Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933427AbdCaOvo convert rfc822-to-8bit (ORCPT ); Fri, 31 Mar 2017 10:51:44 -0400 Received: from wine.codeweavers.com ([209.46.25.134]:44645 "EHLO winehq.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933358AbdCaOvd (ORCPT ); Fri, 31 Mar 2017 10:51:33 -0400 X-Greylist: delayed 2355 seconds by postgrey-1.27 at vger.kernel.org; Fri, 31 Mar 2017 10:51:33 EDT From: Alexandre Julliard To: Ricardo Neri 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 Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention In-Reply-To: <1490924035.2647.35.camel@ranerica-desktop> (Ricardo Neri's message of "Thu, 30 Mar 2017 18:33:55 -0700") 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> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) Date: Fri, 31 Mar 2017 16:11:58 +0200 Message-ID: <87vaqppmc1.fsf@winehq.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Spam-Score: -2.9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2650 Lines: 60 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. 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. [1] https://www.winehq.org/pipermail/wine-bugs/2008-February/094470.html -- Alexandre Julliard julliard@winehq.org