From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jakub Kicinski Subject: [RFCv2 06/16] bpf: verifier: recognize rN ^ rN as load of 0 Date: Fri, 26 Aug 2016 19:06:05 +0100 Message-ID: <1472234775-29453-7-git-send-email-jakub.kicinski@netronome.com> References: <1472234775-29453-1-git-send-email-jakub.kicinski@netronome.com> Cc: ast@kernel.org, daniel@iogearbox.net, dinan.gunawardena@netronome.com, jiri@resnulli.us, john.fastabend@gmail.com, kubakici@wp.pl, Jakub Kicinski To: netdev@vger.kernel.org Return-path: Received: from mail-wm0-f47.google.com ([74.125.82.47]:38641 "EHLO mail-wm0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752270AbcHZSPi (ORCPT ); Fri, 26 Aug 2016 14:15:38 -0400 Received: by mail-wm0-f47.google.com with SMTP id o80so3518571wme.1 for ; Fri, 26 Aug 2016 11:14:47 -0700 (PDT) In-Reply-To: <1472234775-29453-1-git-send-email-jakub.kicinski@netronome.com> Sender: netdev-owner@vger.kernel.org List-ID: Teach the verifier to recognize that xoring a register with itself makes it a constant (0). Signed-off-by: Jakub Kicinski --- 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