From d6083f040d5d8f8d748462c77e90547097df936e Mon Sep 17 00:00:00 2001 From: Leon Hwang Date: Tue, 15 Oct 2024 23:02:06 +0800 Subject: bpf: Prevent tailcall infinite loop caused by freplace There is a potential infinite loop issue that can occur when using a combination of tail calls and freplace. In an upcoming selftest, the attach target for entry_freplace of tailcall_freplace.c is subprog_tc of tc_bpf2bpf.c, while the tail call in entry_freplace leads to entry_tc. This results in an infinite loop: entry_tc -> subprog_tc -> entry_freplace --tailcall-> entry_tc. The problem arises because the tail_call_cnt in entry_freplace resets to zero each time entry_freplace is executed, causing the tail call mechanism to never terminate, eventually leading to a kernel panic. To fix this issue, the solution is twofold: 1. Prevent updating a program extended by an freplace program to a prog_array map. 2. Prevent extending a program that is already part of a prog_array map with an freplace program. This ensures that: * If a program or its subprogram has been extended by an freplace program, it can no longer be updated to a prog_array map. * If a program has been added to a prog_array map, neither it nor its subprograms can be extended by an freplace program. Moreover, an extension program should not be tailcalled. As such, return -EINVAL if the program has a type of BPF_PROG_TYPE_EXT when adding it to a prog_array map. Additionally, fix a minor code style issue by replacing eight spaces with a tab for proper formatting. Reviewed-by: Eduard Zingerman Signed-off-by: Leon Hwang Link: https://lore.kernel.org/r/20241015150207.70264-2-leon.hwang@linux.dev Signed-off-by: Alexei Starovoitov --- kernel/bpf/core.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/bpf/core.c') diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 5e77c58e0601..233ea78f8f1b 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -131,6 +131,7 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag INIT_LIST_HEAD_RCU(&fp->aux->ksym_prefix.lnode); #endif mutex_init(&fp->aux->used_maps_mutex); + mutex_init(&fp->aux->ext_mutex); mutex_init(&fp->aux->dst_mutex); return fp; -- cgit v1.2.3 From a76ab5731e32d50ff5b1ae97e9dc4b23f41c23f5 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Tue, 12 Nov 2024 08:39:07 -0800 Subject: bpf: Find eligible subprogs for private stack support Private stack will be allocated with percpu allocator in jit time. To avoid complexity at runtime, only one copy of private stack is available per cpu per prog. So runtime recursion check is necessary to avoid stack corruption. Current private stack only supports kprobe/perf_event/tp/raw_tp which has recursion check in the kernel, and prog types that use bpf trampoline recursion check. For trampoline related prog types, currently only tracing progs have recursion checking. To avoid complexity, all async_cb subprogs use normal kernel stack including those subprogs used by both main prog subtree and async_cb subtree. Any prog having tail call also uses kernel stack. To avoid jit penalty with private stack support, a subprog stack size threshold is set such that only if the stack size is no less than the threshold, private stack is supported. The current threshold is 64 bytes. This avoids jit penality if the stack usage is small. A useless 'continue' is also removed from a loop in func check_max_stack_depth(). Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20241112163907.2223839-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov --- include/linux/bpf_verifier.h | 7 ++++ include/linux/filter.h | 1 + kernel/bpf/core.c | 5 +++ kernel/bpf/verifier.c | 96 +++++++++++++++++++++++++++++++++++++++----- 4 files changed, 99 insertions(+), 10 deletions(-) (limited to 'kernel/bpf/core.c') diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 3a74033d49c4..d62bb2ca1828 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -633,6 +633,12 @@ struct bpf_subprog_arg_info { }; }; +enum priv_stack_mode { + PRIV_STACK_UNKNOWN, + NO_PRIV_STACK, + PRIV_STACK_ADAPTIVE, +}; + struct bpf_subprog_info { /* 'start' has to be the first field otherwise find_subprog() won't work */ u32 start; /* insn idx of function entry point */ @@ -653,6 +659,7 @@ struct bpf_subprog_info { /* true if bpf_fastcall stack region is used by functions that can't be inlined */ bool keep_fastcall_stack: 1; + enum priv_stack_mode priv_stack_mode; u8 arg_cnt; struct bpf_subprog_arg_info args[MAX_BPF_FUNC_REG_ARGS]; }; diff --git a/include/linux/filter.h b/include/linux/filter.h index 7d7578a8eac1..3a21947f2fd4 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -1119,6 +1119,7 @@ bool bpf_jit_supports_exceptions(void); bool bpf_jit_supports_ptr_xchg(void); bool bpf_jit_supports_arena(void); bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena); +bool bpf_jit_supports_private_stack(void); u64 bpf_arch_uaddress_limit(void); void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie); bool bpf_helper_changes_pkt_data(void *func); diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 233ea78f8f1b..14d9288441f2 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -3045,6 +3045,11 @@ bool __weak bpf_jit_supports_exceptions(void) return false; } +bool __weak bpf_jit_supports_private_stack(void) +{ + return false; +} + void __weak arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie) { } diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9f5de8d4fbd0..fb23793ac53d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -194,6 +194,8 @@ struct bpf_verifier_stack_elem { #define BPF_GLOBAL_PERCPU_MA_MAX_SIZE 512 +#define BPF_PRIV_STACK_MIN_SIZE 64 + static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx); static int release_reference(struct bpf_verifier_env *env, int ref_obj_id); static void invalidate_non_owning_refs(struct bpf_verifier_env *env); @@ -6090,6 +6092,34 @@ static int check_ptr_alignment(struct bpf_verifier_env *env, strict); } +static enum priv_stack_mode bpf_enable_priv_stack(struct bpf_prog *prog) +{ + if (!bpf_jit_supports_private_stack()) + return NO_PRIV_STACK; + + /* bpf_prog_check_recur() checks all prog types that use bpf trampoline + * while kprobe/tp/perf_event/raw_tp don't use trampoline hence checked + * explicitly. + */ + switch (prog->type) { + case BPF_PROG_TYPE_KPROBE: + case BPF_PROG_TYPE_TRACEPOINT: + case BPF_PROG_TYPE_PERF_EVENT: + case BPF_PROG_TYPE_RAW_TRACEPOINT: + return PRIV_STACK_ADAPTIVE; + case BPF_PROG_TYPE_TRACING: + case BPF_PROG_TYPE_LSM: + case BPF_PROG_TYPE_STRUCT_OPS: + if (bpf_prog_check_recur(prog)) + return PRIV_STACK_ADAPTIVE; + fallthrough; + default: + break; + } + + return NO_PRIV_STACK; +} + static int round_up_stack_depth(struct bpf_verifier_env *env, int stack_depth) { if (env->prog->jit_requested) @@ -6107,17 +6137,20 @@ static int round_up_stack_depth(struct bpf_verifier_env *env, int stack_depth) * Since recursion is prevented by check_cfg() this algorithm * only needs a local stack of MAX_CALL_FRAMES to remember callsites */ -static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx) +static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx, + bool priv_stack_supported) { struct bpf_subprog_info *subprog = env->subprog_info; struct bpf_insn *insn = env->prog->insnsi; - int depth = 0, frame = 0, i, subprog_end; + int depth = 0, frame = 0, i, subprog_end, subprog_depth; bool tail_call_reachable = false; int ret_insn[MAX_CALL_FRAMES]; int ret_prog[MAX_CALL_FRAMES]; int j; i = subprog[idx].start; + if (!priv_stack_supported) + subprog[idx].priv_stack_mode = NO_PRIV_STACK; process_func: /* protect against potential stack overflow that might happen when * bpf2bpf calls get combined with tailcalls. Limit the caller's stack @@ -6144,11 +6177,31 @@ process_func: depth); return -EACCES; } - depth += round_up_stack_depth(env, subprog[idx].stack_depth); - if (depth > MAX_BPF_STACK) { - verbose(env, "combined stack size of %d calls is %d. Too large\n", - frame + 1, depth); - return -EACCES; + + subprog_depth = round_up_stack_depth(env, subprog[idx].stack_depth); + if (priv_stack_supported) { + /* Request private stack support only if the subprog stack + * depth is no less than BPF_PRIV_STACK_MIN_SIZE. This is to + * avoid jit penalty if the stack usage is small. + */ + if (subprog[idx].priv_stack_mode == PRIV_STACK_UNKNOWN && + subprog_depth >= BPF_PRIV_STACK_MIN_SIZE) + subprog[idx].priv_stack_mode = PRIV_STACK_ADAPTIVE; + } + + if (subprog[idx].priv_stack_mode == PRIV_STACK_ADAPTIVE) { + if (subprog_depth > MAX_BPF_STACK) { + verbose(env, "stack size of subprog %d is %d. Too large\n", + idx, subprog_depth); + return -EACCES; + } + } else { + depth += subprog_depth; + if (depth > MAX_BPF_STACK) { + verbose(env, "combined stack size of %d calls is %d. Too large\n", + frame + 1, depth); + return -EACCES; + } } continue_func: subprog_end = subprog[idx + 1].start; @@ -6205,6 +6258,8 @@ continue_func: } i = next_insn; idx = sidx; + if (!priv_stack_supported) + subprog[idx].priv_stack_mode = NO_PRIV_STACK; if (subprog[idx].has_tail_call) tail_call_reachable = true; @@ -6238,7 +6293,8 @@ continue_func: */ if (frame == 0) return 0; - depth -= round_up_stack_depth(env, subprog[idx].stack_depth); + if (subprog[idx].priv_stack_mode != PRIV_STACK_ADAPTIVE) + depth -= round_up_stack_depth(env, subprog[idx].stack_depth); frame--; i = ret_insn[frame]; idx = ret_prog[frame]; @@ -6247,16 +6303,36 @@ continue_func: static int check_max_stack_depth(struct bpf_verifier_env *env) { + enum priv_stack_mode priv_stack_mode = PRIV_STACK_UNKNOWN; struct bpf_subprog_info *si = env->subprog_info; + bool priv_stack_supported; int ret; for (int i = 0; i < env->subprog_cnt; i++) { + if (si[i].has_tail_call) { + priv_stack_mode = NO_PRIV_STACK; + break; + } + } + + if (priv_stack_mode == PRIV_STACK_UNKNOWN) + priv_stack_mode = bpf_enable_priv_stack(env->prog); + + /* All async_cb subprogs use normal kernel stack. If a particular + * subprog appears in both main prog and async_cb subtree, that + * subprog will use normal kernel stack to avoid potential nesting. + * The reverse subprog traversal ensures when main prog subtree is + * checked, the subprogs appearing in async_cb subtrees are already + * marked as using normal kernel stack, so stack size checking can + * be done properly. + */ + for (int i = env->subprog_cnt - 1; i >= 0; i--) { if (!i || si[i].is_async_cb) { - ret = check_max_stack_depth_subprog(env, i); + priv_stack_supported = !i && priv_stack_mode == PRIV_STACK_ADAPTIVE; + ret = check_max_stack_depth_subprog(env, i, priv_stack_supported); if (ret < 0) return ret; } - continue; } return 0; } -- cgit v1.2.3