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Lu" Date: Wed, 26 Feb 2020 17:02:28 -0800 Message-ID: Subject: Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection To: Dave Hansen Cc: Yu-cheng Yu , "the arch/x86 maintainers" , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , 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 Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 26, 2020 at 10:05 AM Dave Hansen wrote: > > On 2/5/20 10:19 AM, Yu-cheng Yu wrote: > > +# Check assembler Shadow Stack suppot > > ^ support > > > +ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER > > + ifeq ($(call as-instr, saveprevssp, y),) > > + $(error CONFIG_X86_INTEL_SHADOW_STACK_USER not supported by the assembler) > > + endif > > +endif > > Is this *just* looking for instruction support in the assembler? > > We usually just .byte them, like this for pkeys: > > asm volatile(".byte 0x0f,0x01,0xee\n\t" > : "=a" (pkru), "=d" (edx) > : "c" (ecx)); > > That way everybody with old toolchains can still build the kernel (and > run/test code with your config option on, btw...). CET requires a complete new OS image from kernel, toolchain, run-time. CET enabled kernel without the rest of updated OS won't give you CET at all. -- H.J.