From 226b46d53bb8e1d49fc541d7851c09ab04d782b9 Mon Sep 17 00:00:00 2001 From: Shung-Hsi Yu Date: Thu, 2 Nov 2023 13:39:03 +0800 Subject: [PATCH] bpf: Fix precision tracking for BPF_ALU | BPF_TO_BE | BPF_END MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit commit 291d044fd51f8484066300ee42afecf8c8db7b3a upstream. BPF_END and BPF_NEG has a different specification for the source bit in the opcode compared to other ALU/ALU64 instructions, and is either reserved or use to specify the byte swap endianness. In both cases the source bit does not encode source operand location, and src_reg is a reserved field. backtrack_insn() currently does not differentiate BPF_END and BPF_NEG from other ALU/ALU64 instructions, which leads to r0 being incorrectly marked as precise when processing BPF_ALU | BPF_TO_BE | BPF_END instructions. This commit teaches backtrack_insn() to correctly mark precision for such case. While precise tracking of BPF_NEG and other BPF_END instructions are correct and does not need fixing, this commit opt to process all BPF_NEG and BPF_END instructions within the same if-clause to better align with current convention used in the verifier (e.g. check_alu_op). Fixes: b5dc0163d8fd ("bpf: precise scalar_value tracking") Cc: stable@vger.kernel.org Reported-by: Mohamed Mahmoud Closes: https://lore.kernel.org/r/87jzrrwptf.fsf@toke.dk Tested-by: Toke Høiland-Jørgensen Tested-by: Tao Lyu Acked-by: Eduard Zingerman Signed-off-by: Shung-Hsi Yu Link: https://lore.kernel.org/r/20231102053913.12004-2-shung-hsi.yu@suse.com Signed-off-by: Alexei Starovoitov Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 173a8ae..824531d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3444,7 +3444,12 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx, if (class == BPF_ALU || class == BPF_ALU64) { if (!bt_is_reg_set(bt, dreg)) return 0; - if (opcode == BPF_MOV) { + if (opcode == BPF_END || opcode == BPF_NEG) { + /* sreg is reserved and unused + * dreg still need precision before this insn + */ + return 0; + } else if (opcode == BPF_MOV) { if (BPF_SRC(insn->code) == BPF_X) { /* dreg = sreg or dreg = (s8, s16, s32)sreg * dreg needs precision after this insn -- 2.7.4