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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id u11-20020a6540cb000000b0046ff3634a78sm21576083pgp.71.2023.01.19.16.57.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 16:57:24 -0800 (PST) Date: Thu, 19 Jan 2023 16:57:23 -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 11/39] x86/mm: Update pte_modify for _PAGE_COW Message-ID: <202301191657.3B81D1C589@keescook> References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-12-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230119212317.8324-12-rick.p.edgecombe@intel.com> X-Rspamd-Queue-Id: 2E907140011 X-Stat-Signature: ukh814kf76b6qmpo3fwyq649x6gbp4cy X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674176246-595684 X-HE-Meta: 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 LXfiydnS 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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 01:22:49PM -0800, Rick Edgecombe wrote: > From: Yu-cheng Yu > > The Write=0,Dirty=1 PTE has been used to indicate copy-on-write pages. > However, newer x86 processors also regard a Write=0,Dirty=1 PTE as a > shadow stack page. In order to separate the two, the software-defined > _PAGE_DIRTY is changed to _PAGE_COW for the copy-on-write case, and > pte_*() are updated to do this. > > pte_modify() takes a "raw" pgprot_t which was not necessarily created > with any of the existing PTE bit helpers. That means that it can return a > pte_t with Write=0,Dirty=1, a shadow stack PTE, when it did not intend to > create one. > > However pte_modify() changes a PTE to 'newprot', but it doesn't use the > pte_*(). Modify it to also move _PAGE_DIRTY to _PAGE_COW. Do this by > using the pte_mkdirty() helper. Since pte_mkdirty() also sets the soft > dirty bit, extract a helper that optionally doesn't set > _PAGE_SOFT_DIRTY. This helper will allow future logic for deciding when to > move _PAGE_DIRTY to _PAGE_COW can live in one place. > > Apply the same changes to pmd_modify(). > > Tested-by: Pengfei Xu > Tested-by: John Allen > Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook -- Kees Cook