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| author | Eduard Zingerman <eddyz87@gmail.com> | 2026-08-26 11:18:45 -0700 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-08-26 18:45:32 -0700 |
| commit | ce6dcd0aed185432d02cafc82b738318af257ccd (patch) | |
| tree | c2865fd5dcfd40b065bb3af011aa50c939ad56f7 | |
| parent | d3ef6c097ba078e1f8c7239d76a0ce8b61e75095 (diff) | |
| download | linux-ce6dcd0aed185432d02cafc82b738318af257ccd.tar.gz linux-ce6dcd0aed185432d02cafc82b738318af257ccd.zip | |
selftests/bpf: a demo for check_cond_jmp_op() non-null inference bug
A comparison between PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED and
PTR_TO_MAP_VALUE_OR_NULL should not infer that map pointer is not null.
A bug in check_cond_jmp_op() made such inference possible.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260826-bug-029-bad-non-null-inference-v2-2-136789ace9e9@localhost
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
| -rw-r--r-- | tools/testing/selftests/bpf/progs/verifier_jeq_infer_not_null.c | 52 |
1 files changed, 52 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 3d1e8de4390c..b412a542ef76 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 @@ -3,7 +3,9 @@ #include <linux/bpf.h> #include <bpf/bpf_helpers.h> +#include <stdbool.h> #include "bpf_misc.h" +#include "bpf_kfuncs.h" struct { __uint(type, BPF_MAP_TYPE_XSKMAP); @@ -12,6 +14,13 @@ struct { __type(value, int); } map_xskmap SEC(".maps"); +struct { + __uint(type, BPF_MAP_TYPE_HASH); + __uint(max_entries, 1); + __type(key, int); + __type(value, int); +} map_hash SEC(".maps"); + /* This is equivalent to the following program: * * r6 = skb->sk; @@ -264,4 +273,47 @@ __naked void jne_reg_reg_null_check(void) : __clobber_all); } +/* + * A comparison between PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED and + * PTR_TO_MAP_VALUE_OR_NULL should not infer that map pointer is not null. + * A bug in check_cond_jmp_op() made such inference possible. + */ +SEC("raw_tp") +__failure +__msg("error: invalid dereference of R0 (a nullable map value pointer)") +__msg(">>> 11 | (61) r0 = *(u32 *)(r0 +0)") +__naked void untrusted_mem_does_not_infer_map_value_non_null(void) +{ + asm volatile (" \ + /* r6 = bpf_rdonly_cast(0, 0); */ \ + r1 = 0; \ + r2 = 0; \ + call %[bpf_rdonly_cast]; \ + r6 = r0; \ + /* 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]; \ + /* \ + * buggy verifier assumed that r6 can't be null \ + * and marked r0 non-null as well. \ + */ \ + if r6 != r0 goto 1f; \ + r0 = *(u32 *)(r0 + 0); \ +1: r0 = 0; \ + exit; \ +" : + : __imm(bpf_rdonly_cast), + __imm(bpf_map_lookup_elem), + __imm_addr(map_hash) + : __clobber_all); +} + +void kfunc_root(void) +{ + bpf_rdonly_cast(0, 0); +} + char _license[] SEC("license") = "GPL"; |