomness); +#if IS_ENABLED(CONFIG_VMGENID) /* * Handle a new unique VM ID, which is unique, not secret, so we * don't credit it, but we do immediately force a reseed after so @@ -1181,7 +1182,10 @@ void add_vmfork_randomness(const void *unique_vm_id, size_t size) pr_notice("crng reseeded due to virtual machine fork\n"); } } +#if IS_MODULE(CONFIG_VMGENID) EXPORT_SYMBOL_GPL(add_vmfork_randomness); +#endif +#endif struct fast_pool { union { diff --git a/include/linux/random.h b/include/linux/random.h index 117468f3a92e..f209f1a78899 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -34,7 +34,9 @@ extern void add_input_randomness(unsigned int type, unsigned int code, extern void add_interrupt_randomness(int irq) __latent_entropy; extern void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy); +#if IS_ENABLED(CONFIG_VMGENID) extern void add_vmfork_randomness(const void *unique_vm_id, size_t size); +#endif extern void get_random_bytes(void *buf, size_t nbytes); extern int wait_for_random_bytes(void); -- cgit v1.2.3 From 5acd35487dc911541672b3ffc322851769c32a56 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 1 Mar 2022 20:03:49 +0100 Subject: random: replace custom notifier chain with standard one We previously rolled our own randomness readiness notifier, which only has two users in the whole kernel. Replace this with a more standard atomic notifier block that serves the same purpose with less code. Also unexport the symbols, because no modules use it, only unconditional builtins. The only drawback is that it's possible for a notification handler returning the "stop" code to prevent further processing, but given that there are only two users, and that we're unexporting this anyway, that doesn't seem like a significant drawback for the simplification we receive here. Cc: Greg Kroah-Hartman Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 67 ++++++++++++++------------------------------------ include/linux/random.h | 10 +++----- lib/random32.c | 12 +++++---- lib/vsprintf.c | 10 +++++--- 4 files changed, 35 insertions(+), 64 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index bc2a4f7e3655..aa7bc9a3a864 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -83,8 +83,8 @@ static int crng_init = 0; /* Various types of waiters for crng_init->2 transition. */ static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); static struct fasync_struct *fasync; -static DEFINE_SPINLOCK(random_ready_list_lock); -static LIST_HEAD(random_ready_list); +static DEFINE_SPINLOCK(random_ready_chain_lock); +static RAW_NOTIFIER_HEAD(random_ready_chain); /* Control how we warn userspace. */ static struct ratelimit_state unseeded_warning = @@ -144,72 +144,43 @@ EXPORT_SYMBOL(wait_for_random_bytes); * * returns: 0 if callback is successfully added * -EALREADY if pool is already initialised (callback not called) - * -ENOENT if module for callback is not alive */ -int add_random_ready_callback(struct random_ready_callback *rdy) +int register_random_ready_notifier(struct notifier_block *nb) { - struct module *owner; unsigned long flags; - int err = -EALREADY; + int ret = -EALREADY; if (crng_ready()) - return err; - - owner = rdy->owner; - if (!try_module_get(owner)) - return -ENOENT; - - spin_lock_irqsave(&random_ready_list_lock, flags); - if (crng_ready()) - goto out; - - owner = NULL; - - list_add(&rdy->list, &random_ready_list); - err = 0; - -out: - spin_unlock_irqrestore(&random_ready_list_lock, flags); - - module_put(owner); + return ret; - return err; + spin_lock_irqsave(&random_ready_chain_lock, flags); + if (!crng_ready()) + ret = raw_notifier_chain_register(&random_ready_chain, nb); + spin_unlock_irqrestore(&random_ready_chain_lock, flags); + return ret; } -EXPORT_SYMBOL(add_random_ready_callback); /* * Delete a previously registered readiness callback function. */ -void del_random_ready_callback(struct random_ready_callback *rdy) +int unregister_random_ready_notifier(struct notifier_block *nb) { unsigned long flags; - struct module *owner = NULL; - - spin_lock_irqsave(&random_ready_list_lock, flags); - if (!list_empty(&rdy->list)) { - list_del_init(&rdy->list); - owner = rdy->owner; - } - spin_unlock_irqrestore(&random_ready_list_lock, flags); + int ret; - module_put(owner); + spin_lock_irqsave(&random_ready_chain_lock, flags); + ret = raw_notifier_chain_unregister(&random_ready_chain, nb); + spin_unlock_irqrestore(&random_ready_chain_lock, flags); + return ret; } -EXPORT_SYMBOL(del_random_ready_callback); static void process_random_ready_list(void) { unsigned long flags; - struct random_ready_callback *rdy, *tmp; - spin_lock_irqsave(&random_ready_list_lock, flags); - list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) { - struct module *owner = rdy->owner; - - list_del_init(&rdy->list); - rdy->func(rdy); - module_put(owner); - } - spin_unlock_irqrestore(&random_ready_list_lock, flags); + spin_lock_irqsave(&random_ready_chain_lock, flags); + raw_notifier_call_chain(&random_ready_chain, 0, NULL); + spin_unlock_irqrestore(&random_ready_chain_lock, flags); } #define warn_unseeded_randomness(previous) \ diff --git a/include/linux/random.h b/include/linux/random.h index f209f1a78899..fab1ab0563b4 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -10,11 +10,7 @@ #include -struct random_ready_callback { - struct list_head list; - void (*func)(struct random_ready_callback *rdy); - struct module *owner; -}; +struct notifier_block; extern void add_device_randomness(const void *, size_t); extern void add_bootloader_randomness(const void *, size_t); @@ -42,8 +38,8 @@ extern void get_random_bytes(void *buf, size_t nbytes); extern int wait_for_random_bytes(void); extern int __init rand_initialize(void); extern bool rng_is_initialized(void); -extern int add_random_ready_callback(struct random_ready_callback *rdy); -extern void del_random_ready_callback(struct random_ready_callback *rdy); +extern int register_random_ready_notifier(struct notifier_block *nb); +extern int unregister_random_ready_notifier(struct notifier_block *nb); extern size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes); #ifndef MODULE diff --git a/lib/random32.c b/lib/random32.c index 3c19820796d0..976632003ec6 100644 --- a/lib/random32.c +++ b/lib/random32.c @@ -551,9 +551,11 @@ static void prandom_reseed(struct timer_list *unused) * To avoid worrying about whether it's safe to delay that interrupt * long enough to seed all CPUs, just schedule an immediate timer event. */ -static void prandom_timer_start(struct random_ready_callback *unused) +static int prandom_timer_start(struct notifier_block *nb, + unsigned long action, void *data) { mod_timer(&seed_timer, jiffies); + return 0; } #ifdef CONFIG_RANDOM32_SELFTEST @@ -617,13 +619,13 @@ core_initcall(prandom32_state_selftest); */ static int __init prandom_init_late(void) { - static struct random_ready_callback random_ready = { - .func = prandom_timer_start + static struct notifier_block random_ready = { + .notifier_call = prandom_timer_start }; - int ret = add_random_ready_callback(&random_ready); + int ret = register_random_ready_notifier(&random_ready); if (ret == -EALREADY) { - prandom_timer_start(&random_ready); + prandom_timer_start(&random_ready, 0, NULL); ret = 0; } return ret; diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 3b8129dd374c..36574a806a81 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -757,14 +757,16 @@ static void enable_ptr_key_workfn(struct work_struct *work) static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn); -static void fill_random_ptr_key(struct random_ready_callback *unused) +static int fill_random_ptr_key(struct notifier_block *nb, + unsigned long action, void *data) { /* This may be in an interrupt handler. */ queue_work(system_unbound_wq, &enable_ptr_key_work); + return 0; } -static struct random_ready_callback random_ready = { - .func = fill_random_ptr_key +static struct notifier_block random_ready = { + .notifier_call = fill_random_ptr_key }; static int __init initialize_ptr_random(void) @@ -778,7 +780,7 @@ static int __init initialize_ptr_random(void) return 0; } - ret = add_random_ready_callback(&random_ready); + ret = register_random_ready_notifier(&random_ready); if (!ret) { return 0; } else if (ret == -EALREADY) { -- cgit v1.2.3 From