6.8-stable review patch. If anyone has any objections, please let me know.
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From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit 1f2a74b41ea8b902687eb97c4e7e3f558801865b ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 11bc3af33f34f..68ec508057466 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3584,7 +3584,8 @@ 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. @@ -3600,7 +3601,8 @@ 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 */