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[34.168.202.30]) by smtp.gmail.com with ESMTPSA id 62-20020a621441000000b00575bab45644sm3343019pfu.61.2022.12.06.07.02.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Dec 2022 07:02:54 -0800 (PST) From: jeffxu@chromium.org To: skhan@linuxfoundation.org, keescook@chromium.org Cc: 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, Jeff Xu Subject: [PATCH v4 4/6] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd Date: Tue, 6 Dec 2022 15:02:31 +0000 Message-Id: <20221206150233.1963717-5-jeffxu@google.com> X-Mailer: git-send-email 2.39.0.rc0.267.gcb52ba06e7-goog In-Reply-To: <20221206150233.1963717-1-jeffxu@google.com> References: <20221206150233.1963717-1-jeffxu@google.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1751477845282088320?= X-GMAIL-MSGID: =?utf-8?q?1751477845282088320?= 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 won't be able to modify the content of the memfd. Typically, application seals the memfd right after writing to it. For example: 3> shall be right after 2> in steps below. 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 --- mm/memfd.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/memfd.c b/mm/memfd.c index ec70675a7069..92f0a5765f7c 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -222,6 +222,12 @@ static int memfd_add_seals(struct file *file, unsigned int seals) } } + /* + * SEAL_EXEC implys SEAL_WRITE, making W^X from the start. + */ + if (seals & F_SEAL_EXEC && inode->i_mode & 0111) + seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE; + *file_seals |= seals; error = 0;