f3c2682bad7bc6033c837e9c66e5af881fe8d465 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 1 Mar 2022 20:22:39 +0100 Subject: random: provide notifier for VM fork Drivers such as WireGuard need to learn when VMs fork in order to clear sessions. This commit provides a simple notifier_block for that, with a register and unregister function. When no VM fork detection is compiled in, this turns into a no-op, similar to how the power notifier works. Cc: Dominik Brodowski Cc: Theodore Ts'o Reviewed-by: Greg Kroah-Hartman Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 15 +++++++++++++++ include/linux/random.h | 5 +++++ 2 files changed, 20 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index aa7bc9a3a864..d9ca441c14bd 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1140,6 +1140,8 @@ void add_bootloader_randomness(const void *buf, size_t size) EXPORT_SYMBOL_GPL(add_bootloader_randomness); #if IS_ENABLED(CONFIG_VMGENID) +static BLOCKING_NOTIFIER_HEAD(vmfork_chain); + /* * Handle a new unique VM ID, which is unique, not secret, so we * don't credit it, but we do immediately force a reseed after so @@ -1152,10 +1154,23 @@ void add_vmfork_randomness(const void *unique_vm_id, size_t size) crng_reseed(true); pr_notice("crng reseeded due to virtual machine fork\n"); } + blocking_notifier_call_chain(&vmfork_chain, 0, NULL); } #if IS_MODULE(CONFIG_VMGENID) EXPORT_SYMBOL_GPL(add_vmfork_randomness); #endif + +int register_random_vmfork_notifier(struct notifier_block *nb) +{ + return blocking_notifier_chain_register(&vmfork_chain, nb); +} +EXPORT_SYMBOL_GPL(register_random_vmfork_notifier); + +int unregister_random_vmfork_notifier(struct notifier_block *nb) +{ + return blocking_notifier_chain_unregister(&vmfork_chain, nb); +} +EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier); #endif struct fast_pool { diff --git a/include/linux/random.h b/include/linux/random.h index fab1ab0563b4..c0baffe7afb1 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -32,6 +32,11 @@ extern void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy); #if IS_ENABLED(CONFIG_VMGENID) extern void add_vmfork_randomness(const void *unique_vm_id, size_t size); +extern int register_random_vmfork_notifier(struct notifier_block *nb); +extern int unregister_random_vmfork_notifier(struct notifier_block *nb); +#else +static inline int register_random_vmfork_notifier(struct notifier_block *nb) { return 0; } +static inline int unregister_random_vmfork_notifier(struct notifier_block *nb) { return 0; } #endif extern void get_random_bytes(void *buf, size_t nbytes); -- cgit v1.2.3 From 2d6919c3205b141ba85fb733b2a67937ff85dc7f Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 1 Mar 2022 23:26:55 +0100 Subject: wireguard: device: clear keys on VM fork When a virtual machine forks, it's important that WireGuard clear existing sessions so that different plaintexts are not transmitted using the same key+nonce, which can result in catastrophic cryptographic failure. To accomplish this, we simply hook into the newly added vmfork notifier. As a bonus, it turns out that, like the vmfork registration function, the PM registration function is stubbed out when CONFIG_PM_SLEEP is not set, so we can actually just remove the maze of ifdefs, which makes it really quite clean to support both notifiers at once. Cc: Dominik Brodowski Cc: Greg Kroah-Hartman Cc: Theodore Ts'o Acked-by: Jakub Kicinski Signed-off-by: Jason A. Donenfeld --- drivers/net/wireguard/device.c | 38 +++++++++++++++++++++++++++----------- 1 file changed, 27 insertions(+), 11 deletions(-) diff --git a/drivers/net/wireguard/device.c b/drivers/net/wireguard/device.c index a46067c38bf5..0fad1331303c 100644 --- a/drivers/net/wireguard/device.c +++ b/drivers/net/wireguard/device.c @@ -59,9 +59,7 @@ out: return ret; } -#ifdef CONFIG_PM_SLEEP -static int wg_pm_notification(struct notifier_block *nb, unsigned long action, - void *data) +static int wg_pm_notification(struct notifier_block *nb, unsigned long action, void *data) { struct wg_device *wg; struct wg_peer *peer; @@ -92,7 +90,24 @@ static int wg_pm_notification(struct notifier_block *nb, unsigned long action, } static struct notifier_block pm_notifier = { .notifier_call = wg_pm_notification }; -#endif + +static int wg_vm_notification(struct notifier_block *nb, unsigned long action, void *data) +{ + struct wg_device *wg; + struct wg_peer *peer; + + rtnl_lock(); + list_for_each_entry(wg, &device_list, device_list) { + mutex_lock(&wg->device_update_lock); + list_for_each_entry(peer, &wg->peer_list, peer_list) + wg_noise_expire_current_peer_keypairs(peer); + mutex_unlock(&wg->device_update_lock); + } + rtnl_unlock(); + return 0; +} + +static struct notifier_block vm_notifier = { .notifier_call = wg_vm_notification }; static int wg_stop(struct net_device *dev) { @@ -424,16 +439,18 @@ int __init wg_device_init(void) { int ret; -#ifdef CONFIG_PM_SLEEP ret = register_pm_notifier(&pm_notifier); if (ret) return ret; -#endif - ret = register_pernet_device(&pernet_ops); + ret = register_random_vmfork_notifier(&vm_notifier); if (ret) goto error_pm; + ret = register_pernet_device(&pernet_ops); + if (ret) + goto error_vm; + ret = rtnl_link_register(&link_ops); if (ret) goto error_pernet; @@ -442,10 +459,10 @@ int __init wg_device_init(void) error_pernet: unregister_pernet_device(&pernet_ops); +error_vm: + unregister_random_vmfork_notifier(&vm_notifier); error_pm: -#ifdef CONFIG_PM_SLEEP unregister_pm_notifier(&pm_notifier); -#endif return ret; } @@ -453,8 +470,7 @@ void wg_device_uninit(void) { rtnl_link_unregister(&link_ops); unregister_pernet_device(&pernet_ops); -#ifdef CONFIG_PM_SLEEP + unregister_random_vmfork_notifier(&vm_notifier); unregister_pm_notifier(&pm_notifier); -#endif rcu_barrier(); } -- cgit v1.2.3 From f5eab0e2db4f881fb2b62b3fdad5b9be673dd7ae Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 11 Feb 2022 14:58:44 +0100 Subject: random: use SipHash as interrupt entropy accumulator The current fast_mix() function is a piece of classic mailing list crypto, where it just sort of sprung up by an anonymous author without a lot of real analysis of what precisely it was accomplishing. As an ARX permutation alone, there are some easily searchable differential trails in it, and as a means of preventing malicious interrupts, it completely fails, since it xors new data into the entire state every time. It can't really be analyzed as a random permutation, because it clearly isn't, and it can't be analyzed as an interesting linear algebraic structure either, because it's also not that. There really is very little one can say about it in terms of entropy accumulation. It might diffuse bits, some of the time, maybe, we hope, I guess. But for the most part, it fails to accomplish anything concrete. As a reminder, the simple goal of add_interrupt_randomness() is to simply accumulate entropy until ~64 interrupts have elapsed, and then dump it into the main input pool, which uses a cryptographic hash. It would be nice to have something cryptographically strong in the interrupt handler itself, in case a malicious interrupt compromises a per-cpu fast pool within the 64 interrupts / 1 second window, and then inside of that same window somehow can control its return address and cycle counter, even if that's a bit far fetched. However, with a very CPU-limited budget, actually doing that remains an active research project (and perhaps there'll be something useful for Linux to come out of it). And while the abundance of caution would be nice, this isn't *currently* the security model, and we don't yet have a fast enough solution to make it our security model. Plus there's not exactly a pressing need to do that. (And for the avoidance of doubt, the actual cluster of 64 accumulated interrupts still gets dumped into our cryptographically secure input pool.) So, for now we are going to stick with the existing interrupt security model, which assumes that each cluster of 64 interrupt data samples is mostly non-malicious and not colluding with an infoleaker. With this as our goal, we have a few more choices, simply aiming to accumulate entropy, while discarding the least amount of it. We know from that random oracles, instantiated as computational hash functions, make