From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3579EC43465 for ; Fri, 18 Sep 2020 21:21:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 004EA222BB for ; Fri, 18 Sep 2020 21:21:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726252AbgIRVVj (ORCPT ); Fri, 18 Sep 2020 17:21:39 -0400 Received: from mga02.intel.com ([134.134.136.20]:39891 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726247AbgIRVVj (ORCPT ); Fri, 18 Sep 2020 17:21:39 -0400 IronPort-SDR: /YNQjK+3CfGUAwbUQfkGYAZ53dm1qYamVyqqoLDI6HzqIqiodyvlX9vt5N81oy/t1oLXSPX9De BQoZU5nCnUdQ== X-IronPort-AV: E=McAfee;i="6000,8403,9748"; a="147718685" X-IronPort-AV: E=Sophos;i="5.77,274,1596524400"; d="scan'208";a="147718685" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Sep 2020 14:21:24 -0700 IronPort-SDR: cqPmBsZP+6LCDOndU195386/Bgju5YHVNwiypFk5BMbPE9dJG8qo+zu4vjlHNtpOUfjRfXM7d/ s8nIq35e4evA== X-IronPort-AV: E=Sophos;i="5.77,274,1596524400"; d="scan'208";a="381051016" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.212.0.248]) ([10.212.0.248]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Sep 2020 14:21:13 -0700 Subject: Re: [PATCH v12 8/8] x86: Disallow vsyscall emulation when CET is enabled To: Pavel Machek , Dave Hansen Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang References: <20200918192312.25978-1-yu-cheng.yu@intel.com> <20200918192312.25978-9-yu-cheng.yu@intel.com> <20200918210026.GC4304@duo.ucw.cz> From: "Yu, Yu-cheng" Message-ID: <862eef02-eba2-e13f-ed67-f915f749ebca@intel.com> Date: Fri, 18 Sep 2020 14:21:10 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200918210026.GC4304@duo.ucw.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On 9/18/2020 2:00 PM, Pavel Machek wrote: > On Fri 2020-09-18 12:32:57, Dave Hansen wrote: >> On 9/18/20 12:23 PM, Yu-cheng Yu wrote: >>> Emulation of the legacy vsyscall page is required by some programs >>> built before 2013. Newer programs after 2013 don't use it. >>> Disable vsyscall emulation when Control-flow Enforcement (CET) is >>> enabled to enhance security. >> >> How does this "enhance security"? >> >> What is the connection between vsyscall emulation and CET? > > Boom. > > We don't break compatibility by default, and you should not tell > people to enable CET by default if you plan to do this. I would revise the wording if there is another version. What this patch does is: If an application is compiled for CET and the system supports it, then the application cannot do vsyscall emulation. Earlier we allow the emulation, and had a patch that fixes the shadow stack and endbr for the emulation code. Since newer programs mostly do no do the emulation, we changed the patch do block it when attempted. This patch would not block any legacy applications or any applications on older machines. Yu-cheng