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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id c194-20020a621ccb000000b0056d3b8f530csm5759664pfc.34.2022.12.02.18.52.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Dec 2022 18:52:33 -0800 (PST) Date: Fri, 2 Dec 2022 18:52:32 -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 Subject: Re: [PATCH v4 31/39] x86/shstk: Support wrss for userspace Message-ID: <202212021852.88C57CF544@keescook> References: <20221203003606.6838-1-rick.p.edgecombe@intel.com> <20221203003606.6838-32-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221203003606.6838-32-rick.p.edgecombe@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Fri, Dec 02, 2022 at 04:35:58PM -0800, Rick Edgecombe wrote: > For the current shadow stack implementation, shadow stacks contents can't > easily be provisioned with arbitrary data. This property helps apps > protect themselves better, but also restricts any potential apps that may > want to do exotic things at the expense of a little security. > > The x86 shadow stack feature introduces a new instruction, wrss, which > can be enabled to write directly to shadow stack permissioned memory from > userspace. Allow it to get enabled via the prctl interface. > > Only enable the userspace wrss instruction, which allows writes to > userspace shadow stacks from userspace. Do not allow it to be enabled > independently of shadow stack, as HW does not support using WRSS when > shadow stack is disabled. > > From a fault handler perspective, WRSS will behave very similar to WRUSS, > which is treated like a user access from a #PF err code perspective. > > Tested-by: Pengfei Xu > Tested-by: John Allen > Signed-off-by: Rick Edgecombe Reviewed-by: Kees Cook -- Kees Cook