From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751445AbdJ1B1g (ORCPT ); Fri, 27 Oct 2017 21:27:36 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:9529 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750851AbdJ1B1d (ORCPT ); Fri, 27 Oct 2017 21:27:33 -0400 Message-ID: <59F3DCE0.1080108@huawei.com> Date: Sat, 28 Oct 2017 09:26:56 +0800 From: zhouchengming User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Peter Zijlstra CC: Borislav Petkov , , , , , , , , , , , Subject: Re: [PATCH] kprobes, x86/alternatives: use text_mutex to protect smp_alt_modules References: <1509096884-22993-1-git-send-email-zhouchengming1@huawei.com> <20171027111527.GD1305@nazgul.tnic> <59F31BB5.90905@huawei.com> <20171027123348.GE1305@nazgul.tnic> <20171027141502.GA3165@worktop.lehotels.local> In-Reply-To: <20171027141502.GA3165@worktop.lehotels.local> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.236.183] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090203.59F3DCE9.0034,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 513f511b97ff327a9e3858ac7e2aafb9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017/10/27 22:15, Peter Zijlstra wrote: > On Fri, Oct 27, 2017 at 02:33:48PM +0200, Borislav Petkov wrote: >> On Fri, Oct 27, 2017 at 07:42:45PM +0800, zhouchengming wrote: >>> This is a real bug happened on one of our machines, below is the calltrace. >>> We can see the trigger is at alternatives_text_reserved+0x20/0x80, and >>> encounter a deleted (poisoned) list_head. >> Looks like some out-of-tree, old kernel thing. We don't have >> mlx4_stats_sysfs_create() upstream and looking at the boot timestamps, >> it could be that register_jprobe() is not ready yet. >> >> Looking at the Code, though: >> >> 20: 74 59 je 0x7b >> 22: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1) >> 29: 00 00 >> 2b:* 48 3b 71 20 cmp 0x20(%rcx),%rsi<-- trapping instruction >> 2f: 72 3a jb 0x6b >> 31: 48 3b 79 28 cmp 0x28(%rcx),%rdi >> 35: 77 34 ja 0x6b >> >> %rcx is 0xdead0000000000d0 and that is POISON_POINTER_DELTA + 0xd0 so >> that looks more like smp_alt_modules is not initialized yet but I could >> could very well be wrong because this is an old kernel. So trigger that >> with the upstream kernel without out of tree modules. > Not to mention that we're about (or just have) yanked jprobes out of the > kernel entirely. Well... but this is a bug of alternatives_text_reserved(), it traverse the list without holding the smp_alt mutex. So all users of it, like kprobes, will still have this problem. Maybe I could think of a way to get rid of the mutex entirely. Thanks. > . >