From patchwork Fri Jun 10 00:06:16 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 12876225 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 CF9ECC433EF for ; Fri, 10 Jun 2022 00:07:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234350AbiFJAHO (ORCPT ); Thu, 9 Jun 2022 20:07:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56420 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232136AbiFJAHN (ORCPT ); Thu, 9 Jun 2022 20:07:13 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DDE131E4B55; Thu, 9 Jun 2022 17:07:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7D1A460B43; Fri, 10 Jun 2022 00:07:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CFAE2C34115; Fri, 10 Jun 2022 00:07:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1654819631; bh=jIjBc8E9Fs1woT9Va1+rxlmfiKvnSnF0c/ckjor99Ig=; h=From:To:Cc:Subject:Date:From; b=WABC9AeeF2HCEspdURfAgc9vU5VbmERg0juPQn34+rtbWg1JQiMuLYws2X1/YyChx FK2UpxjessiGMvhZNNTZqexUcKGc7MsZKLEYxAVirH6VQIphlqPR7zAA9QSJW67nmB qeXzEMpcsDMNRL3kDOTm1ms6Q1W4WFvcEpAdv7hKtPYgLpTsJMA1cxpZxNaGKDSyv0 6rM/yFe8b3miiZkvhNKd2piyqzwu5egcsElaPMyMe0AH3enNgMnoqsAte2uFCIIKZP HO8sisnXk4vudxiXa4P4QdEi7rm6MJ+t8F8Xs5oY2gzb435bqMAMrHNs68WN6pbIa0 GrQ92zlN2RXrA== From: Eric Biggers To: linux-fscrypt@vger.kernel.org Cc: linux-btrfs@vger.kernel.org Subject: [PATCH] fs-verity: mention btrfs support Date: Thu, 9 Jun 2022 17:06:16 -0700 Message-Id: <20220610000616.18225-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.36.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fscrypt@vger.kernel.org From: Eric Biggers btrfs supports fs-verity since Linux v5.15. Document this. Signed-off-by: Eric Biggers Acked-by: David Sterba --- Documentation/filesystems/fsverity.rst | 53 +++++++++++++++----------- fs/verity/Kconfig | 10 ++--- 2 files changed, 35 insertions(+), 28 deletions(-) diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst index 756f2c215ba13..cb8e7573882a1 100644 --- a/Documentation/filesystems/fsverity.rst +++ b/Documentation/filesystems/fsverity.rst @@ -11,9 +11,9 @@ Introduction fs-verity (``fs/verity/``) is a support layer that filesystems can hook into to support transparent integrity and authenticity protection -of read-only files. Currently, it is supported by the ext4 and f2fs -filesystems. Like fscrypt, not too much filesystem-specific code is -needed to support fs-verity. +of read-only files. Currently, it is supported by the ext4, f2fs, and +btrfs filesystems. Like fscrypt, not too much filesystem-specific +code is needed to support fs-verity. fs-verity is similar to `dm-verity `_ @@ -473,9 +473,9 @@ files being swapped around. Filesystem support ================== -fs-verity is currently supported by the ext4 and f2fs filesystems. -The CONFIG_FS_VERITY kconfig option must be enabled to use fs-verity -on either filesystem. +fs-verity is supported by several filesystems, described below. The +CONFIG_FS_VERITY kconfig option must be enabled to use fs-verity on +any of these filesystems. ``include/linux/fsverity.h`` declares the interface between the ``fs/verity/`` support layer and filesystems. Briefly, filesystems @@ -544,6 +544,13 @@ Currently, f2fs verity only supports a Merkle tree block size of 4096. Also, f2fs doesn't support enabling verity on files that currently have atomic or volatile writes pending. +btrfs +----- + +btrfs supports fs-verity since Linux v5.15. Verity-enabled inodes are +marked with a RO_COMPAT inode flag, and the verity metadata is stored +in separate btree items. + Implementation details ====================== @@ -622,14 +629,14 @@ workqueue, and then the workqueue work does the decryption or verification. Finally, pages where no decryption or verity error occurred are marked Uptodate, and the pages are unlocked. -Files on ext4 and f2fs may contain holes. Normally, ``->readahead()`` -simply zeroes holes and sets the corresponding pages Uptodate; no bios -are issued. To prevent this case from bypassing fs-verity, these -filesystems use fsverity_verify_page() to verify hole pages. +On many filesystems, files can contain holes. Normally, +``->readahead()`` simply zeroes holes and sets the corresponding pages +Uptodate; no bios are issued. To prevent this case from bypassing +fs-verity, these filesystems use fsverity_verify_page() to verify hole +pages. -ext4 and f2fs disable direct I/O on verity files, since otherwise -direct I/O would bypass fs-verity. (They also do the same for -encrypted files.) +Filesystems also disable direct I/O on verity files, since otherwise +direct I/O would bypass fs-verity. Userspace utility ================= @@ -648,7 +655,7 @@ Tests To test fs-verity, use xfstests. For example, using `kvm-xfstests `_:: - kvm-xfstests -c ext4,f2fs -g verity + kvm-xfstests -c ext4,f2fs,btrfs -g verity FAQ === @@ -771,15 +778,15 @@ weren't already directly answered in other parts of this document. e.g. magically trigger construction of a Merkle tree. :Q: Does fs-verity support remote filesystems? -:A: Only ext4 and f2fs support is implemented currently, but in - principle any filesystem that can store per-file verity metadata - can support fs-verity, regardless of whether it's local or remote. - Some filesystems may have fewer options of where to store the - verity metadata; one possibility is to store it past the end of - the file and "hide" it from userspace by manipulating i_size. The - data verification functions provided by ``fs/verity/`` also assume - that the filesystem uses the Linux pagecache, but both local and - remote filesystems normally do so. +:A: So far all filesystems that have implemented fs-verity support are + local filesystems, but in principle any filesystem that can store + per-file verity metadata can support fs-verity, regardless of + whether it's local or remote. Some filesystems may have fewer + options of where to store the verity metadata; one possibility is + to store it past the end of the file and "hide" it from userspace + by manipulating i_size. The data verification functions provided + by ``fs/verity/`` also assume that the filesystem uses the Linux + pagecache, but both local and remote filesystems normally do so. :Q: Why is anything filesystem-specific at all? Shouldn't fs-verity be implemented entirely at the VFS level? diff --git a/fs/verity/Kconfig b/fs/verity/Kconfig index 54598cd801457..aad1f1d998b9d 100644 --- a/fs/verity/Kconfig +++ b/fs/verity/Kconfig @@ -14,11 +14,11 @@ config FS_VERITY help This option enables fs-verity. fs-verity is the dm-verity mechanism implemented at the file level. On supported - filesystems (currently EXT4 and F2FS), userspace can use an - ioctl to enable verity for a file, which causes the filesystem - to build a Merkle tree for the file. The filesystem will then - transparently verify any data read from the file against the - Merkle tree. The file is also made read-only. + filesystems (currently ext4, f2fs, and btrfs), userspace can + use an ioctl to enable verity for a file, which causes the + filesystem to build a Merkle tree for the file. The filesystem + will then transparently verify any data read from the file + against the Merkle tree. The file is also made read-only. This serves as an integrity check, but the availability of the Merkle tree root hash also allows efficiently supporting