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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id j18-20020a635952000000b004cd1f1a14f6sm7519083pgm.86.2023.01.19.17.08.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 17:08:04 -0800 (PST) Date: Thu, 19 Jan 2023 17:08:04 -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 37/39] x86: Add PTRACE interface for shadow stack Message-ID: <202301191708.F1C43C9D8@keescook> References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-38-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230119212317.8324-38-rick.p.edgecombe@intel.com> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 49A501C0002 X-Stat-Signature: 41eb5u53xnydsidxn5diec6a1iuo3emt X-HE-Tag: 1674176886-918196 X-HE-Meta: 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 14T+UZDP 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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 01:23:15PM -0800, Rick Edgecombe wrote: > From: Yu-cheng Yu > > Some applications (like GDB) would like to tweak shadow stack state via > ptrace. This allows for existing functionality to continue to work for > seized shadow stack applications. Provide an regset interface for > manipulating the shadow stack pointer (SSP). > > There is already ptrace functionality for accessing xstate, but this > does not include supervisor xfeatures. So there is not a completely > clear place for where to put the shadow stack state. Adding it to the > user xfeatures regset would complicate that code, as it currently shares > logic with signals which should not have supervisor features. > > Don't add a general supervisor xfeature regset like the user one, > because it is better to maintain flexibility for other supervisor > xfeatures to define their own interface. For example, an xfeature may > decide not to expose all of it's state to userspace, as is actually the > case for shadow stack ptrace functionality. A lot of enum values remain > to be used, so just put it in dedicated shadow stack regset. > > The only downside to not having a generic supervisor xfeature regset, > is that apps need to be enlightened of any new supervisor xfeature > exposed this way (i.e. they can't try to have generic save/restore > logic). But maybe that is a good thing, because they have to think > through each new xfeature instead of encountering issues when new a new > supervisor xfeature was added. > > By adding a shadow stack regset, it also has the effect of including the > shadow stack state in a core dump, which could be useful for debugging. > > The shadow stack specific xstate includes the SSP, and the shadow stack > and WRSS enablement status. Enabling shadow stack or wrss in the kernel > involves more than just flipping the bit. The kernel is made aware that > it has to do extra things when cloning or handling signals. That logic > is triggered off of separate feature enablement state kept in the task > struct. So the flipping on HW shadow stack enforcement without notifying > the kernel to change its behavior would severely limit what an application > could do without crashing, and the results would depend on kernel > internal implementation details. There is also no known use for controlling > this state via prtace today. So only expose the SSP, which is something > that userspace already has indirect control over. > > Tested-by: Pengfei Xu > Tested-by: John Allen > Co-developed-by: Rick Edgecombe > Signed-off-by: Rick Edgecombe Reviewed-by: Kees Cook -- Kees Cook