From nobody Thu Dec 18 03:18:25 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 58D77C001B2 for ; Thu, 15 Dec 2022 00:14:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230003AbiLOAOv (ORCPT ); Wed, 14 Dec 2022 19:14:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229634AbiLOANq (ORCPT ); Wed, 14 Dec 2022 19:13:46 -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 64D99532FC for ; Wed, 14 Dec 2022 16:12:18 -0800 (PST) Received: by mail-pl1-x631.google.com with SMTP id s7so5138689plk.5 for ; Wed, 14 Dec 2022 16:12:18 -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=FZNFa0Som2cEXdyImA0PHzAPIxujgLNI2oeSKx5nHZI=; b=Mar/wnyOMbOk1+C6Q5uXoFrUdKfYUVRbk56ST4Cdpt8bBvB6kbwiHHlmlZHyoJqUXq 0bC2mxcb4Aba4AQ7l5WLkMe1+FiheB82JTvBZg70Btv3MIEnYkyusR0jImZrs5zZt2R4 WYPS2HBzWXj5LCp/LfNQb6K4VUdeyB2KhB+/8= 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=FZNFa0Som2cEXdyImA0PHzAPIxujgLNI2oeSKx5nHZI=; b=34Kf/Yom/wQz9fOXv5MGe6D1pBR9Wc/EKWScmVF0pZPw27T0kMVddjgzinrsUaZ24T ITh1KVi20IeRw9nkTNu9mUu2fVPRLAdtAU9ih/c4SORkIYRRb43b7s+/p2MQlILRUo3S T/c2jwHtuSncCHWG8u1SGtQSAGimyuGVoELD+I+VVagsL2PI+NoNDCL7S9dCfwZz908K Qg1vdljtetZ8TCtsheU27LoFOcN88Fga3+l6QO7FSdr+iUyKp2E/gvVF1lYKRE2sCgxH +kX1wGBLTQRuyU7qB7qrGqK3CFQeHw00+zLmqbunxj+vv/yOc0v1Ioyav9feIRZX950T C7yQ== X-Gm-Message-State: ANoB5pnCJ+lSgNNTzowvJ4e53mgv58XPRgLyJnf2m6Yi+HCQbKYB8xuL lgvKGS7cW1gk4M2dRP7QI5TKWw== X-Google-Smtp-Source: AA0mqf6GJzrv+PwU1r/NMlYDtOak9TKNkI9c0zXY6nAVkp4XlqigEungkSMJ1qEv73IT1BAvIE/pQw== X-Received: by 2002:a17:90a:7890:b0:221:4338:a6ae with SMTP id x16-20020a17090a789000b002214338a6aemr17461030pjk.33.1671063137955; Wed, 14 Dec 2022 16:12:17 -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 3-20020a17090a08c300b0021937b2118bsm1845738pjn.54.2022.12.14.16.12.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Dec 2022 16:12:17 -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, linux-security-module@vger.kernel.org Subject: [PATCH v8 4/5] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd Date: Thu, 15 Dec 2022 00:12:04 +0000 Message-Id: <20221215001205.51969-5-jeffxu@google.com> X-Mailer: git-send-email 2.39.0.rc1.256.g54fd8350bd-goog In-Reply-To: <20221215001205.51969-1-jeffxu@google.com> References: <20221215001205.51969-1-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.rc1.256.g54fd8350bd-goog