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 because their source bit are unset and
thus treated as the BPF_K case, this commit opt to process all BPF_NEG
and BPF_END instructions within the same if-clause so it better aligns
with current convention used in the verifier (e.g. check_alu_op).
Fixes: b5dc0163d8fd ("bpf: precise scalar_value tracking")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Mohamed Mahmoud <mmahmoud@xxxxxxxxxx>
Tested-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Tested-by: Tao Lyu <tao.lyu@xxxxxxx>
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
---
kernel/bpf/verifier.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 873ade146f3d..646dc49263fd 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
--
2.42.0
