diff options
| author | Eduard Zingerman <eddyz87@gmail.com> | 2026-09-04 01:33:23 -0700 |
|---|---|---|
| committer | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2026-09-04 12:58:04 +0200 |
| commit | 836b2fe544a5e9b5ce116622cb36fba33838c6fd (patch) | |
| tree | 95e38e4aaa0a6a78e373148b3d0af4aa2ab3d371 | |
| parent | e51179a4e09846f8fd0f26a05068520de2b301bf (diff) | |
| download | linux-836b2fe544a5e9b5ce116622cb36fba33838c6fd.tar.gz linux-836b2fe544a5e9b5ce116622cb36fba33838c6fd.zip | |
selftests/bpf: Check that JMP32 pointer vs zero jumps are not predicted
Add jmp32_ptr_vs_zero_jne: the fall-through of the 32-bit compare, which
the verifier used to skip, contains an out of bounds map value access,
hence w/o the previous patch the program is accepted. See previous patch
for detailed description.
Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260904083325.2083493-6-eddyz87@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
| -rw-r--r-- | tools/testing/selftests/bpf/progs/verifier_jeq_infer_not_null.c | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/progs/verifier_jeq_infer_not_null.c b/tools/testing/selftests/bpf/progs/verifier_jeq_infer_not_null.c index 8657e4a0d601..410acbf658c7 100644 --- a/tools/testing/selftests/bpf/progs/verifier_jeq_infer_not_null.c +++ b/tools/testing/selftests/bpf/progs/verifier_jeq_infer_not_null.c @@ -391,6 +391,33 @@ __naked void bounded_offset_infers_map_value_non_null(void) : __clobber_all); } +/* + * The low 32 bits of a map value pointer may be zero, hence a 32-bit + * compare with zero cannot be predicted from the pointer being non-NULL + * and both successors of such a jump have to be verified. + */ +SEC("socket") +__failure __msg("invalid access to map value, value_size=4 off=32 size=4") +__naked void jmp32_ptr_vs_zero_jne(void) +{ + asm volatile (" \ + /* r0 = bpf_map_lookup_elem(map_hash, &key); */ \ + *(u64 *)(r10 - 8) = 0; \ + r1 = %[map_hash] ll; \ + r2 = r10; \ + r2 += -8; \ + call %[bpf_map_lookup_elem]; \ + if r0 == 0 goto 1f; \ + if w0 != 0 goto 1f; \ + r0 = *(u32 *)(r0 + 32); \ +1: r0 = 0; \ + exit; \ +" : + : __imm(bpf_map_lookup_elem), + __imm_addr(map_hash) + : __clobber_all); +} + void kfunc_root(void) { bpf_rdonly_cast(0, 0); |