/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_KCSAN_CHECKS_H
#define _LINUX_KCSAN_CHECKS_H
#include <linux/types.h>
/*
* ACCESS TYPE MODIFIERS
*
* <none>: normal read access;
* WRITE : write access;
* ATOMIC: access is atomic;
* ASSERT: access is not a regular access, but an assertion;
*/
#define KCSAN_ACCESS_WRITE 0x1
#define KCSAN_ACCESS_ATOMIC 0x2
#define KCSAN_ACCESS_ASSERT 0x4
/*
* __kcsan_*: Always calls into the runtime when KCSAN is enabled. This may be used
* even in compilation units that selectively disable KCSAN, but must use KCSAN
* to validate access to an address. Never use these in header files!
*/
#ifdef CONFIG_KCSAN
/**
* __kcsan_check_access - check generic access for races
*
* @ptr: address of access
* @size: size of access
* @type: access type modifier
*/
void __kcsan_check_access(const volatile void *ptr, size_t size, int type);
/**
* kcsan_nestable_atomic_begin - begin nestable atomic region
*
* Accesses within the atomic region may appear to race with other accesses but
* should be considered atomic.
*/
void kcsan_nestable_atomic_begin(void);
/**
* kcsan_nestable_atomic_end - end nestable atomic region
*/
void kcsan_nestable_atomic_end(void);
/**
* kcsan_flat_atomic_begin - begin flat atomic region
*
* Accesses within the atomic region may appear to race with other accesses but
* should be considered atomic.
*/
void kcsan_flat_atomic_begin(void);
/**
* kcsan_flat_atomic_end - end flat atomic region
*/
void kcsan_flat_atomic_end(void);
/**
* kcsan_atomic_next - consider following accesses as atomic
*
* Force treating the next n memory accesses for the current context as atomic
* operations.
*
* @n: number of following memory accesses to treat as atomic.
*/
void kcsan_atomic_next(int n);
/**
* kcsan_set_access_mask - set access mask
*
* Set the access mask for all accesses for the current context if non-zero.
* Only value changes to bits set in the mask will be reported.
*
* @mask: bitmask
*/
void kcsan_set_access_mask(unsigned long mask);
#else /* CONFIG_KCSAN */
static inline void __kcsan_check_access(const volatile void *ptr, size_t size,
int type) { }
static inline void kcsan_nestable_atomic_begin(void) { }
static inline void kcsan_nestable_atomic_end(void) { }
static inline void kcsan_flat_atomic_begin(void) { }
static inline void kcsan_flat_atomic_end(void) { }
static inline void kcsan_atomic_next(int n) { }
static inline void kcsan_set_access_mask(unsigned long mask) { }
#endif /* CONFIG_KCSAN */
/*
* kcsan_*: Only calls into the runtime when the particular compilation unit has
* KCSAN instrumentation enabled. May be used in header files.
*/
#ifdef __SANITIZE_THREAD__
#define kcsan_check_access __kcsan_check_access
#else
static inline void kcsan_check_access(const volatile void *ptr, size_t size,
int type) { }
#endif
/**
* __kcsan_check_read - check regular read access for races
*
* @ptr: address of access
* @size: size of access
*/
#define __kcsan_check_read(ptr, size) __kcsan_check_access(ptr, size, 0)
/**
* __kcsan_check_write - check regular write access for races
*
* @ptr: address of access
* @size: size of access
*/
#define __kcsan_check_write(ptr, size) \
__kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
/**
* kcsan_check_read - check regular read access for races
*
* @ptr: address of access
* @size: size of access
*/
#define kcsan_check_read(ptr, size) kcsan_check_access(ptr, size, 0)
/**
* kcsan_check_write - check regular write access for races
*
* @ptr: address of access
* @size: size of access
*/
#define kcsan_check_write(ptr, size) \
kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
/*
* Check for atomic accesses: if atomic accesses are not ignored, this simply
* aliases to kcsan_check_access(), otherwise becomes a no-op.
*/
#ifdef CONFIG_KCSAN_IGNORE_ATOMICS
#define kcsan_check_atomic_read(...) do { } while (0)
#define kcsan_check_atomic_write(...) do { } while (0)
#else
#define kcsan_check_atomic_read(ptr, size) \
kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC)
#define kcsan_check_atomic_write(ptr, size) \
kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE)
#endif
/**
* ASSERT_EXCLUSIVE_WRITER - assert no concurrent writes to @var
*
* Assert that there are no concurrent writes to @var; other readers are
* allowed. This assertion can be used to specify properties of concurrent code,
* where violation cannot be detected as a normal data race.
