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 S1757332AbbCMQPL (ORCPT <rfc822;w@1wt.eu>);
	Fri, 13 Mar 2015 12:15:11 -0400
Received: from mail.skyhub.de ([78.46.96.112]:34419 "EHLO mail.skyhub.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1753839AbbCMQPH (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 13 Mar 2015 12:15:07 -0400
Date: Fri, 13 Mar 2015 17:13:38 +0100
From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>, Andi Kleen <andi@firstfloor.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Al Viro <viro@zeniv.linux.org.uk>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals
 delivered to 64-bit programs
Message-ID: <20150313161338.GC30678@pd.tnic>
References: <cover.1426193719.git.luto@kernel.org>
 <405594361340a2ec32f8e2b115c142df0e180d8e.1426193719.git.luto@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <405594361340a2ec32f8e2b115c142df0e180d8e.1426193719.git.luto@kernel.org>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Mar 12, 2015 at 01:57:51PM -0700, Andy Lutomirski wrote:
> From: Andy Lutomirski <luto@amacapital.net>
> 
> The comment in the signal code says that apps can save/restore other
> segments on their own.  It's true that apps can *save* SS on their
> own, but there's no way for apps to restore it: SYSCALL effectively
> resets SS to __USER_DS, so any value that user code tries to load
> into SS gets lost on entry to sigreturn.
> 
> This recycles two padding bytes in the segment selector area for SS.
> 
> While we're at it, we need a second change to make this useful.  If
> the signal we're delivering is caused by a bad SS value, saving that
> value isn't enough.  We need to remove that bad value from the regs
> before we try to deliver the signal.  Oddly, x32 already got this
> right.
> 
> I suspect that 64-bit programs that try to run 16-bit code and use
> signals will have a lot of trouble without this.
> 
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>

Acked-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--