Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754768AbdCIBrK (ORCPT <rfc822;w@1wt.eu>);
        Wed, 8 Mar 2017 20:47:10 -0500
Received: from mga09.intel.com ([134.134.136.24]:41502 "EHLO mga09.intel.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752465AbdCIBrI (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 8 Mar 2017 20:47:08 -0500
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.36,266,1486454400"; 
   d="scan'208";a="942226442"
Message-ID: <1489020399.131264.27.camel@ranerica-desktop>
Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention
From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Stas Sergeev <stsp@list.ru>
Cc: Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@suse.de>, Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Brian Gerst <brgerst@gmail.com>, Chris Metcalf <cmetcalf@mellanox.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>, Liang Z Li <liang.z.li@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>, Huang Rui <ray.huang@amd.com>,
        Jiri Slaby <jslaby@suse.cz>, Jonathan Corbet <corbet@lwn.net>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Vlastimil Babka <vbabka@suse.cz>, Chen Yucong <slaoub@gmail.com>,
        Alexandre Julliard <julliard@winehq.org>,
        Fenghua Yu <fenghua.yu@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Shuah Khan <shuah@kernel.org>, linux-kernel@vger.kernel.org,
        x86@kernel.org, linux-msdos@vger.kernel.org, wine-devel@winehq.org
Date: Wed, 08 Mar 2017 16:46:39 -0800
In-Reply-To: <79ba0fff-4c01-2bfa-06cb-5cfc98dd710c@list.ru>
References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com>
         <79ba0fff-4c01-2bfa-06cb-5cfc98dd710c@list.ru>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.10.4-0ubuntu2 
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1387
Lines: 35

On Wed, 2017-03-08 at 17:08 +0300, Stas Sergeev wrote:
> 08.03.2017 03:32, Ricardo Neri пишет:
> > These are the instructions covered by UMIP:
> > * SGDT - Store Global Descriptor Table
> > * SIDT - Store Interrupt Descriptor Table
> > * SLDT - Store Local Descriptor Table
> > * SMSW - Store Machine Status Word
> > * STR - Store Task Register
> >
> > This patchset initially treated tasks running in virtual-8086 mode as a
> > special case. However, I received clarification that DOSEMU[8] does not
> > support applications that use these instructions.
> Yes, this is the case.
> But at least in the past there was an attempt to
> support SLDT as it is used by an ancient pharlap
> DOS extender (currently unsupported by dosemu1/2).
> So how difficult would it be to add an optional
> possibility of delivering such SIGSEGV to userspace
> so that the kernel's dummy emulation can be overridden?

I suppose a umip=noemulation kernel parameter could be added in this
case.

> It doesn't need to be a matter of this particular
> patch set, i.e. this proposal should not trigger a
> v7 resend of all 21 patches. :) But it would be useful
> for the future development of dosemu2.

Would dosemu2 use 32-bit processes in order to keep segmentation? If it
could use 64-bit processes, emulation is not used in this case and the
SIGSEGV is delivered to user space.

Thanks and BR,
Ricardo