From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753354AbbJaLvG (ORCPT <rfc822;w@1wt.eu>);
	Sat, 31 Oct 2015 07:51:06 -0400
Received: from fallback4.mail.ru ([94.100.181.169]:33419 "EHLO
	fallback4.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752335AbbJaLvB (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 31 Oct 2015 07:51:01 -0400
Subject: Re: 4.3 regression: task_work corruption in vm86 mode?
To: Andy Lutomirski <luto@amacapital.net>, Brian Gerst <brgerst@gmail.com>
References: <CALCETrUY51E290QYob+RMoKAzJCfo+y5-D2nithM1Bo2zOwoMw@mail.gmail.com>
 <CALCETrWUmL5bPyxR0gvchtn433hdnSqOuRdBjFsqJqa_xbtBnw@mail.gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>,
        Stas Sergeev <stsp@users.sourceforge.net>
From: Stas Sergeev <stsp@list.ru>
Message-ID: <5634AB0E.3060707@list.ru>
Date: Sat, 31 Oct 2015 14:50:38 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.3.0
MIME-Version: 1.0
In-Reply-To: <CALCETrWUmL5bPyxR0gvchtn433hdnSqOuRdBjFsqJqa_xbtBnw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Mras: Ok
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

31.10.2015 08:43, Andy Lutomirski пишет:
> On Fri, Oct 30, 2015 at 6:44 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> Hi all-
>>
>> In 4.3-rc7, running dosemu2 (https://github.com/stsp/dosemu2/) oopses
>> the system very quickly, as long as CONFIG_VM86=y.  It blows up
>> because snd_seq_delete_port walks ports_list_head, finds two valid
>> ports, and then starts finding obviously invalid pointers in the list.
>>
>> git bisect blames:
>>
>> commit 5ed92a8ab71f8865ba07811429c988c72299b315
>> Author: Brian Gerst <brgerst@gmail.com>
>> Date:   Wed Jul 29 01:41:19 2015 -0400
>>
>>      x86/vm86: Use the normal pt_regs area for vm86
>>
>> I haven't spotted the problem yet.  It seems to happen when
>> task_work_run fires in get_signal, which happens before
>> save_v86_state.  I'm not entirely sure what causes task work to be
>> scheduled at all while in v86 land.  Could we somehow be processing
>> task_work later than we should?
>>
> Nope, the bug has nothing to do with task_work.  Patches sent.
Andy, thanks for finally fixing this attack surface!
So after all, the comments you put into Kconfig, were justified.
Now I can seriously consider the dosemu2-specific vm86-light.
Having the machine to crash, was not a good starting point for
the clean-ups.
Also there is an interesting thread here:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1499089
I wonder if they are affected now by that bug or not...