Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754597AbdCHWnD (ORCPT ); Wed, 8 Mar 2017 17:43:03 -0500 Received: from mail-ua0-f181.google.com ([209.85.217.181]:34442 "EHLO mail-ua0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751262AbdCHWnA (ORCPT ); Wed, 8 Mar 2017 17:43:00 -0500 MIME-Version: 1.0 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> From: Andy Lutomirski Date: Wed, 8 Mar 2017 08:06:23 -0800 Message-ID: Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention To: Stas Sergeev Cc: Ricardo Neri , 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 ML , linux-msdos@vger.kernel.org, wine-devel@winehq.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v28MhrjP013598 Content-Length: 1987 Lines: 54 On Wed, Mar 8, 2017 at 6:08 AM, 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. Can you remind me what was special about it? It looks like you still emulate them in v8086 mode. > > 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? > 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. What I'd actually like to see is a totally separate patchset that adds an inheritable (but reset on exec) per-task mask of legacy compatibility features to disable. Maybe: sys_adjust_compat_mask(int op, int word, u32 mask); op could indicate that we want to so SET, OR, AND, or READ. word would be 0 for now. It could be a prctl, too. Things in the mask could include: COMPAT_MASK0_X86_64_VSYSCALL [1] COMPAT_MASK0_X86_UMIP_FIXUP I'm sure I could think of more along these lines. Then DOSEMU (and future WINE versions, too) could just mask off X86_UMIP_FIXUP and do their own emulation [1] For those of you thinking about this and realizing that VSYSCALL readability is inherently global and not per-task, I know how to fix that for essentially no cost :) --Andy