good entropy accumulators and extractors, which is the justification for using BLAKE2s in the main input pool. As mentioned, we don't have that luxury here, but we also don't have the same security model requirements, because we're assuming that there aren't malicious inputs. A pseudorandom function instance can approximately behave like a random oracle, provided that the key is uniformly random. But since we're not concerned with malicious inputs, we can pick a fixed key, which is not secret, knowing that "nature" won't interact with a sufficiently chosen fixed key by accident. So we pick a PRF with a fixed initial key, and accumulate into it continuously, dumping the result every 64 interrupts into our cryptographically secure input pool. For this, we make use of SipHash-1-x on 64-bit and HalfSipHash-1-x on 32-bit, which are already in use in the kernel's hsiphash family of functions and achieve the same performance as the function they replace. It would be nice to do two rounds, but we don't exactly have the CPU budget handy for that, and one round alone is already sufficient. As mentioned, we start with a fixed initial key (zeros is fine), and allow SipHash's symmetry breaking constants to turn that into a useful starting point. Also, since we're dumping the result (or half of it on 64-bit so as to tax our hash function the same amount on all platforms) into the cryptographically secure input pool, there's no point in finalizing SipHash's output, since it'll wind up being finalized by something much stronger. This means that all we need to do is use the ordinary round function word-by-word, as normal SipHash does. Simplified, the flow is as follows: Initialize: siphash_state_t state; siphash_init(&state, key={0, 0, 0, 0}); Update (accumulate) on interrupt: siphash_update(&state, interrupt_data_and_timing); Dump into input pool after 64 interrupts: blake2s_update(&input_pool, &state, sizeof(state) / 2); The result of all of this is that the security model is unchanged from before -- we assume non-malicious inputs -- yet we now implement that model with a stronger argument. I would like to emphasize, again, that the purpose of this commit is to improve the existing design, by making it analyzable, without changing any fundamental assumptions. There may well be value down the road in changing up the existing design, using something cryptographically strong, or simply using a ring buffer of samples rather than having a fast_mix() at all, or changing which and how much data we collect each interrupt so that we can use something linear, or a variety of other ideas. This commit does not invalidate the potential for those in the future. For example, in the future, if we're able to characterize the data we're collecting on each interrupt, we may be able to inch toward information theoretic accumulators. shows that `s = ror32(s, 7) ^ x` and `s = ror64(s, 19) ^ x` make very good accumulators for 2-monotone distributions, which would apply to timestamp counters, like random_get_entropy() or jiffies, but would not apply to our current combination of the two values, or to the various function addresses and register values we mix in. Alternatively, shows that max-period linear functions with no non-trivial invariant subspace make good extractors, used in the form `s = f(s) ^ x`. However, this only works if the input data is both identical and independent, and obviously a collection of address values and counters fails; so it goes with theoretical papers. Future directions here may involve trying to characterize more precisely what we actually need to collect in the interrupt handler, and building something specific around that. However, as mentioned, the morass of data we're gathering at the interrupt handler presently defies characterization, and so we use SipHash for now, which works well and performs well. Cc: Theodore Ts'o Cc: Greg Kroah-Hartman Reviewed-by: Jean-Philippe Aumasson Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 94 ++++++++++++++++++++++++++++++--------------------- 1 file changed, 55 insertions(+), 39 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index