From patchwork Fri Aug 5 22:21:23 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Xu X-Patchwork-Id: 12937860 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 EC8EDC25B08 for ; Fri, 5 Aug 2022 22:21:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241755AbiHEWV6 (ORCPT ); Fri, 5 Aug 2022 18:21:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36346 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241845AbiHEWVv (ORCPT ); Fri, 5 Aug 2022 18:21:51 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EF1331C920 for ; Fri, 5 Aug 2022 15:21:50 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-31f4e870a17so31513517b3.9 for ; Fri, 05 Aug 2022 15:21:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=5E4PGAWMReAFHkj0eA7xzWpJk8N5M4FgV4LT8CvMVPA=; b=TDuzZmP48qciezv1MXsf3LVuEa0sxCTwiXmz3GaFb6bY9Qtk1DrEr4hk/hgSUCSU9D AfNdO6ggJ2vgmMWeMOlX/leMgSXGcQVjNK0zYR0phfm+32xYcPAHGvQSYoqPiNbxudnk HvE2bkCtTLZ4+b3Ay+j53c5ejYOvr0jzKdc8h62ng9xyA/YGHmq7HQjrLzA1ZaYH+BV9 0FZ6JoFGedju30kgJTOIXqXWVdCHFjQ55uchR5QBZO9lhMl46oSxaKE6Z0a+P78bLdDl tNj+/17Hexg7tUbRBM+OCbb+sqB6gZJt9lxBqysd3REOSfOgCXMUXOEiZd1Awo0K8DSt 9wmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=5E4PGAWMReAFHkj0eA7xzWpJk8N5M4FgV4LT8CvMVPA=; b=rOW/jHzWE8qvBu3UFLpsDYdnBr3APbHLW/uC3BbyziUxLzp3JIfHYNKW5GWxj3T/cu qRUiUYF/SyWNvKM4YbP7+2PIEQ448giht6SdXxMc8foZU4cZV8H4zgqvryNvyq3hryFD PNTUYbaAxy9+1qE1UIpPfilMvJYY8kDghLDqNAAiPk1tC47DXBLMvz5gnCVWLBmLnUXR ga8d9uMw1l3D46TOUMvzlZBii2zahrjnxyy7GSY1tMHmUMhDgcN+7eKvBXb7cVXSSXVj G690AmppyoHG9XkRxGfOOfxYEMTLAd/wjhjDcwwH+6Y/d/S6nTdglPG9msQpZYUZiz7H ip/w== X-Gm-Message-State: ACgBeo0toGgEVHGOsHkSYT6AQYu9pH/P9cYZnEVwkbicZSfKz0EsnNHz BqaVx/SyGmZ9PcRn4YT5KVu33x56DZE= X-Google-Smtp-Source: AA6agR55Nd+GF+Zicb9UzLXVsBAJG/nkDrQRMgHX77YRUR2vsXmmAEpB7Hc955x1MuY3F3Ah7dc0fEbCssM= X-Received: from jeffxud.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:e37]) (user=jeffxu job=sendgmr) by 2002:a25:9c87:0:b0:671:82fd:9106 with SMTP id y7-20020a259c87000000b0067182fd9106mr7167620ybo.546.1659738110679; Fri, 05 Aug 2022 15:21:50 -0700 (PDT) Date: Fri, 5 Aug 2022 22:21:23 +0000 In-Reply-To: <20220805222126.142525-1-jeffxu@google.com> Message-Id: <20220805222126.142525-3-jeffxu@google.com> Mime-Version: 1.0 References: <20220805222126.142525-1-jeffxu@google.com> X-Mailer: git-send-email 2.37.1.559.g78731f0fdb-goog Subject: [PATCH v2 2/5] mm/memfd: add MFD_NOEXEC flag to memfd_create From: To: skhan@linuxfoundation.org Cc: akpm@linux-foundation.org, dmitry.torokhov@gmail.com, dverkamp@chromium.org, hughd@google.com, jeffxu@google.com, jorgelo@chromium.org, keescook@chromium.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, mnissler@chromium.org, jannh@google.com, Jeff Xu Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org From: Daniel Verkamp The new MFD_NOEXEC flag allows the creation of a permanently non-executable memfd. This is accomplished by creating it with a different set of file mode bits (0666) than the default (0777) and applying the F_SEAL_EXEC seal at creation time, so there is no window between memfd creation and seal application. Unfortunately, the default for memfd must remain executable, since changing this would be an API break, and some programs depend on being able to exec code from a memfd directly. However, this new flag will allow programs to create non-executable memfds, and a distribution may choose to enforce use of this flag in memfd_create calls via other security mechanisms. Co-developed-by: Jeff Xu Signed-off-by: Jeff Xu Signed-off-by: Daniel Verkamp --- include/uapi/linux/memfd.h | 1 + mm/memfd.c | 10 +++++++++- 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h index 7a8a26751c23..140e125c9f65 100644 --- a/include/uapi/linux/memfd.h +++ b/include/uapi/linux/memfd.h @@ -8,6 +8,7 @@ #define MFD_CLOEXEC 0x0001U #define MFD_ALLOW_SEALING 0x0002U #define MFD_HUGETLB 0x0004U +#define MFD_NOEXEC 0x0008U /* * Huge page size encoding when MFD_HUGETLB is specified, and a huge page diff --git a/mm/memfd.c b/mm/memfd.c index 4ebeab94aa74..b841514eb0fd 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -263,7 +263,7 @@ long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg) #define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1) #define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN) -#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB) +#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | MFD_NOEXEC) SYSCALL_DEFINE2(memfd_create, const char __user *, uname, @@ -333,6 +333,14 @@ SYSCALL_DEFINE2(memfd_create, *file_seals &= ~F_SEAL_SEAL; } + if (flags & MFD_NOEXEC) { + struct inode *inode = file_inode(file); + + inode->i_mode &= ~0111; + file_seals = memfd_file_seals_ptr(file); + *file_seals |= F_SEAL_EXEC; + } + fd_install(fd, file); kfree(name); return fd;