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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 129-20020a621987000000b0056262811c5fsm15535730pfz.59.2022.12.08.08.27.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Dec 2022 08:27:51 -0800 (PST) Date: Thu, 8 Dec 2022 08:27:50 -0800 From: Kees Cook To: jeffxu@chromium.org Cc: skhan@linuxfoundation.org, akpm@linux-foundation.org, dmitry.torokhov@gmail.com, dverkamp@chromium.org, hughd@google.com, jeffxu@google.com, jorgelo@chromium.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, jannh@google.com, linux-hardening@vger.kernel.org Subject: Re: [PATCH v6 4/6] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd Message-ID: <202212080827.41F083F@keescook> References: <20221207154939.2532830-1-jeffxu@google.com> <20221207154939.2532830-5-jeffxu@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221207154939.2532830-5-jeffxu@google.com> X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 43F5640019 X-Stat-Signature: 6h6yarux54uafq45kas5k7ihmpsoywru X-HE-Tag: 1670516873-433931 X-HE-Meta: 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 /SOvQ6Fj AfLz3Q69g/t5cWp/YjqROVa3uGIor5B07Vs2ephlr1zP3qMz9ScjoApDSpBRgftqkf/vkML5OSnn+viVxDqPsIoXSm6yksORckKarpmD6Rr9/8nxyIno2JXuGLOi3SFAZ7BsDQ8aqjw0/+SVe1hQssw9QXSmDWFmBffABnS7n+HEZP48b2e7gXP30qswjzBvFr7ArdojhtK6JMn13ajv+qlRJ0g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000600, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Dec 07, 2022 at 03:49:37PM +0000, jeffxu@chromium.org wrote: > From: Jeff Xu > > In order to avoid WX mappings, add F_SEAL_WRITE when apply > F_SEAL_EXEC to an executable memfd, so W^X from start. > > This implys application need to fill the content of the memfd first, > after F_SEAL_EXEC is applied, application can no longer modify the > content of the memfd. > > Typically, application seals the memfd right after writing to it. > For example: > 1. memfd_create(MFD_EXEC). > 2. write() code to the memfd. > 3. fcntl(F_ADD_SEALS, F_SEAL_EXEC) to convert the memfd to W^X. > 4. call exec() on the memfd. > > Signed-off-by: Jeff Xu Reviewed-by: Kees Cook -- Kees Cook