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| author | Andrii Nakryiko <andrii@kernel.org> | 2024-04-04 14:45:35 -0700 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2024-04-04 18:31:08 -0700 |
| commit | 1f2a74b41ea8b902687eb97c4e7e3f558801865b (patch) | |
| tree | 118282cc4c739cc119bf3428482f8433f9b72317 | |
| parent | f91717007217d975aa975ddabd91ae1a107b9bff (diff) | |
| download | bpf-next-1f2a74b41ea8b902687eb97c4e7e3f558801865b.tar.gz | |
bpf: prevent r10 register from being marked as precise
r10 is a special register that is not under BPF program's control and is
always effectively precise. The rest of precision logic assumes that
only r0-r9 SCALAR registers are marked as precise, so prevent r10 from
being marked precise.
This can happen due to signed cast instruction allowing to do something
like `r0 = (s8)r10;`, which later, if r0 needs to be precise, would lead
to an attempt to mark r10 as precise.
Prevent this with an extra check during instruction backtracking.
Fixes: 8100928c8814 ("bpf: Support new sign-extension mov insns")
Reported-by: syzbot+148110ee7cf72f39f33e@syzkaller.appspotmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240404214536.3551295-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
| -rw-r--r-- | kernel/bpf/verifier.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ffaa9f7f153cfd..41446bea8fabf1 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3615,7 +3615,8 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx, * sreg needs precision before this insn */ bt_clear_reg(bt, dreg); - bt_set_reg(bt, sreg); + if (sreg != BPF_REG_FP) + bt_set_reg(bt, sreg); } else { /* dreg = K * dreg needs precision after this insn. @@ -3631,7 +3632,8 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx, * both dreg and sreg need precision * before this insn */ - bt_set_reg(bt, sreg); + if (sreg != BPF_REG_FP) + bt_set_reg(bt, sreg); } /* else dreg += K * dreg still needs precision before this insn */ |