From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753947AbbAOMh4 (ORCPT ); Thu, 15 Jan 2015 07:37:56 -0500 Received: from mail9.hitachi.co.jp ([133.145.228.44]:42194 "EHLO mail9.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753219AbbAOMhy (ORCPT ); Thu, 15 Jan 2015 07:37:54 -0500 Message-ID: <54B7B49C.90003@hitachi.com> Date: Thu, 15 Jan 2015 21:37:48 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Andy Lutomirski Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Dave Hansen Subject: Re: [PATCH 3.19 v4 2/2] x86: Enforce maximum instruction size in the instruction decoder References: <6ceb805aba0291431f19f72d7f2e765f3a0a9fcf.1421183147.git.luto@amacapital.net> In-Reply-To: <6ceb805aba0291431f19f72d7f2e765f3a0a9fcf.1421183147.git.luto@amacapital.net> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2015/01/14 6:49), Andy Lutomirski wrote: > x86 instructions cannot exceed 15 bytes, and the instruction decoder > should enforce that. Prior to 6ba48ff46f76, the instruction length > limit was implicitly set to 16, which was an approximation of 15, > but there is currently no limit at all. > > Fix the decoder to reject instructions that exceed 15 bytes. > A subsequent patch (targetted for 3.20) will fix MAX_INSN_SIZE. Hmm, is there any problem to just change MAX_INSN_SIZE to 15? > Other than potentially confusing some of the decoder sanity checks, > I'm not aware of any actual problems that omitting this check would > cause. > > Fixes: 6ba48ff46f76 x86: Remove arbitrary instruction size limit in instruction decoder > Signed-off-by: Andy Lutomirski > --- > arch/x86/lib/insn.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c > index 2480978b31cc..7b80745d2c5a 100644 > --- a/arch/x86/lib/insn.c > +++ b/arch/x86/lib/insn.c > @@ -52,6 +52,13 @@ > */ > void insn_init(struct insn *insn, const void *kaddr, int buf_len, int x86_64) > { > + /* > + * Instructions longer than 15 bytes are invalid even if the > + * input buffer is long enough to hold them. > + */ > + if (buf_len > 15) > + buf_len = 15; > + Without changing the MAX_INSN_SIZE, this looks very odd, since all other code suppose that the max length of an instruction is 16 (MAX_INSN_SIZE) except here. Thank you, > memset(insn, 0, sizeof(*insn)); > insn->kaddr = kaddr; > insn->end_kaddr = kaddr + buf_len; > -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com