Original code has a problem, cause following code failed to pass verifier:
r1 <- r10
r1 -= 8
r2 = 8
r3 = unsafe pointer
call BPF_FUNC_probe_read <-- R1 type=inv expected=fp
However, by replacing 'r1 -= 8' to 'r1 += -8' the above program can be
loaded successfully.
This is because the verifier allows only BPF_ADD instruction on a
FRAME_PTR reigster to forge PTR_TO_STACK register, but makes BPF_SUB
on FRAME_PTR reigster to get a UNKNOWN_VALUE register.
This patch fix it by adding BPF_SUB in stack_relative checking.
Signed-off-by: Wang Nan <wangn...@huawei.com>
---
kernel/bpf/verifier.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a251cf6..6dbdeba 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1020,7 +1020,8 @@ static int check_alu_op(struct reg_state *regs, struct
bpf_insn *insn)
}
/* pattern match 'bpf_add Rx, imm' instruction */
- if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
+ if (opcode == BPF_ADD && opcode == BPF_SUB &&
+ BPF_CLASS(insn->code) == BPF_ALU64 &&
regs[insn->dst_reg].type == FRAME_PTR &&
BPF_SRC(insn->code) == BPF_K)
stack_relative = true;
--
1.8.3.4
--
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