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 mmahmoud@redhat.com Closes: https://lore.kernel.org/r/87jzrrwptf.fsf@toke.dk Tested-by: Toke Høiland-Jørgensen toke@redhat.com Tested-by: Tao Lyu tao.lyu@epfl.ch Acked-by: Eduard Zingerman eddyz87@gmail.com Signed-off-by: Shung-Hsi Yu shung-hsi.yu@suse.com --- 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 873ade146f3d..ba9aee3a4269 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3426,7 +3426,12 @@ 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