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| author | Eduard Zingerman <eddyz87@gmail.com> | 2026-09-04 01:33:19 -0700 |
|---|---|---|
| committer | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2026-09-04 12:58:02 +0200 |
| commit | 6752b90ccfb378e311e428932facf37c8625abae (patch) | |
| tree | 3a0bee174e08b3b2f5bc3e46bd85d278b8c5a160 | |
| parent | 67b529f521a6676cdfc78b91b0217d7eaa84216b (diff) | |
| download | linux-6752b90ccfb378e311e428932facf37c8625abae.tar.gz linux-6752b90ccfb378e311e428932facf37c8625abae.zip | |
selftests/bpf: No non-NULL inference from unbounded offset pointers
Check that a comparison against a pointer whose offset is not bounded
from above does not make the verifier infer that a nullable pointer is
not NULL, and that a bounded offset still does. W/o the previous patch
the first test is accepted.
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/20260904083325.2083493-2-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 | 80 |
1 files changed, 80 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 b412a542ef76..8657e4a0d601 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 @@ -311,6 +311,86 @@ __naked void untrusted_mem_does_not_infer_map_value_non_null(void) : __clobber_all); } +/* + * A pointer with an offset that is not bounded from above may be null at + * runtime, hence it is not a witness for the pointer it is compared with. + */ +SEC("socket") +__failure +__msg("error: invalid dereference of R7 (a nullable map value pointer)") +__naked void unbounded_offset_does_not_infer_map_value_non_null(void) +{ + asm volatile (" \ + /* r6 = bpf_map_lookup_elem(map_hash, &0); */ \ + *(u64 *)(r10 - 8) = 0; \ + r1 = %[map_hash] ll; \ + r2 = r10; \ + r2 += -8; \ + call %[bpf_map_lookup_elem]; \ + if r0 == 0 goto 1f; \ + r6 = r0; \ + /* r7 = bpf_map_lookup_elem(map_hash, &1); */ \ + *(u64 *)(r10 - 8) = 1; \ + r1 = %[map_hash] ll; \ + r2 = r10; \ + r2 += -8; \ + call %[bpf_map_lookup_elem]; \ + r7 = r0; \ + /* pointer - pointer is an unknown scalar */ \ + r8 = r7; \ + r8 -= r6; \ + /* r8 is in [0, S64_MAX] */ \ + r8 <<= 1; \ + r8 >>= 1; \ + /* r6 may wrap to zero at runtime */ \ + r6 += r8; \ + if r7 != r6 goto 1f; \ + r0 = *(u8 *)(r7 + 0); \ +1: r0 = 0; \ + exit; \ +" : + : __imm(bpf_map_lookup_elem), + __imm_addr(map_hash) + : __clobber_all); +} + +/* Same, but the offset is bounded, so the inference is still done. */ +SEC("socket") +__success +__naked void bounded_offset_infers_map_value_non_null(void) +{ + asm volatile (" \ + /* r6 = bpf_map_lookup_elem(map_hash, &0); */ \ + *(u64 *)(r10 - 8) = 0; \ + r1 = %[map_hash] ll; \ + r2 = r10; \ + r2 += -8; \ + call %[bpf_map_lookup_elem]; \ + if r0 == 0 goto 1f; \ + r6 = r0; \ + /* r7 = bpf_map_lookup_elem(map_hash, &1); */ \ + *(u64 *)(r10 - 8) = 1; \ + r1 = %[map_hash] ll; \ + r2 = r10; \ + r2 += -8; \ + call %[bpf_map_lookup_elem]; \ + r7 = r0; \ + /* pointer - pointer is an unknown scalar */ \ + r8 = r7; \ + r8 -= r6; \ + /* r8 is in [0, 3] */ \ + r8 &= 3; \ + r6 += r8; \ + if r7 != r6 goto 1f; \ + r0 = *(u8 *)(r7 + 0); \ +1: r0 = 0; \ + exit; \ +" : + : __imm(bpf_map_lookup_elem), + __imm_addr(map_hash) + : __clobber_all); +} + void kfunc_root(void) { bpf_rdonly_cast(0, 0); |