Syzbot caught an array out-of-bounds bug [1]. It turns out that when the BPF program runs through do_misc_fixups(), it allocates an extra 8 bytes on the call stack, which eventually causes stack_depth to exceed 512.
I was able to reproduce this issue probabilistically by enabling CONFIG_UBSAN=y and disabling CONFIG_BPF_JIT_ALWAYS_ON with the selfttest I provide in second patch(although it doesn't happen every time - I didn't dig deeper into why UBSAN behaves this way).
Furthermore, if I set /proc/sys/net/core/bpf_jit_enable to 0 to disable the jit, a panic occurs, and the reason is the same, that bpf_func is assigned an incorrect address.
[---[ end trace ]--- [Oops: general protection fault, probably for non-canonical address 0x100f0e0e0d090808: 0000 [#1] PREEMPT SMP NOPTI [Tainted: [W]=WARN, [O]=OOT_MODULE [RIP: 0010:bpf_test_run+0x1d2/0x360 [RSP: 0018:ffffafc7955178a0 EFLAGS: 00010246 [RAX: 100f0e0e0d090808 RBX: ffff8e9fdb2c4100 RCX: 0000000000000018 [RDX: 00000000002b5b18 RSI: ffffafc780497048 RDI: ffff8ea04d601700 [RBP: ffffafc780497000 R08: ffffafc795517a0c R09: 0000000000000000 [R10: 0000000000000000 R11: fefefefefefefeff R12: ffff8ea04d601700 [R13: ffffafc795517928 R14: ffffafc795517928 R15: 0000000000000000 [CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [CR2: 00007f181c064648 CR3: 00000001aa2be003 CR4: 0000000000770ef0 [DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400 [PKRU: 55555554 [Call Trace: [ <TASK> [ ? die_addr+0x36/0x90 [ ? exc_general_protection+0x237/0x430 [ ? asm_exc_general_protection+0x26/0x30 [ ? bpf_test_run+0x1d2/0x360 [ ? bpf_test_run+0x10d/0x360 [ ? __link_object+0x12a/0x1e0 [ ? slab_build_skb+0x23/0x130 [ ? kmem_cache_alloc_noprof+0x2ea/0x3f0 [ ? sk_prot_alloc+0xc2/0x120 [ bpf_prog_test_run_skb+0x21b/0x590 [ __sys_bpf+0x340/0xa80 [ __x64_sys_bpf+0x1e/0x30
--- v2 -> v3: Optimized some code naming and conditional judgment logic. https://lore.kernel.org/bpf/20250213131214.164982-1-mrpre@163.com/T/
v1 -> v2: Directly reject loading programs with a stack size greater than 512 when jit disabled.(Suggested by Alexei Starovoitov) https://lore.kernel.org/bpf/20250212135251.85487-1-mrpre@163.com/T/
Jiayuan Chen (3): bpf: Fix array bounds error with may_goto selftests/bpf: Introduce __load_if_JITed annotation for tests selftests/bpf: Add selftest for may_goto
kernel/bpf/core.c | 19 +++++-- kernel/bpf/verifier.c | 7 +++ tools/testing/selftests/bpf/progs/bpf_misc.h | 2 + .../selftests/bpf/progs/verifier_stack_ptr.c | 52 +++++++++++++++++++ tools/testing/selftests/bpf/test_loader.c | 26 ++++++++++ 5 files changed, 102 insertions(+), 4 deletions(-)
may_goto uses an additional 8 bytes on the stack, which causes the interpreters[] array to go out of bounds when calculating index by stack_size.
1. If a BPF program is rewritten, re-evaluate the stack size. For non-JIT cases, reject loading directly.
2. For non-JIT cases, calculating interpreters[idx] may still cause out-of-bounds array access, and just warn about it.
3. For jit_requested cases, the execution of bpf_func also needs to be warned. So move the definition of function __bpf_prog_ret0_warn out of the macro definition CONFIG_BPF_JIT_ALWAYS_ON.
