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authorAndrii Nakryiko2024-04-04 14:45:35 -0700
committerAlexei Starovoitov2024-04-04 18:31:08 -0700
commit1f2a74b41ea8b902687eb97c4e7e3f558801865b (patch)
tree118282cc4c739cc119bf3428482f8433f9b72317
parentf91717007217d975aa975ddabd91ae1a107b9bff (diff)
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.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ffaa9f7f153c..41446bea8fab 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
*/