From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function Date: Fri, 7 Jun 2019 13:00:01 -0700 Message-ID: <4b448cde-ee4e-1c95-0f7f-4fe694be7db6@intel.com> References: <20190606200926.4029-1-yu-cheng.yu@intel.com> <20190606200926.4029-4-yu-cheng.yu@intel.com> <20190607080832.GT3419@hirez.programming.kicks-ass.net> <20190607174336.GM3436@hirez.programming.kicks-ass.net> <34E0D316-552A-401C-ABAA-5584B5BC98C5@amacapital.net> <7e0b97bf1fbe6ff20653a8e4e147c6285cc5552d.camel@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <7e0b97bf1fbe6ff20653a8e4e147c6285cc5552d.camel@intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Yu-cheng Yu , Andy Lutomirski Cc: Peter Zijlstra , 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 , 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 List-Id: linux-arch.vger.kernel.org On 6/7/19 12:49 PM, Yu-cheng Yu wrote: >> >> This also gives us an excellent opportunity to make it read-only as seen from >> userspace to prevent exploits from just poking it full of ones before >> redirecting execution. > GLIBC sets bits only for legacy code, and then makes the bitmap read-only. That > avoids most issues: > > To populate bitmap pages, mprotect() is required. > Reading zero bitmap pages would not waste more physical memory, right? Huh, how does glibc know about all possible past and future legacy code in the application? From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga05.intel.com ([192.55.52.43]:60464 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728727AbfFGUAD (ORCPT ); Fri, 7 Jun 2019 16:00:03 -0400 Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function References: <20190606200926.4029-1-yu-cheng.yu@intel.com> <20190606200926.4029-4-yu-cheng.yu@intel.com> <20190607080832.GT3419@hirez.programming.kicks-ass.net> <20190607174336.GM3436@hirez.programming.kicks-ass.net> <34E0D316-552A-401C-ABAA-5584B5BC98C5@amacapital.net> <7e0b97bf1fbe6ff20653a8e4e147c6285cc5552d.camel@intel.com> From: Dave Hansen Message-ID: <4b448cde-ee4e-1c95-0f7f-4fe694be7db6@intel.com> Date: Fri, 7 Jun 2019 13:00:01 -0700 MIME-Version: 1.0 In-Reply-To: <7e0b97bf1fbe6ff20653a8e4e147c6285cc5552d.camel@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Yu-cheng Yu , Andy Lutomirski Cc: Peter Zijlstra , 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 , 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 , Pavel Machek , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin Message-ID: <20190607200001.Eiva6fSliox3ORkUhREnn9hm6H4825fJEK0HVMmA5VY@z> On 6/7/19 12:49 PM, Yu-cheng Yu wrote: >> >> This also gives us an excellent opportunity to make it read-only as seen from >> userspace to prevent exploits from just poking it full of ones before >> redirecting execution. > GLIBC sets bits only for legacy code, and then makes the bitmap read-only. That > avoids most issues: > > To populate bitmap pages, mprotect() is required. > Reading zero bitmap pages would not waste more physical memory, right? Huh, how does glibc know about all possible past and future legacy code in the application?