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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id e8-20020aa79808000000b005897f5436c0sm19809081pfl.118.2023.01.19.17.05.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 17:05:58 -0800 (PST) Date: Thu, 19 Jan 2023 17:05:57 -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 29/39] x86/shstk: Introduce routines modifying shstk Message-ID: <202301191705.9D4E6EA@keescook> References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-30-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230119212317.8324-30-rick.p.edgecombe@intel.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: E183BA0004 X-Stat-Signature: ubshooepjgbrccudg63z48z8ga57s7ih X-HE-Tag: 1674176759-936002 X-HE-Meta: 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 fMEA+u/z Zvb5Tf/8/i3R7xm15gf3DpMQ9spHEqZ0Nh2jR3NBQfT1KaXKefD17aNqIDt5MnHFoGEdpCJapLI8/PB8GC/pR2N6KbO7ksVVLm+jf5fE/WgAgNqhVkUQoV7YaW5ApI2ACtROfjmqTMySKT8HhY9is43mSx0RYXRAsxM3ndYBuuKlq6OVxqSVzK1vwOAFMsIYGCMgGKDXac1hna60K1J0l07ocMS08rAk/YT0mk+NEv1ZIfPL4wLfBZZU7sDmj4sAAIJSLXeEgdiT0IoUFTyTeD3XjBwbkNKUiOR5/gablNznt2DCXKHhqsGbE4sGqkspzm5V41S53VAYvRrS1N5EOMaGQBqI8qx2jG3WVZhNCM9fiFUb0eVJV6p8+AByMWkryJLxhd7rKVKGJS3E5e43nmhf2dLvAj0KFiN6CO8LpwE/vn77SvWsvMIF6VdpofDSUt6uE3HDmOz+yGb4FK73u3dOo9WSepdcipOM/C/poVv2c7SDSQT7P1PfvLAgxa0Bv7UuhjrwLopAcuzIrSADqfe+hFAlAMi9j2UcBR2RbTYAgpSY= 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 01:23:07PM -0800, Rick Edgecombe wrote: > From: Yu-cheng Yu > > Shadow stacks are normally written to via CALL/RET or specific CET > instructions like RSTORSSP/SAVEPREVSSP. However during some Linux > operations the kernel will need to write to directly using the ring-0 only > WRUSS instruction. > > A shadow stack restore token marks a restore point of the shadow stack, and > the address in a token must point directly above the token, which is within > the same shadow stack. This is distinctively different from other pointers > on the shadow stack, since those pointers point to executable code area. > > Introduce token setup and verify routines. Also introduce WRUSS, which is > a kernel-mode instruction but writes directly to user shadow stack. > > In future patches that enable shadow stack to work with signals, the kernel > will need something to denote the point in the stack where sigreturn may be > called. This will prevent attackers calling sigreturn at arbitrary places > in the stack, in order to help prevent SROP attacks. > > To do this, something that can only be written by the kernel needs to be > placed on the shadow stack. This can be accomplished by setting bit 63 in > the frame written to the shadow stack. Userspace return addresses can't > have this bit set as it is in the kernel range. It is also can't be a > valid restore token. > > Tested-by: Pengfei Xu > Tested-by: John Allen > Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook -- Kees Cook