d9ca441c14bd..50973a074d2d 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1174,48 +1174,51 @@ EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier); #endif struct fast_pool { - union { - u32 pool32[4]; - u64 pool64[2]; - }; struct work_struct mix; + unsigned long pool[4]; unsigned long last; unsigned int count; u16 reg_idx; }; +static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = { +#ifdef CONFIG_64BIT + /* SipHash constants */ + .pool = { 0x736f6d6570736575UL, 0x646f72616e646f6dUL, + 0x6c7967656e657261UL, 0x7465646279746573UL } +#else + /* HalfSipHash constants */ + .pool = { 0, 0, 0x6c796765U, 0x74656462U } +#endif +}; + /* - * This is a fast mixing routine used by the interrupt randomness - * collector. It's hardcoded for an 128 bit pool and assumes that any - * locks that might be needed are taken by the caller. + * This is [Half]SipHash-1-x, starting from an empty key. Because + * the key is fixed, it assumes that its inputs are non-malicious, + * and therefore this has no security on its own. s represents the + * 128 or 256-bit SipHash state, while v represents a 128-bit input. */ -static void fast_mix(u32 pool[4]) +static void fast_mix(unsigned long s[4], const unsigned long *v) { - u32 a = pool[0], b = pool[1]; - u32 c = pool[2], d = pool[3]; - - a += b; c += d; - b = rol32(b, 6); d = rol32(d, 27); - d ^= a; b ^= c; - - a += b; c += d; - b = rol32(b, 16); d = rol32(d, 14); - d ^= a; b ^= c; - - a += b; c += d; - b = rol32(b, 6); d = rol32(d, 27); - d ^= a; b ^= c; - - a += b; c += d; - b = rol32(b, 16); d = rol32(d, 14); - d ^= a; b ^= c; + size_t i; - pool[0] = a; pool[1] = b; - pool[2] = c; pool[3] = d; + for (i = 0; i < 16 / sizeof(long); ++i) { + s[3] ^= v[i]; +#ifdef CONFIG_64BIT + s[0] += s[1]; s[1] = rol64(s[1], 13); s[1] ^= s[0]; s[0] = rol64(s[0], 32); + s[2] += s[3]; s[3] = rol64(s[3], 16); s[3] ^= s[2]; + s[0] += s[3]; s[3] = rol64(s[3], 21); s[3] ^= s[0]; + s[2] += s[1]; s[1] = rol64(s[1], 17); s[1] ^= s[2]; s[2] = rol64(s[2], 32); +#else + s[0] += s[1]; s[1] = rol32(s[1], 5); s[1] ^= s[0]; s[0] = rol32(s[0], 16); + s[2] += s[3]; s[3] = rol32(s[3], 8); s[3] ^= s[2]; + s[0] += s[3]; s[3] = rol32(s[3], 7); s[3] ^= s[0]; + s[2] += s[1]; s[1] = rol32(s[1], 13); s[1] ^= s[2]; s[2] = rol32(s[2], 16); +#endif + s[0] ^= v[i]; + } } -static DEFINE_PER_CPU(struct fast_pool, irq_randomness); - #ifdef CONFIG_SMP /* * This function is called when the CPU has just come online, with @@ -1257,7 +1260,15 @@ static unsigned long get_reg(struct fast_pool *f, struct pt_regs *regs) static void mix_interrupt_randomness(struct work_struct *work) { struct fast_pool *fast_pool = container_of(work, struct fast_pool, mix); - u32 pool[4]; + /* + * The size of the copied stack pool is explicitly 16 bytes so that we + * tax mix_pool_byte()'s compression function the same amount on all + * platforms. This means on 64-bit we copy half the pool into this, + * while on 32-bit we copy all of it. The entropy is supposed to be + * sufficiently dispersed between bits that in the sponge-like + * half case, on average we don't wind up "losing" some. + */ + u8 pool[16]; /* Check to see if we're running on the wrong CPU due to hotplug. */ local_irq_disable(); @@ -1270,7 +1281,7 @@ static void mix_interrupt_randomness(struct work_struct *work) * Copy the pool to the stack so that the mixer always has a * consistent view, before we reenable irqs again. */ - memcpy(pool, fast_pool->pool32, sizeof(pool)); + memcpy(pool, fast_pool->pool, sizeof(pool)); fast_pool->count = 0; fast_pool->last = jiffies; local_irq_enable(); @@ -1294,25 +1305,30 @@ void add_interrupt_randomness(int irq) struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness); struct pt_regs *regs = get_irq_regs(); unsigned int new_count; + union { + u32 u32[4]; + u64 u64[2]; + unsigned long longs[16 / sizeof(long)]; + } irq_data; if (cycles == 0) cycles = get_reg(fast_pool, regs); if (sizeof(cycles) == 8) - fast_pool->pool64[0] ^= cycles ^ rol64(now, 32) ^ irq; + irq_data.u64[0] = cycles ^ rol64(now, 32) ^ irq; else { - fast_pool->pool32[0] ^= cycles ^ irq; - fast_pool->pool32[1] ^= now; + irq_data.u32[0] = cycles ^ irq; + irq_data.u32[1] = now; } if (sizeof(unsigned long) == 8) - fast_pool->pool64[1] ^= regs ? instruction_pointer(regs) : _RET_IP_; + irq_data.u64[1] = regs ? instruction_pointer(regs) : _RET_IP_; else { - fast_pool->pool32[2] ^= regs ? instruction_pointer(regs) : _RET_IP_; - fast_pool->pool32[3] ^= get_reg(fast_pool, regs); + irq_data.u32[2] = regs ? instruction_pointer(regs) : _RET_IP_; + irq_data.u32[3] = get_reg(fast_pool, regs); } - fast_mix(fast_pool->pool32); + fast_mix(fast_pool->pool, irq_data.longs); new_count = ++fast_pool->count; if (new_count & MIX_INFLIGHT) -- cgit v1.2.3 From a96cfe2d427064325ecbf56df8816c6b871ec285 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Mar 2022 11:20:17 -0700 Subject: random: make consistent usage of crng_ready() Rather than sometimes checking `crng_init < 2`, we should always use the crng_ready() macro, so that should we change anything later, it's consistent. Additionally, that macro already has a likely() around it, which means we don't need to open code our own likely() and unlikely() annotations. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 50973a074d2d..19a602c69f2f 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -122,18 +122,13 @@ static void try_to_generate_entropy(void); */ int wait_for_random_bytes(void) { - if (likely(crng_ready())) - return 0; - - do { + while (!crng_ready()) { int ret; ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ); if (ret) return ret > 0 ? 0 : ret; - try_to_generate_entropy(); - } while (!crng_ready()); - + } return 0; } EXPORT_SYMBOL(wait_for_random_bytes); @@ -288,7 +283,7 @@ static void crng_reseed(bool force) ++next_gen; WRITE_ONCE(base_crng.generation, next_gen); WRITE_ONCE(base_crng.birth, jiffies); - if (crng_init < 2) { + if (!crng_ready()) { crng_init = 2; finalize_init = true; } @@ -351,7 +346,7 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], * ready, we do fast key erasure with the base_crng directly, because * this is what crng_pre_init_inject() mutates during early init. */ - if (unlikely(!crng_ready())) { + if (!crng_ready()) { bool ready; spin_lock_irqsave(&base_crng.lock, flags); @@ -794,7 +789,7 @@ static void credit_entropy_bits(size_t nbits) entropy_count = min_t(unsigned int, POOL_BITS, orig + add); } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig); - if (crng_init < 2 && entropy_count >= POOL_MIN_BITS) + if (!crng_ready() && entropy_count >= POOL_MIN_BITS) crng_reseed(false); } @@ -956,7 +951,7 @@ int __init rand_initialize(void) extract_entropy(base_crng.key, sizeof(base_crng.key)); ++base_crng.generation; - if (arch_init && trust_cpu && crng_init < 2) { + if (arch_init && trust_cpu && !crng_ready()) { crng_init = 2; pr_notice("crng init done (trusting CPU's manufacturer)\n"); } @@ -1558,7 +1553,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) case RNDRESEEDCRNG: if (!capable(CAP_SYS_ADMIN)) return -EPERM; - if (crng_init < 2) + if (!crng_ready()) return -ENODATA; crng_reseed(false); return 0; -- cgit v1.2.3 From 7a7ff644aeaf071d433caffb3b8ea57354b55bd3 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Mar 2022 23:32:34 -0700 Subject: random: reseed more often immediately after booting In order to chip away at the "premature first" problem, we augment our existing entropy accounting with more frequent reseedings at boot. The idea is that at boot, we're getting entropy from various places, and we're not very sure which of early boot entropy is good and which isn't. Even when we're crediting the entropy, we're still not totally certain that it's any good. Since boot is the one time (aside from a compromise) that we have zero entropy, it's important that we shepherd entropy into the crng fairly often. At the same time, we don't want a "premature next" problem, whereby an attacker can brute force individual bits of added entropy. In lieu of going full-on Fortuna (for now), we can pick a simpler strategy of just reseeding more often during the first 5 minutes after boot. This is still bounded by the 256-bit entropy credit requirement, so we'll skip a reseeding if we haven't