From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection Date: Fri, 06 Mar 2020 13:16:55 -0800 Message-ID: References: <20200205181935.3712-1-yu-cheng.yu@intel.com> <20200205181935.3712-6-yu-cheng.yu@intel.com> <070d9d78981f0aad2baf740233e8dfc32ecd29d7.camel@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-doc-owner@vger.kernel.org To: Dave Hansen , 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 Fri, 2020-03-06 at 11:02 -0800, Dave Hansen wrote: > On 3/6/20 10:37 AM, Yu-cheng Yu wrote: > > We used to do this for CET instructions, but after adding kernel-mode > > instructions and inserting ENDBR's, the code becomes cluttered. I also > > found an earlier discussion on the ENDBR: > > > > https://lore.kernel.org/lkml/CALCETrVRH8LeYoo7V1VBPqg4WS0Enxtizt=T7dPvgoeWfJrdzA@mail.gmail.com/ > > > > It makes sense to let the user know early on that the system cannot support > > CET and cannot build a CET-enabled kernel. > > > > One thing we can do is to disable CET in Kconfig and not in kernel > > build, which I will do in the next version. > > I'll go on the record and say I think we should allow building > CET-enabled kernels on old toolchains. We need it for build test > coverage. We can spit out a warning, but we need to allow building it. The build test will go through (assembler or .byte), once the opcode patch is applied [1]. Also, when we enable kernel-mode CET, it is difficult to build IBT code without the right tool chain. Yu-cheng [1] opcode patch: https://lore.kernel.org/lkml/20200204171425.28073-1-yu-cheng.yu@intel.com/ From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: Subject: Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection From: Yu-cheng Yu Date: Fri, 06 Mar 2020 13:16:55 -0800 In-Reply-To: References: <20200205181935.3712-1-yu-cheng.yu@intel.com> <20200205181935.3712-6-yu-cheng.yu@intel.com> <070d9d78981f0aad2baf740233e8dfc32ecd29d7.camel@intel.com> Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org To: Dave Hansen , 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 , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , x86-patch-review@intel.com List-ID: Message-ID: <20200306211655.USUyRGhN7RIPsRXl6PEc_vDaHqxSqddBjxOsCffozbU@z> On Fri, 2020-03-06 at 11:02 -0800, Dave Hansen wrote: > On 3/6/20 10:37 AM, Yu-cheng Yu wrote: > > We used to do this for CET instructions, but after adding kernel-mode > > instructions and inserting ENDBR's, the code becomes cluttered. I also > > found an earlier discussion on the ENDBR: > > > > https://lore.kernel.org/lkml/CALCETrVRH8LeYoo7V1VBPqg4WS0Enxtizt=T7dPvgoeWfJrdzA@mail.gmail.com/ > > > > It makes sense to let the user know early on that the system cannot support > > CET and cannot build a CET-enabled kernel. > > > > One thing we can do is to disable CET in Kconfig and not in kernel > > build, which I will do in the next version. > > I'll go on the record and say I think we should allow building > CET-enabled kernels on old toolchains. We need it for build test > coverage. We can spit out a warning, but we need to allow building it. The build test will go through (assembler or .byte), once the opcode patch is applied [1]. Also, when we enable kernel-mode CET, it is difficult to build IBT code without the right tool chain. Yu-cheng [1] opcode patch: https://lore.kernel.org/lkml/20200204171425.28073-1-yu-cheng.yu@intel.com/