From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752342AbdJ0NcT (ORCPT ); Fri, 27 Oct 2017 09:32:19 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:9447 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752152AbdJ0NcS (ORCPT ); Fri, 27 Oct 2017 09:32:18 -0400 Message-ID: <59F334F0.2070900@huawei.com> Date: Fri, 27 Oct 2017 21:30:24 +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: Borislav Petkov CC: , , , , , , , , , , , 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> In-Reply-To: <20171027123348.GE1305@nazgul.tnic> Content-Type: text/plain; charset="UTF-8"; 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=0001.0A010205.59F33531.0016,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: cb85b4dac0c7dc576f91b169b4a958b7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017/10/27 20:33, 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. Yes, it's an out-of-tree module, loaded when boot kernel. register_kprobe() maybe not ready yet, but the bug is not caused by it obviously. > > 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. The smp_alt_modules is defined by LIST_HEAD, so it's initialized at start. A deleted list_head->next = LIST_POISON1 = 0xdead000000000000 + 0x100, then container_of() to get the struct smp_alt_module: -0x30 = 0xdead0000000000d0 Obviously, it's a deleted list_head, and I have explained clearly how it happen in the patch comment. Thanks. > Thx. >