From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function Date: Mon, 10 Jun 2019 08:47:45 -0700 Message-ID: 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> <20190608205218.GA2359@xo-6d-61-c0.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190608205218.GA2359@xo-6d-61-c0.localdomain> Sender: linux-kernel-owner@vger.kernel.org To: Pavel Machek , Dave Hansen 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 , 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 List-Id: linux-arch.vger.kernel.org On Sat, 2019-06-08 at 22:52 +0200, Pavel Machek wrote: > Hi! > > > > I've no idea what the kernel should do; since you failed to answer the > > > question what happens when you point this to garbage. > > > > > > Does it then fault or what? > > > > Yeah, I think you'll fault with a rather mysterious CR2 value since > > you'll go look at the instruction that faulted and not see any > > references to the CR2 value. > > > > I think this new MSR probably needs to get included in oops output when > > CET is enabled. > > > > Why don't we require that a VMA be in place for the entire bitmap? > > Don't we need a "get" prctl function too in case something like a JIT is > > running and needs to find the location of this bitmap to set bits itself? > > > > Or, do we just go whole-hog and have the kernel manage the bitmap > > itself. Our interface here could be: > > > > prctl(PR_MARK_CODE_AS_LEGACY, start, size); > > > > and then have the kernel allocate and set the bitmap for those code > > locations. > > For the record, that sounds like a better interface than userspace knowing > about the bitmap formats... > Pavel Initially we implemented the bitmap that way. To manage the bitmap, every time the application issues a syscall for a .so it loads, and the kernel does copy_from_user() & copy_to_user() (or similar things). If a system has a few legacy .so files and every application does the same, it can take a long time to boot up. Yu-cheng From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga12.intel.com ([192.55.52.136]:5731 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2403791AbfFJPzx (ORCPT ); Mon, 10 Jun 2019 11:55:53 -0400 Message-ID: Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function From: Yu-cheng Yu Date: Mon, 10 Jun 2019 08:47:45 -0700 In-Reply-To: <20190608205218.GA2359@xo-6d-61-c0.localdomain> 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> <20190608205218.GA2359@xo-6d-61-c0.localdomain> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Pavel Machek , Dave Hansen 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 , 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 , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin Message-ID: <20190610154745.rqgQN1ZkLubSvR9XSzKj875R0hdMpf89Klk9ytGsw8Q@z> On Sat, 2019-06-08 at 22:52 +0200, Pavel Machek wrote: > Hi! > > > > I've no idea what the kernel should do; since you failed to answer the > > > question what happens when you point this to garbage. > > > > > > Does it then fault or what? > > > > Yeah, I think you'll fault with a rather mysterious CR2 value since > > you'll go look at the instruction that faulted and not see any > > references to the CR2 value. > > > > I think this new MSR probably needs to get included in oops output when > > CET is enabled. > > > > Why don't we require that a VMA be in place for the entire bitmap? > > Don't we need a "get" prctl function too in case something like a JIT is > > running and needs to find the location of this bitmap to set bits itself? > > > > Or, do we just go whole-hog and have the kernel manage the bitmap > > itself. Our interface here could be: > > > > prctl(PR_MARK_CODE_AS_LEGACY, start, size); > > > > and then have the kernel allocate and set the bitmap for those code > > locations. > > For the record, that sounds like a better interface than userspace knowing > about the bitmap formats... > Pavel Initially we implemented the bitmap that way. To manage the bitmap, every time the application issues a syscall for a .so it loads, and the kernel does copy_from_user() & copy_to_user() (or similar things). If a system has a few legacy .so files and every application does the same, it can take a long time to boot up. Yu-cheng