From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from changing shadow stack Date: Wed, 11 Jul 2018 09:22:28 -0700 Message-ID: References: <20180710222639.8241-1-yu-cheng.yu@intel.com> <20180710222639.8241-16-yu-cheng.yu@intel.com> <04800c52-1f86-c485-ba7c-2216d8c4966f@linux.intel.com> <20180711091232.GU2476@hirez.programming.kicks-ass.net> <1531325272.13297.27.camel@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <1531325272.13297.27.camel@intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Yu-cheng Yu , Peter Zijlstra 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 , Cyrill Gorcunov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , "Ravi V. Shankar" , Vedvyas List-Id: linux-arch.vger.kernel.org On 07/11/2018 09:07 AM, Yu-cheng Yu wrote: >> Why do we need to disallow this? AFAICT the worst that can happen is >> that a process wrecks itself, so what? > Agree.  I will remove the patch. No so quick. :) We still need to find out a way to handle things that ask for an mprotect() which is incompatible with shadow stacks. PROT_READ without PROT_WRITE comes to mind. We also need to be careful that we don't copy-on-write/copy-on-access pages which fault on PROT_NONE. I *think* it'll get done correctly but we have to be sure. BTW, where are all the selftests for this code? We're slowly building up a list of pathological things that need to get tested. I don't think this can or should get merged before we have selftests. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga02.intel.com ([134.134.136.20]:51815 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732562AbeGKQ1e (ORCPT ); Wed, 11 Jul 2018 12:27:34 -0400 Subject: Re: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from changing shadow stack References: <20180710222639.8241-1-yu-cheng.yu@intel.com> <20180710222639.8241-16-yu-cheng.yu@intel.com> <04800c52-1f86-c485-ba7c-2216d8c4966f@linux.intel.com> <20180711091232.GU2476@hirez.programming.kicks-ass.net> <1531325272.13297.27.camel@intel.com> From: Dave Hansen Message-ID: Date: Wed, 11 Jul 2018 09:22:28 -0700 MIME-Version: 1.0 In-Reply-To: <1531325272.13297.27.camel@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Yu-cheng Yu , Peter Zijlstra 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 , Cyrill Gorcunov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , "Ravi V. Shankar" , Vedvyas Shanbhogue Message-ID: <20180711162228.XvexMuzstxlGa9jRbDnlGDMrp2Zx8qiod9Qp5OT7dp0@z> On 07/11/2018 09:07 AM, Yu-cheng Yu wrote: >> Why do we need to disallow this? AFAICT the worst that can happen is >> that a process wrecks itself, so what? > Agree.  I will remove the patch. No so quick. :) We still need to find out a way to handle things that ask for an mprotect() which is incompatible with shadow stacks. PROT_READ without PROT_WRITE comes to mind. We also need to be careful that we don't copy-on-write/copy-on-access pages which fault on PROT_NONE. I *think* it'll get done correctly but we have to be sure. BTW, where are all the selftests for this code? We're slowly building up a list of pathological things that need to get tested. I don't think this can or should get merged before we have selftests.