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 S1752678AbdBMTak (ORCPT <rfc822;w@1wt.eu>);
        Mon, 13 Feb 2017 14:30:40 -0500
Received: from mail-wm0-f68.google.com ([74.125.82.68]:33503 "EHLO
        mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751617AbdBMTaj (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 13 Feb 2017 14:30:39 -0500
Date: Mon, 13 Feb 2017 20:30:34 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>, Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@suse.de>, X86 ML <x86@kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>
Subject: Re: [PATCHv3] x86/selftests: add clobbers for int80 on x86_64
Message-ID: <20170213193034.GA12346@gmail.com>
References: <20170213101336.20486-1-dsafonov@virtuozzo.com>
 <CALCETrXuN3zOTKTScas+Tj=7Xzm_DTEDyuL-toxp=4+i-=HX6w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALCETrXuN3zOTKTScas+Tj=7Xzm_DTEDyuL-toxp=4+i-=HX6w@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Andy Lutomirski <luto@amacapital.net> wrote:

> On Mon, Feb 13, 2017 at 2:13 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
> > Kernel erases R8..R11 registers prior returning to userspace
> > from int80: https://lkml.org/lkml/2009/10/1/164
> >
> > GCC can reuse this registers and doesn't expect them to change
> > during syscall invocation. I met this kind of bug in CRIU once
> > gcc 6.1 and clang stored local variables in those registers
> > and the kernel zerofied them during syscall:
> > https://github.com/xemul/criu/commit/990d33f1a1cdd17bca6c2eb059ab3be2564f7fa2
> >
> > By that reason I suggest to add those registers to clobbers
> > in selftests.  Also, as notted by Andy - removed unneeded clobber
> > for flags in int 0x80 inline asm.
> 
> Acked-by: Andy Lutomirski <luto@kernel.org>
> 
> Although these days we could preserve these regs in the kernel at the cost of (I 
> think) 4 bytes of text and zero runtime overhead.

I think we should try that...

Thanks,

	Ingo