reached that, but in case entropy /is/ coming in, this ensures that it makes its way into the crng rather rapidly during these early stages. Ordinarily we reseed if the previous reseeding is 300 seconds old. This commit changes things so that for the first 600 seconds of boot time, we reseed if the previous reseeding is uptime / 2 seconds old. That means that we'll reseed at the very least double the uptime of the previous reseeding. Cc: Theodore Ts'o Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 19a602c69f2f..defdba110d1d 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -327,6 +327,28 @@ static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE], memzero_explicit(first_block, sizeof(first_block)); } +/* + * Return whether the crng seed is considered to be sufficiently + * old that a reseeding might be attempted. This happens if the last + * reseeding was CRNG_RESEED_INTERVAL ago, or during early boot, at + * an interval proportional to the uptime. + */ +static bool crng_has_old_seed(void) +{ + static bool early_boot = true; + unsigned long interval = CRNG_RESEED_INTERVAL; + + if (unlikely(READ_ONCE(early_boot))) { + time64_t uptime = ktime_get_seconds(); + if (uptime >= CRNG_RESEED_INTERVAL / HZ * 2) + WRITE_ONCE(early_boot, false); + else + interval = max_t(unsigned int, 5 * HZ, + (unsigned int)uptime / 2 * HZ); + } + return time_after(jiffies, READ_ONCE(base_crng.birth) + interval); +} + /* * This function returns a ChaCha state that you may use for generating * random data. It also returns up to 32 bytes on its own of random data @@ -360,10 +382,10 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS], } /* - * If the base_crng is more than 5 minutes old, we reseed, which - * in turn bumps the generation counter that we check below. + * If the base_crng is old enough, we try to reseed, which in turn + * bumps the generation counter that we check below. */ - if (unlikely(time_after(jiffies, READ_ONCE(base_crng.birth) + CRNG_RESEED_INTERVAL))) + if (unlikely(crng_has_old_seed())) crng_reseed(false); local_lock_irqsave(&crngs.lock, flags); -- cgit v1.2.3 From 3e504d2026eb6c8762cd6040ae57db166516824a Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 8 Mar 2022 10:12:16 -0700 Subject: random: check for signal and try earlier when generating entropy Rather than waiting a full second in an interruptable waiter before trying to generate entropy, try to generate entropy first and wait second. While waiting one second might give an extra second for getting entropy from elsewhere, we're already pretty late in the init process here, and whatever else is generating entropy will still continue to contribute. This has implications on signal handling: we call try_to_generate_entropy() from wait_for_random_bytes(), and wait_for_random_bytes() always uses wait_event_interruptible_timeout() when waiting, since it's called by userspace code in restartable contexts, where signals can pend. Since try_to_generate_entropy() now runs first, if a signal is pending, it's necessary for try_to_generate_entropy() to check for signals, since it won't hit the wait until after try_to_generate_entropy() has returned. And even before this change, when entering a busy loop in try_to_generate_entropy(), we should have been checking to see if any signals are pending, so that a process doesn't get stuck in that loop longer than expected. Cc: Theodore Ts'o Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index defdba110d1d..0bdefada7453 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -124,10 +124,11 @@ int wait_for_random_bytes(void) { while (!crng_ready()) { int ret; + + try_to_generate_entropy(); ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ); if (ret) return ret > 0 ? 0 : ret; - try_to_generate_entropy(); } return 0; } @@ -1398,7 +1399,7 @@ static void try_to_generate_entropy(void) return; timer_setup_on_stack(&stack.timer, entropy_timer, 0); - while (!crng_ready()) { + while (!crng_ready() && !signal_pending(current)) { if (!timer_pending(&stack.timer)) mod_timer(&stack.timer, jiffies + 1); mix_pool_bytes(&stack.cycles, sizeof(stack.cycles)); -- cgit v1.2.3