[RFCv2 06/16] bpf: verifier: recognize rN ^ rN as load of 0
From: Jakub Kicinski <hidden>
Date: 2016-08-26 18:15:38
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
Teach the verifier to recognize that xoring a register with itself makes it a constant (0). Signed-off-by: Jakub Kicinski <redacted> --- kernel/bpf/verifier.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index db68a0e5db1e..0f4494c194f9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c@@ -1550,6 +1550,12 @@ static int check_alu_op(struct verifier_env *env, struct bpf_insn *insn) verbose("invalid BPF_ALU opcode %x\n", opcode); return -EINVAL; + } else if (opcode == BPF_XOR && BPF_SRC(insn->code) == BPF_X && + insn->src_reg == insn->dst_reg) { + + regs[insn->dst_reg].type = CONST_IMM; + regs[insn->dst_reg].imm = 0; + } else { /* all other ALU ops: and, sub, xor, add, ... */ if (BPF_SRC(insn->code) == BPF_X) {
--
1.9.1