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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id u12-20020a17090341cc00b001888cadf8f6sm7038231ple.49.2023.01.19.16.47.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 16:47:34 -0800 (PST) Date: Thu, 19 Jan 2023 16:47:34 -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 v5 06/39] x86/fpu: Add helper for modifying xstate Message-ID: <202301191647.0F4AB4B525@keescook> References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-7-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230119212317.8324-7-rick.p.edgecombe@intel.com> X-Rspamd-Queue-Id: 573E4180011 X-Stat-Signature: k7bwdcpxp4ifnjrpierqmh33jntjf5pw X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674175656-678356 X-HE-Meta: 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 hwVskKhW 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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 01:22:44PM -0800, Rick Edgecombe wrote: > Just like user xfeatures, supervisor xfeatures can be active in the > registers or present in the task FPU buffer. If the registers are > active, the registers can be modified directly. If the registers are > not active, the modification must be performed on the task FPU buffer. > > When the state is not active, the kernel could perform modifications > directly to the buffer. But in order for it to do that, it needs > to know where in the buffer the specific state it wants to modify is > located. Doing this is not robust against optimizations that compact > the FPU buffer, as each access would require computing where in the > buffer it is. > > The easiest way to modify supervisor xfeature data is to force restore > the registers and write directly to the MSRs. Often times this is just fine > anyway as the registers need to be restored before returning to userspace. > Do this for now, leaving buffer writing optimizations for the future. > > Add a new function fpregs_lock_and_load() that can simultaneously call > fpregs_lock() and do this restore. Also perform some extra sanity > checks in this function since this will be used in non-fpu focused code. > > Tested-by: Pengfei Xu > Tested-by: John Allen > Suggested-by: Thomas Gleixner > Signed-off-by: Rick Edgecombe Reviewed-by: Kees Cook -- Kees Cook