From nobody Thu Sep 18 10:13:43 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94DE1C352A1 for ; Wed, 7 Dec 2022 15:50:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229932AbiLGPuO (ORCPT ); Wed, 7 Dec 2022 10:50:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229828AbiLGPtt (ORCPT ); Wed, 7 Dec 2022 10:49:49 -0500 Received: from mail-pl1-x631.google.com (mail-pl1-x631.google.com [IPv6:2607:f8b0:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0BC6C326DF for ; Wed, 7 Dec 2022 07:49:49 -0800 (PST) Received: by mail-pl1-x631.google.com with SMTP id s7so17386578plk.5 for ; Wed, 07 Dec 2022 07:49:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=68tZIB+0aYpPIylSIqK6cc/meXXHAi0u5AcBKUyeGcY=; b=Pgcz8EqFIllSIrbiyT8+zFROC9GpuYiPrYWAWuws/ZAml4A7Ugasa59H8dzt4twoB4 O0cAxxO9Mke403E/Mj+rjoT+GeN92NHh57bpsegW33gdWlb7tQAmt+ewJoJYOEJvEyeH jGBefsgqUB3ZHzuky+3uRwszEnFjlO/ZS+68A= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=68tZIB+0aYpPIylSIqK6cc/meXXHAi0u5AcBKUyeGcY=; b=c+56RN1229YtQJ1AO9WUr8K7/1VI24Sfek6I1/Ec+Ny4zTwpDaJRcer35OaOO6gv8s lflXc6juRLtA5RzFRGFAmWHG1hxgXvQUFg2Ol5TD/BC4WqBEsEbqNcQzBn6HB+UNjLI8 upDeWUCbu/yb2zPMgiPySR3yflYxRwQjtYe5M+t17Pzgw8hJvHT9bHOAcE0Qyd2mEKxf 8ARWpd2oYr+GgMGb7+7dnDz2o9rLK4Vf1xrKLIPEFNCVyEl3bmx0rK51DvkDqCbX9Btu 67noElESMiyiCC7793QsB8cSBmSvWePmOQXRQLIgJ+FuPAvUmM1bryap78B71DY59rBw ecrA== X-Gm-Message-State: ANoB5plXP6cjVAkEP167xdP2Lm5rEh15OKKTBHV+VrTpW2Goe8pYqJVT f78DnGRTVK/VWi1qo98N52lwZQ== X-Google-Smtp-Source: AA0mqf6RkUVGcJjeQXvXQRSUZJARW3Rj32QYHY9STgcjYfWrJ0sPoKsrx/6HB7CijCJ1h5EjJkg5dg== X-Received: by 2002:a05:6a21:9991:b0:a4:5f8d:805a with SMTP id ve17-20020a056a21999100b000a45f8d805amr1331414pzb.53.1670428188610; Wed, 07 Dec 2022 07:49:48 -0800 (PST) Received: from jeffxud.c.googlers.com.com (30.202.168.34.bc.googleusercontent.com. [34.168.202.30]) by smtp.gmail.com with ESMTPSA id a9-20020a170902ecc900b0017f7628cbddsm14920934plh.30.2022.12.07.07.49.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Dec 2022 07:49:47 -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 Subject: [PATCH v6 4/6] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd Date: Wed, 7 Dec 2022 15:49:37 +0000 Message-Id: <20221207154939.2532830-5-jeffxu@google.com> X-Mailer: git-send-email 2.39.0.rc0.267.gcb52ba06e7-goog In-Reply-To: <20221207154939.2532830-1-jeffxu@google.com> References: <20221207154939.2532830-1-jeffxu@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 --- 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) } } =20 + /* + * SEAL_EXEC implys SEAL_WRITE, making W^X from the start. + */ + if (seals & F_SEAL_EXEC && inode->i_mode & 0111) + seals |=3D F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE; + *file_seals |=3D seals; error =3D 0; =20 --=20 2.39.0.rc0.267.gcb52ba06e7-goog