Reported-by: syzbot+d2a2c639d03ac200a4f1@syzkaller.appspotmail.com Closes: https://lore.kernel.org/bpf/0000000000000f823606139faa5d@google.com/ Fixes: 011832b97b311 ("bpf: Introduce may_goto instruction") Signed-off-by: Jiayuan Chen mrpre@163.com --- kernel/bpf/core.c | 19 +++++++++++++++---- kernel/bpf/verifier.c | 7 +++++++ 2 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index da729cbbaeb9..a0200fbbace9 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2290,17 +2290,18 @@ void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth) insn->code = BPF_JMP | BPF_CALL_ARGS; } #endif -#else +#endif + static unsigned int __bpf_prog_ret0_warn(const void *ctx, const struct bpf_insn *insn) { /* If this handler ever gets executed, then BPF_JIT_ALWAYS_ON - * is not working properly, so warn about it! + * is not working properly, or interpreter is being used when + * prog->jit_requested is not 0, so warn about it! */ WARN_ON_ONCE(1); return 0; } -#endif
bool bpf_prog_map_compatible(struct bpf_map *map, const struct bpf_prog *fp) @@ -2380,8 +2381,18 @@ static void bpf_prog_select_func(struct bpf_prog *fp) { #ifndef CONFIG_BPF_JIT_ALWAYS_ON u32 stack_depth = max_t(u32, fp->aux->stack_depth, 1); + u32 idx = (round_up(stack_depth, 32) / 32) - 1;
- fp->bpf_func = interpreters[(round_up(stack_depth, 32) / 32) - 1]; + /* may_goto may cause stack size > 512, leading to idx out-of-bounds. + * But for non-JITed programs, we don't need bpf_func, so no bounds + * check needed. + */ + if (!fp->jit_requested && + !WARN_ON_ONCE(idx >= ARRAY_SIZE(interpreters))) { + fp->bpf_func = interpreters[idx]; + } else { + fp->bpf_func = __bpf_prog_ret0_warn; + } #else fp->bpf_func = __bpf_prog_ret0_warn; #endif diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9971c03adfd5..fcd302904ba0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -21882,6 +21882,13 @@ static int do_misc_fixups(struct bpf_verifier_env *env) if (subprogs[cur_subprog + 1].start == i + delta + 1) { subprogs[cur_subprog].stack_depth += stack_depth_extra; subprogs[cur_subprog].stack_extra = stack_depth_extra; + + stack_depth = subprogs[cur_subprog].stack_depth; + if (stack_depth > MAX_BPF_STACK && !prog->jit_requested) { + verbose(env, "stack size %d(extra %d) is too large\n", + stack_depth, stack_depth_extra); + return -EINVAL; + } cur_subprog++; stack_depth = subprogs[cur_subprog].stack_depth; stack_depth_extra = 0;
In some cases, the verification logic under the interpreter and JIT differs, such as may_goto, and the test program behaves differently under different runtime modes, requiring separate verification logic for each result.
Introduce __load_if_JITed and __load_if_no_JITed annotation for tests.
Signed-off-by: Jiayuan Chen mrpre@163.com --- tools/testing/selftests/bpf/progs/bpf_misc.h | 2 ++ tools/testing/selftests/bpf/test_loader.c | 26 ++++++++++++++++++++ 2 files changed, 28 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h index f45f4352feeb..a40d5c0040ec 100644 --- a/tools/testing/selftests/bpf/progs/bpf_misc.h +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h @@ -135,6 +135,8 @@ #define __arch_arm64 __arch("ARM64") #define __arch_riscv64 __arch("RISCV64") #define __caps_unpriv(caps) __attribute__((btf_decl_tag("comment:test_caps_unpriv=" EXPAND_QUOTE(caps)))) +#define __load_if_JITed() __attribute__((btf_decl_tag("comment:load_mode=jited"))) +#define __load_if_no_JITed() __attribute__((btf_decl_tag("comment:load_mode=no_jited")))
/* Define common capabilities tested using __caps_unpriv */ #define CAP_NET_ADMIN 12 diff --git a/tools/testing/selftests/bpf/test_loader.c b/tools/testing/selftests/bpf/test_loader.c index 53b06647cf57..4d23a9c463ee 100644 --- a/tools/testing/selftests/bpf/test_loader.c +++ b/tools/testing/selftests/bpf/test_loader.c @@ -37,6 +37,7 @@ #define TEST_TAG_JITED_PFX "comment:test_jited=" #define TEST_TAG_JITED_PFX_UNPRIV "comment:test_jited_unpriv=" #define TEST_TAG_CAPS_UNPRIV "comment:test_caps_unpriv=" +#define TEST_TAG_LOAD_MODE_PFX "comment:load_mode="
/* Warning: duplicated in bpf_misc.h */ #define POINTER_VALUE 0xcafe4all @@ -55,6 +56,11 @@ enum mode { UNPRIV = 2 };
+enum load_mode { + JITED = 1 << 0, + NO_JITED = 1 << 1, +}; + struct expect_msg { const char *substr; /* substring match */ regex_t regex; @@ -87,6 +93,7 @@ struct test_spec { int prog_flags; int mode_mask; int arch_mask; + int load_mask; bool auxiliary; bool valid; }; @@ -406,6 +413,7 @@ static int parse_test_spec(struct test_loader *tester, bool collect_jit = false; int func_id, i, err = 0; u32 arch_mask = 0; + u32 load_mask = 0; struct btf *btf; enum arch arch;
@@ -580,10 +588,22 @@ static int parse_test_spec(struct test_loader *tester, if (err) goto cleanup; spec->mode_mask |= UNPRIV; + } else if (str_has_pfx(s, TEST_TAG_LOAD_MODE_PFX)) { + val = s + sizeof(TEST_TAG_LOAD_MODE_PFX) - 1; + if (strcmp(val, "jited") == 0) { + load_mask = JITED; + } else if (strcmp(val, "no_jited") == 0) { + load_mask = NO_JITED; + } else { + PRINT_FAIL("bad load spec: '%s'", val); + err = -EINVAL; + goto cleanup; + } } }
spec->arch_mask = arch_mask ?: -1; + spec->load_mask = load_mask ?: (JITED | NO_JITED);
if (spec->mode_mask == 0) spec->mode_mask = PRIV; @@ -928,6 +948,7 @@ void run_subtest(struct test_loader *tester, bool unpriv) { struct test_subspec *subspec = unpriv ? &spec->unpriv : &spec->priv; + int current_runtime = is_jit_enabled() ? JITED : NO_JITED; struct bpf_program *tprog = NULL, *tprog_iter; struct bpf_link *link, *links[32] = {}; struct test_spec *spec_iter; @@ -946,6 +967,11 @@ void run_subtest(struct test_loader *tester, return; }
+ if ((current_runtime & spec->load_mask) == 0) { + test__skip(); + return; + } + if (unpriv) { if (!can_execute_unpriv(tester, spec)) { test__skip();
Added test cases to ensure that programs with stack sizes exceeding 512 bytes are restricted in non-JITed mode, and can be executed normally in JITed mode, even with stack sizes exceeding 512 bytes due to the presence of may_goto instructions.
