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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 11sm7480618pgz.22.2021.02.04.12.22.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Feb 2021 12:22:14 -0800 (PST) Date: Thu, 4 Feb 2021 12:22:13 -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 14/25] x86/mm: Update maybe_mkwrite() for shadow stack Message-ID: <202102041222.B111A20A9@keescook> References: <20210203225547.32221-1-yu-cheng.yu@intel.com> <20210203225547.32221-15-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210203225547.32221-15-yu-cheng.yu@intel.com> 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 Wed, Feb 03, 2021 at 02:55:36PM -0800, Yu-cheng Yu wrote: > When serving a page fault, maybe_mkwrite() makes a PTE writable if its vma > has VM_WRITE. > > A shadow stack vma has VM_SHSTK. Its PTEs have _PAGE_DIRTY, but not > _PAGE_WRITE. In fork(), _PAGE_DIRTY is cleared to effect copy-on-write, > and in page fault, _PAGE_DIRTY is restored and the shadow stack page is > writable again. > > Update maybe_mkwrite() by introducing arch_maybe_mkwrite(), which sets > _PAGE_DIRTY for a shadow stack PTE. > > Apply the same changes to maybe_pmd_mkwrite(). > > Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook -- Kees Cook