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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id n20-20020a170902d0d400b00192e1590349sm25533566pln.216.2023.01.19.16.44.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 16:44:31 -0800 (PST) Date: Thu, 19 Jan 2023 16:44:30 -0800 From: Kees Cook To: Rick Edgecombe 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 , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H . J . Lu" , Jann Horn , Jonathan Corbet , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , Weijiang Yang , "Kirill A . Shutemov" , John Allen , kcc@google.com, eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com, dethoma@microsoft.com, akpm@linux-foundation.org, Andrew.Cooper3@citrix.com, christina.schimpe@intel.com, Yu-cheng Yu Subject: Re: [PATCH v5 03/39] x86/cpufeatures: Add CPU feature flags for shadow stacks Message-ID: <202301191644.CBF2951@keescook> References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-4-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230119212317.8324-4-rick.p.edgecombe@intel.com> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: c87stwgqmedkmsg74rgtt1hudz7kdngq X-Rspamd-Queue-Id: DAA8A100011 X-HE-Tag: 1674175472-589854 X-HE-Meta: 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 evAVybm8 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 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 Thu, Jan 19, 2023 at 01:22:41PM -0800, Rick Edgecombe wrote: > From: Yu-cheng Yu > > The Control-Flow Enforcement Technology contains two related features, > one of which is Shadow Stacks. Future patches will utilize this feature > for shadow stack support in KVM, so add a CPU feature flags for Shadow > Stacks (CPUID.(EAX=7,ECX=0):ECX[bit 7]). > > To protect shadow stack state from malicious modification, the registers > are only accessible in supervisor mode. This implementation > context-switches the registers with XSAVES. Make X86_FEATURE_SHSTK depend > on XSAVES. > > The shadow stack feature, enumerated by the CPUID bit described above, > encompasses both supervisor and userspace support for shadow stack. In > near future patches, only userspace shadow stack will be enabled. In > expectation of future supervisor shadow stack support, create a software > CPU capability to enumerate kernel utilization of userspace shadow stack > support. This user shadow stack bit should depend on the HW "shstk" > capability and that logic will be implemented in future patches. > > Tested-by: Pengfei Xu > Tested-by: John Allen > Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook -- Kees Cook