Test result: echo "0" > /proc/sys/net/core/bpf_jit_enable ./test_progs -t verifier_stack_ptr ... stack size 512 with may_goto with jit:SKIP stack size 512 with may_goto without jit:OK ... Summary: 1/27 PASSED, 25 SKIPPED, 0 FAILED
echo "1" > /proc/sys/net/core/bpf_jit_enable ./test_progs -t verifier_stack_ptr ... stack size 512 with may_goto with jit:OK stack size 512 with may_goto without jit:SKIP ... Summary: 1/27 PASSED, 25 SKIPPED, 0 FAILED
Signed-off-by: Jiayuan Chen mrpre@163.com --- .../selftests/bpf/progs/verifier_stack_ptr.c | 52 +++++++++++++++++++ 1 file changed, 52 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_ptr.c b/tools/testing/selftests/bpf/progs/verifier_stack_ptr.c index 417c61cd4b19..24aabc6083fd 100644 --- a/tools/testing/selftests/bpf/progs/verifier_stack_ptr.c +++ b/tools/testing/selftests/bpf/progs/verifier_stack_ptr.c @@ -481,4 +481,56 @@ l1_%=: r0 = 42; \ : __clobber_all); }
+SEC("socket") +__description("PTR_TO_STACK stack size > 512") +__failure __msg("invalid write to stack R1 off=-520 size=8") +__naked void stack_check_size_gt_512(void) +{ + asm volatile (" \ + r1 = r10; \ + r1 += -520; \ + r0 = 42; \ + *(u64*)(r1 + 0) = r0; \ + exit; \ +" ::: __clobber_all); +} + +#ifdef __BPF_FEATURE_MAY_GOTO +SEC("socket") +__description("PTR_TO_STACK stack size 512 with may_goto with jit") +__load_if_JITed() +__success __retval(42) +__naked void stack_check_size_512_with_may_goto_jit(void) +{ + asm volatile (" \ + r1 = r10; \ + r1 += -512; \ + r0 = 42; \ + *(u32*)(r1 + 0) = r0; \ + may_goto l0_%=; \ + r2 = 100; \ + l0_%=: \ + exit; \ +" ::: __clobber_all); +} + +SEC("socket") +__description("PTR_TO_STACK stack size 512 with may_goto without jit") +__load_if_no_JITed() +__failure __msg("stack size 520(extra 8) is too large") +__naked void stack_check_size_512_with_may_goto(void) +{ + asm volatile (" \ + r1 = r10; \ + r1 += -512; \ + r0 = 42; \ + *(u32*)(r1 + 0) = r0; \ + may_goto l0_%=; \ + r2 = 100; \ + l0_%=: \ + exit; \ +" ::: __clobber_all); +} +#endif + char _license[] SEC("license") = "GPL";
Hello:
This series was applied to bpf/bpf-next.git (master) by Alexei Starovoitov ast@kernel.org:
On Fri, 14 Feb 2025 17:18:20 +0800 you wrote:
Syzbot caught an array out-of-bounds bug [1]. It turns out that when the BPF program runs through do_misc_fixups(), it allocates an extra 8 bytes on the call stack, which eventually causes stack_depth to exceed 512.
I was able to reproduce this issue probabilistically by enabling CONFIG_UBSAN=y and disabling CONFIG_BPF_JIT_ALWAYS_ON with the selfttest I provide in second patch(although it doesn't happen every time - I didn't dig deeper into why UBSAN behaves this way).
[...]
Here is the summary with links: - [bpf-next,v3,1/3] bpf: Fix array bounds error with may_goto https://git.kernel.org/bpf/bpf-next/c/6ebc5030e0c5 - [bpf-next,v3,2/3] selftests/bpf: Introduce __load_if_JITed annotation for tests https://git.kernel.org/bpf/bpf-next/c/b38c72ab808c - [bpf-next,v3,3/3] selftests/bpf: Add selftest for may_goto https://git.kernel.org/bpf/bpf-next/c/72266ee83fed
You are awesome, thank you!
linux-kselftest-mirror@lists.linaro.org
-
Jiayuan Chen -
patchwork-bot+netdevbpf＠kernel.org