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 S1753193AbbJNRBv (ORCPT <rfc822;w@1wt.eu>);
	Wed, 14 Oct 2015 13:01:51 -0400
Received: from mail-lf0-f52.google.com ([209.85.215.52]:34189 "EHLO
	mail-lf0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751126AbbJNRBu (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 14 Oct 2015 13:01:50 -0400
Date: Wed, 14 Oct 2015 20:01:46 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Stas Sergeev <stsp@list.ru>
Cc: Andy Lutomirski <luto@kernel.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>, Pavel Emelyanov <xemul@parallels.com>
Subject: Re: [RFC 3/4] x86/signal/64: Re-add support for SS in the 64-bit
 signal context
Message-ID: <20151014170146.GU2048@uranus>
References: <cover.1444697927.git.luto@kernel.org>
 <6e14e2f7ce1c38fc1996bd4d5d3d9dc70b8bd94d.1444697927.git.luto@kernel.org>
 <20151014164021.GS2048@uranus>
 <561E895E.7050905@list.ru>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <561E895E.7050905@list.ru>
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

On Wed, Oct 14, 2015 at 07:57:02PM +0300, Stas Sergeev wrote:
...
> > correct? This should work for us. Stas, mind to refresh my memory,
> > which ss value doesmu setups here?
>
> Nothing.
> Older dosemus didn't care about touching __pad0, so
> whatever kernel saves there, is still there, even when
> dosemu needs another value.
> The problem starts to happen IIRC when dosemu invalidates
> the LDT entry that was previously saved by the kernel as an SS.
> IIRC this was causing the SIGSEGV right from sigreturn().
> It is actually a bit annoying to have such bad code in kernel
> only for the sake of the older dosemu.

I see. Thanks a huge for info!