From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH bpf] bpf: fix 32-bit divide by zero Date: Thu, 18 Jan 2018 14:30:54 -0800 Message-ID: <1516314654.3606.28.camel@gmail.com> References: <20180113025952.3451758-1-ast@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: daniel@iogearbox.net, edumazet@google.com, netdev@vger.kernel.org, kernel-team@fb.com To: Alexei Starovoitov , davem@davemloft.net Return-path: Received: from mail-pf0-f195.google.com ([209.85.192.195]:34250 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754104AbeARWa5 (ORCPT ); Thu, 18 Jan 2018 17:30:57 -0500 Received: by mail-pf0-f195.google.com with SMTP id e76so15801018pfk.1 for ; Thu, 18 Jan 2018 14:30:57 -0800 (PST) In-Reply-To: <20180113025952.3451758-1-ast@kernel.org> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2018-01-12 at 18:59 -0800, Alexei Starovoitov wrote: > due to some JITs doing if (src_reg == 0) check in 64-bit mode > for div/mod opreations mask upper 32-bits of src register > before doing the check > Is the plan to fix JIT, and if they can all be fixed, revert this patch ? x86 patch would be something like : diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 87f214fbe66ec163d24b12b6defc7edab612ecc9..91e4ab69573e09f793eb1c1e29d1b5ffad1d5dc7 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -548,8 +548,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, if (BPF_SRC(insn->code) == BPF_X) { /* if (src_reg == 0) return 0 */ - /* cmp r11, 0 */ - EMIT4(0x49, 0x83, 0xFB, 0x00); + if (BPF_CLASS(insn->code) == BPF_ALU64) { + /* cmp r11, 0 */ + EMIT4(0x49, 0x83, 0xFB, 0x00); + } else { + /* cmp r11d, 0 */ + EMIT4(0x41, 0x83, 0xFB, 0x00); + } /* jne .+9 (skip over pop, pop, xor and jmp) */ EMIT2(X86_JNE, 1 + 1 + 2 + 5);