*
* For example, if we only have a single writer, but multiple concurrent
* readers, to avoid data races, all these accesses must be marked; even
* concurrent marked writes racing with the single writer are bugs.
* Unfortunately, due to being marked, they are no longer data races. For cases
* like these, we can use the macro as follows:
*
* .. code-block:: c
*
* void writer(void) {
* spin_lock(&update_foo_lock);
* ASSERT_EXCLUSIVE_WRITER(shared_foo);
* WRITE_ONCE(shared_foo, ...);
* spin_unlock(&update_foo_lock);
* }
* void reader(void) {
* // update_foo_lock does not need to be held!
* ... = READ_ONCE(shared_foo);
* }
*
* @var: variable to assert on
*/
#define ASSERT_EXCLUSIVE_WRITER(var) \
__kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_ASSERT)
/**
* ASSERT_EXCLUSIVE_ACCESS - assert no concurrent accesses to @var
*
* Assert that there are no concurrent accesses to @var (no readers nor
* writers). This assertion can be used to specify properties of concurrent
* code, where violation cannot be detected as a normal data race.
*
* For example, where exclusive access is expected after determining no other
* users of an object are left, but the object is not actually freed. We can
* check that this property actually holds as follows:
*
* .. code-block:: c
*
* if (refcount_dec_and_test(&obj->refcnt)) {
* ASSERT_EXCLUSIVE_ACCESS(*obj);
* do_some_cleanup(obj);
* release_for_reuse(obj);
* }
*
* Note: For cases where the object is freed, `KASAN <kasan.html>`_ is a better
* fit to detect use-after-free bugs.
*
* @var: variable to assert on
*/
#define ASSERT_EXCLUSIVE_ACCESS(var) \
__kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT)
/**
* ASSERT_EXCLUSIVE_BITS - assert no concurrent writes to subset of bits in @var
*
* Bit-granular variant of ASSERT_EXCLUSIVE_WRITER(var).
*
* Assert that there are no concurrent writes to a subset of bits in @var;
* concurrent readers are permitted. This assertion captures more detailed
* bit-level properties, compared to the other (word granularity) assertions.
* Only the bits set in @mask are checked for concurrent modifications, while
* ignoring the remaining bits, i.e. concurrent writes (or reads) to ~mask bits
* are ignored.
*
* Use this for variables, where some bits must not be modified concurrently,
* yet other bits are expected to be modified concurrently.
*
* For example, variables where, after initialization, some bits are read-only,
* but other bits may still be modified concurrently. A reader may wish to
* assert that this is true as follows:
*
* .. code-block:: c
*
* ASSERT_EXCLUSIVE_BITS(flags, READ_ONLY_MASK);
* foo = (READ_ONCE(flags) & READ_ONLY_MASK) >> READ_ONLY_SHIFT;
*
* Note: The access that immediately follows ASSERT_EXCLUSIVE_BITS() is assumed
* to access the masked bits only, and KCSAN optimistically assumes it is
* therefore safe, even in the presence of data races, and marking it with
* READ_ONCE() is optional from KCSAN's point-of-view. We caution, however, that
* it may still be advisable to do so, since we cannot reason about all compiler
* optimizations when it comes to bit manipulations (on the reader and writer
* side). If you are sure nothing can go wrong, we can write the above simply
* as:
*
* .. code-block:: c
*
* ASSERT_EXCLUSIVE_BITS(flags, READ_ONLY_MASK);
* foo = (flags & READ_ONLY_MASK) >> READ_ONLY_SHIFT;
*
* Another example, where this may be used, is when certain bits of @var may
* only be modified when holding the appropriate lock, but other bits may still
* be modified concurrently. Writers, where other bits may change concurrently,
* could use the assertion as follows:
*
* .. code-block:: c
*
* spin_lock(&foo_lock);
* ASSERT_EXCLUSIVE_BITS(flags, FOO_MASK);
* old_flags = flags;
* new_flags = (old_flags & ~FOO_MASK) | (new_foo << FOO_SHIFT);
* if (cmpxchg(&flags, old_flags, new_flags) != old_flags) { ... }
* spin_unlock(&foo_lock);
*
* @var: variable to assert on
* @mask: only check for modifications to bits set in @mask
*/
#define ASSERT_EXCLUSIVE_BITS(var, mask) \
do { \
kcsan_set_access_mask(mask); \
__kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_ASSERT);\
kcsan_set_access_mask(0); \
kcsan_atomic_next(1); \
} while (0)
#endif /* _LINUX_KCSAN_CHECKS_H */
