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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id ju2-20020a170903428200b00174d9bbeda4sm6187424plb.197.2022.12.02.18.22.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Dec 2022 18:22:07 -0800 (PST) Date: Fri, 2 Dec 2022 18:22:06 -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 v4 03/39] x86/cpufeatures: Add CPU feature flags for shadow stacks Message-ID: <202212021822.79D8BD1@keescook> References: <20221203003606.6838-1-rick.p.edgecombe@intel.com> <20221203003606.6838-4-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221203003606.6838-4-rick.p.edgecombe@intel.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 19EBDC0016 X-Rspam-User: X-Stat-Signature: kg59u18f8tjzm33ns5nn58otfxdqz5oi X-Spamd-Result: default: False [5.08 / 9.00]; SORBS_IRL_BL(3.00)[209.85.214.179:from]; SUSPICIOUS_RECIPS(1.50)[]; MID_RHS_NOT_FQDN(0.50)[]; RCVD_NO_TLS_LAST(0.10)[]; MIME_GOOD(-0.10)[text/plain]; BAD_REP_POLICIES(0.10)[]; BAYES_HAM(-0.02)[47.72%]; DKIM_TRACE(0.00)[chromium.org:+]; RCPT_COUNT_TWELVE(0.00)[39]; FROM_EQ_ENVFROM(0.00)[]; DMARC_POLICY_ALLOW(0.00)[chromium.org,none]; MIME_TRACE(0.00)[0:+]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_COUNT_THREE(0.00)[3]; PREVIOUSLY_DELIVERED(0.00)[linux-mm@kvack.org]; R_DKIM_ALLOW(0.00)[chromium.org:s=google]; ARC_NA(0.00)[]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; FROM_HAS_DN(0.00)[]; R_SPF_ALLOW(0.00)[+ip4:209.85.128.0/17]; TO_DN_SOME(0.00)[]; TAGGED_RCPT(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[] X-HE-Tag: 1670034128-835945 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 Fri, Dec 02, 2022 at 04:35:30PM -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 will also allow for userspace shadow stack to be disabled, > while leaving the shadow stack hardware capability exposed in the cpuinfo > proc. 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