From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932845AbdCKANW (ORCPT ); Fri, 10 Mar 2017 19:13:22 -0500 Received: from mga06.intel.com ([134.134.136.31]:43865 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755129AbdCKANN (ORCPT ); Fri, 10 Mar 2017 19:13:13 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,143,1486454400"; d="scan'208";a="66319930" Message-ID: <1489191190.131264.55.camel@ranerica-desktop> Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention From: Ricardo Neri To: Stas Sergeev Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , Peter Zijlstra , Andrew Morton , Brian Gerst , Chris Metcalf , Dave Hansen , Paolo Bonzini , Liang Z Li , Masami Hiramatsu , Huang Rui , Jiri Slaby , Jonathan Corbet , "Michael S. Tsirkin" , Paul Gortmaker , Vlastimil Babka , Chen Yucong , Alexandre Julliard , Fenghua Yu , "Ravi V. Shankar" , Shuah Khan , linux-kernel@vger.kernel.org, x86@kernel.org, linux-msdos@vger.kernel.org, wine-devel@winehq.org Date: Fri, 10 Mar 2017 16:13:10 -0800 In-Reply-To: References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <79ba0fff-4c01-2bfa-06cb-5cfc98dd710c@list.ru> <1489020399.131264.27.camel@ranerica-desktop> 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 On Sat, 2017-03-11 at 02:58 +0300, Stas Sergeev wrote: > 11.03.2017 02:47, Ricardo Neri пишет: > >> > >>>> 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. > >> It does use the mix: 64bit process but some segments > >> are 32bit for DOS code. > > Do you mean that dosemu2 will start as a 64-bit process and will jump to > > 32-bit code segments? > Yes, so the offending insns are executed only in 32bit > and 16bit segments, even if the process itself is 64bit. > I guess you handle 16bit segments same as 32bit ones. I have code to handle 16-bit and 32-bit address encodings differently. Segmentation is used if !user_64bit_mode(regs). In such a case, the emulation code will check the segment descriptor D flag and the address-size overrides prefix to determine the address size and use 16-bit or 32-bit address encodings as applicable. > > > My emulation code should work in this case as it > > will use segmentation in 32-bit code descriptors. Is there anything else > > needed? > If I understand you correctly, you are saying that SLDT > executed in 64bit code segment, will inevitably segfault > to userspace. Correct. > If this is the case and it makes your code > simpler, then its perfectly fine with me as dosemu does > not do this and the 64bit DOS progs are not anticipated. But if 32-bit or 16-bit code segments are used emulation will be used. Thanks and BR, Ricardo