From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933967AbdCJViA (ORCPT ); Fri, 10 Mar 2017 16:38:00 -0500 Received: from smtp53.i.mail.ru ([94.100.177.113]:53822 "EHLO smtp53.i.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933374AbdCJVhz (ORCPT ); Fri, 10 Mar 2017 16:37:55 -0500 Subject: Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention To: Andy Lutomirski References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <79ba0fff-4c01-2bfa-06cb-5cfc98dd710c@list.ru> <997ba581-ecfa-b773-a48e-85b92a439836@list.ru> <1489021909.131264.30.camel@ranerica-desktop> <7ea39103-c193-4d6d-572f-a1bdb27c3627@list.ru> Cc: Andy Lutomirski , Ricardo Neri , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , 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 , 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 From: Stas Sergeev Message-ID: Date: Sat, 11 Mar 2017 00:37:19 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Authentication-Results: smtp53.i.mail.ru; auth=pass smtp.auth=stsp@list.ru smtp.mailfrom=stsp@list.ru X-7FA49CB5: 0D63561A33F958A5B2E947903D244843D00CD781CF6DD4FC06B4877B0A18B3129F18ECD7E95F35E929AFE063DF4C541CF072BA2BDBD9BA9FE09B49CFA3B028330BF2EBBBDD9D6B0FAEAACC865B01FC22 X-Mailru-Sender: F1845AB6CCC9920DF7838D61D4D05C425A762709B64DF71696DC40CD114B537674FF3E26B2C895931653177920737CA72999BEE114A20FF4278B2D54D4112F244F0A872F021F905956A8FB0C6EBA5FCCEAB4BC95F72C04283CDA0F3B3F5B9367 X-Mras: OK Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 11.03.2017 00:04, Andy Lutomirski пишет: > On Fri, Mar 10, 2017 at 2:30 AM, Stas Sergeev wrote: >> 10.03.2017 05:41, Andy Lutomirski пишет: >> >>> On Wed, Mar 8, 2017 at 5:11 PM, Ricardo Neri >>> wrote: >>>> On Wed, 2017-03-08 at 19:53 +0300, Stas Sergeev wrote: >>>>> 08.03.2017 19:46, Andy Lutomirski пишет: >>>>>>> No no, since I meant prot mode, this is not what I need. >>>>>>> I would never need to disable UMIP as to allow the >>>>>>> prot mode apps to do SLDT. Instead it would be good >>>>>>> to have an ability to provide a replacement for the dummy >>>>>>> emulation that is currently being proposed for kernel. >>>>>>> All is needed for this, is just to deliver a SIGSEGV. >>>>>> That's what I meant. Turning off FIXUP_UMIP would leave UMIP on but >>>>>> turn off the fixup, so you'd get a SIGSEGV indicating #GP (or a vm86 >>>>>> GP exit). >>>>> But then I am confused with the word "compat" in >>>>> your "COMPAT_MASK0_X86_UMIP_FIXUP" and >>>>> "sys_adjust_compat_mask(int op, int word, u32 mask);" >>>>> >>>>> Leaving UMIP on and only disabling a fixup doesn't >>>>> sound like a compat option to me. I would expect >>>>> compat to disable it completely. >>>> I guess that the _UMIP_FIXUP part makes it clear that emulation, not >>>> UMIP is disabled, allowing the SIGSEGV be delivered to the user space >>>> program. >>>> >>>> Would having a COMPAT_MASK0_X86_UMIP_FIXUP to disable emulation and a >>>> COMPAT_MASK0_X86_UMIP to disable UMIP make sense? >>>> >>>> Also, wouldn't having a COMPAT_MASK0_X86_UMIP to disable UMIP defeat its >>>> purpose? Applications could simply use this compat mask to bypass UMIP >>>> and gain access to the instructions it protects. >>>> >>> I was obviously extremely unclear. The point of the proposed syscall >>> is to let programs opt out of legacy features. >> I guess both "compat" and "legacy" are misleading >> here. Maybe these are "x86-specific" or "hypervisor-specific", >> but a mere enabling of UMIP doesn't immediately make >> the use of SLDT instruction a legacy IMHO. > Sure it is. :) Using SLDT from user mode is a legacy ability that > just happens to still work on existing CPUs and kernels. Once UMIP > goes in, it will officially be obsolete Yes, but the names you suggest, imply that "UMIP_FIXUP" is legacy or compat, which I find misleading because it have just appeared. Maybe something like "COMPAT_X86_UMIP_INSNS_EMU"?