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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id e12sm6152391pjj.23.2021.02.04.11.59.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Feb 2021 11:59:44 -0800 (PST) Date: Thu, 4 Feb 2021 11:59:43 -0800 From: Kees Cook To: Yu-cheng Yu 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 , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu Subject: Re: [PATCH v19 05/25] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Message-ID: <202102041159.44C6C3588@keescook> References: <20210203225547.32221-1-yu-cheng.yu@intel.com> <20210203225547.32221-6-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210203225547.32221-6-yu-cheng.yu@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Feb 03, 2021 at 02:55:27PM -0800, Yu-cheng Yu wrote: > Control-flow Enforcement Technology (CET) introduces these MSRs: > > MSR_IA32_U_CET (user-mode CET settings), > MSR_IA32_PL3_SSP (user-mode shadow stack pointer), > > MSR_IA32_PL0_SSP (kernel-mode shadow stack pointer), > MSR_IA32_PL1_SSP (Privilege Level 1 shadow stack pointer), > MSR_IA32_PL2_SSP (Privilege Level 2 shadow stack pointer), > MSR_IA32_S_CET (kernel-mode CET settings), > MSR_IA32_INT_SSP_TAB (exception shadow stack table). > > The two user-mode MSRs belong to XFEATURE_CET_USER. The first three of > kernel-mode MSRs belong to XFEATURE_CET_KERNEL. Both XSAVES states are > supervisor states. This means that there is no direct, unprivileged access > to these states, making it harder for an attacker to subvert CET. > > For sigreturn and future ptrace() support, shadow stack address and MSR > reserved bits are checked before written to the supervisor states. > > Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook -- Kees Cook