Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752497AbdDDCCb (ORCPT ); Mon, 3 Apr 2017 22:02:31 -0400 Received: from mga07.intel.com ([134.134.136.100]:49416 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751647AbdDDCCa (ORCPT ); Mon, 3 Apr 2017 22:02:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,273,1486454400"; d="scan'208";a="1130535094" Message-ID: <1491271348.2647.69.camel@ranerica-desktop> Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention From: Ricardo Neri To: Alexandre Julliard Cc: Stas Sergeev , Andy Lutomirski , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , Peter Zijlstra , Andrew Morton , Brian Gerst , Chris Metcalf , Dave Hansen , Paolo Bonzini , Masami Hiramatsu , Huang Rui , Jiri Slaby , Jonathan Corbet , "Michael S. Tsirkin" , Paul Gortmaker , Vlastimil Babka , Chen Yucong , Fenghua Yu , "Ravi V. Shankar" , Shuah Khan , "linux-kernel@vger.kernel.org" , X86 ML , linux-msdos@vger.kernel.org, wine-devel@winehq.org Date: Mon, 03 Apr 2017 19:02:28 -0700 In-Reply-To: <87vaqppmc1.fsf@winehq.org> References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <79ba0fff-4c01-2bfa-06cb-5cfc98dd710c@list.ru> <997ba581-ecfa-b773-a48e-85b92a439836@list.ru> <1489022122.131264.33.camel@ranerica-desktop> <63231222-5b42-c8c9-02f0-0afbe702d8b5@list.ru> <1489190396.131264.47.camel@ranerica-desktop> <6331deea-e9b0-fcfe-b75d-8100f37a615a@list.ru> <1490658399.2647.14.camel@ranerica-desktop> <1490762284.2647.24.camel@ranerica-desktop> <2a9c7bfd-e85c-2673-d3b5-906fe7dd8db4@list.ru> <1490850848.2647.28.camel@ranerica-desktop> <3f1f1632-ae64-34f7-70ef-d4f8091cd5c1@list.ru> <1490924035.2647.35.camel@ranerica-desktop> <87vaqppmc1.fsf@winehq.org> 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: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3098 Lines: 66 On Fri, 2017-03-31 at 16:11 +0200, Alexandre Julliard wrote: > Ricardo Neri writes: > > > On Thu, 2017-03-30 at 13:10 +0300, Stas Sergeev wrote: > >> 30.03.2017 08:14, Ricardo Neri пишет: > >> >>>> But at least dosemu implements it, so probably it is needed. > >> >>> Right. > >> >>> > >> >>>> Of course if it is used by one of 100 DOS progs, then there > >> >>>> is an option to just add its support to dosemu2 and pretend > >> >>>> the compatibility problems did not exist. :) > >> >>> Do you mean relaying the GP fault to dosemu instead of trapping it and > >> >>> emulating it in the kernel? > >> >> Yes, that would be optimal if this does not severely break > >> >> the current setups. If we can find out that smsw is not in > >> >> the real use, we can probably do exactly that. > >> >> But other > >> >> instructions are not in real use in v86 for sure, so I > >> >> wouldn't be adding the explicit test-cases to the kernel > >> >> that will make you depend on some particular behaviour > >> >> that no one may need. > >> >> My objection was that we shouldn't > >> >> write tests before we know exactly how we want this to work. > >> > OK, if only SMSW is used then I'll keep the emulation for SMSW only. > >> In fact, smsw has an interesting property, which is that > >> no one will ever want to disable its in-kernel emulation > >> to provide its own. > >> So while I'll try to estimate its usage, emulating it in kernel > >> will not be that problematic in either case. > > > > Ah good to know! > > > >> As for protected mode, if wine only needs sgdt/sidt, then > >> again, no one will want to disable its emulation. Not the > >> case with sldt, but AFAICS wine doesn't need sldt, and so > >> we can leave sldt without a fixups. Is my understanding > >> correct? > > > > This is my understanding as well. I could not find any use of sldt in > > wine. Alexandre, would you mind confirming? > > Some versions of the Themida software protection are known to use sldt > as part of the virtual machine detection code [1]. The check currently > fails because it expects the LDT to be zero, so the app is already > broken, but sldt segfaulting would still cause a crash where there > wasn't one before. > > However, I'm only aware of one application using this, and being able to > catch and emulate sldt ourselves would actually give us a chance to fix > this app in newer Wine versions, so I'm not opposed to having it > segfault. Great! Then this is in line with what we are aiming to do with dosemu2: not emulate str and sldt. > > In fact it would be nice to be able to make sidt/sgdt/etc. segfault > too. I know a new syscall is a pain, but as far as Wine is concerned, > being able to opt out from any emulation would be potentially useful. I see. I guess for now there should not be a problem with emulating sidt/sgdt/smsw, right? In this way we don't break current versions of winehq and programs using it. In a phase two we can introduce the syscall so that kernel fixups can be disabled. Does this make sense? Thanks and BR, Ricardo