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bpf: Fix precision tracking for BPF_ALU | BPF_TO_BE | BPF_END
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: b5dc0163d8
("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>
Link: https://lore.kernel.org/r/20231102053913.12004-2-shung-hsi.yu@suse.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
parent
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@ -3742,7 +3742,12 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx, int subseq_idx,
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if (class == BPF_ALU || class == BPF_ALU64) {
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if (!bt_is_reg_set(bt, dreg))
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return 0;
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if (opcode == BPF_MOV) {
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if (opcode == BPF_END || opcode == BPF_NEG) {
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/* sreg is reserved and unused
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* dreg still need precision before this insn
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*/
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return 0;
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} else if (opcode == BPF_MOV) {
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if (BPF_SRC(insn->code) == BPF_X) {
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/* dreg = sreg or dreg = (s8, s16, s32)sreg
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* dreg needs precision after this insn
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