From patchwork Thu Jun 29 00:29:42 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sweet Tea Dorminy X-Patchwork-Id: 13296481 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 05742EB64DD for ; Thu, 29 Jun 2023 00:34:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230526AbjF2Ae4 (ORCPT ); Wed, 28 Jun 2023 20:34:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58414 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231169AbjF2Aey (ORCPT ); Wed, 28 Jun 2023 20:34:54 -0400 Received: from box.fidei.email (box.fidei.email [IPv6:2605:2700:0:2:a800:ff:feba:dc44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 918681FC2; Wed, 28 Jun 2023 17:34:53 -0700 (PDT) Received: from authenticated-user (box.fidei.email [71.19.144.250]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (No client certificate requested) by box.fidei.email (Postfix) with ESMTPSA id 9927680727; Wed, 28 Jun 2023 20:34:52 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=dorminy.me; s=mail; t=1687998893; bh=OU3phguMvW6dB4K+YYW4zI9XIY0ZO0OgTtdZGLxn5UQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wi8h+uGAIz/FpxQu/0pNrDjn1DWsZPLLMzZh0kkftOfnJqbbEhR8TZreMaxjqk1wq CS1M3LmqKIKwdZy8FgZmsEi1ys5eaSmYaWGdAhq+h41X+zGDfrg2M8py/sS/JICzBW omL+N7XwTTs5ePXlW+4jcyTdr2+QpVRIagnAhjdrE2Qc0v+mVxX7W41ncKs6XmZeaL drvSDATB4/7UGbMc7ygfDzniu26pD6RRS+S9WPBAOQSgrADtFoJqmDQn6mA9D9ndrC BBbGod9ruSNpKkGfPjmGMMAEsvb4oVQClhOxvfbh1Fh9qR+ym4hHWxnFkj+W8unzCN qS7uz5MYDNshg== From: Sweet Tea Dorminy To: Chris Mason , Josef Bacik , David Sterba , Eric Biggers , "Theodore Y. Ts'o" , Jaegeuk Kim , kernel-team@meta.com, linux-btrfs@vger.kernel.org, linux-fscrypt@vger.kernel.org Cc: Sweet Tea Dorminy Subject: [PATCH v1 12/12] fscrypt: update documentation for per-extent keys Date: Wed, 28 Jun 2023 20:29:42 -0400 Message-Id: <212cb3d0b8f4abf657671f05dbe0b3d9d858211d.1687988246.git.sweettea-kernel@dorminy.me> In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Add some documentation of how extent-based encryption works, hopefully enough for future filesystem users. Signed-off-by: Sweet Tea Dorminy --- Documentation/filesystems/fscrypt.rst | 38 ++++++++++++++++++++++----- 1 file changed, 32 insertions(+), 6 deletions(-) diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index eccd327e6df5..9bbfcd84a29f 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -31,7 +31,7 @@ However, except for filenames, fscrypt does not encrypt filesystem metadata. Unlike eCryptfs, which is a stacked filesystem, fscrypt is integrated -directly into supported filesystems --- currently ext4, F2FS, and +directly into supported filesystems --- currently btrfs, ext4, F2FS, and UBIFS. This allows encrypted files to be read and written without caching both the decrypted and encrypted pages in the pagecache, thereby nearly halving the memory used and bringing it in line with @@ -280,6 +280,11 @@ included in the IV. Moreover: key derived using the KDF. Users may use the same master key for other v2 encryption policies. +For filesystems with extent-based content encryption (e.g. btrfs), +this is the only choice. Data shared among multiple inodes must share +the exact same key, therefore necessitating inodes using the same key +for contents encryption. + IV_INO_LBLK_64 policies ----------------------- @@ -381,12 +386,13 @@ to individual filesystems. However, authenticated encryption (AE) modes are not currently supported because of the difficulty of dealing with ciphertext expansion. -Contents encryption -------------------- +Inode-based contents encryption +------------------------------- -For file contents, each filesystem block is encrypted independently. -Starting from Linux kernel 5.5, encryption of filesystems with block -size less than system's page size is supported. +Most filesystems use the previously discussed per-file keys. For these +filesystems, for file contents, each filesystem block is encrypted +independently. Starting from Linux kernel 5.5, encryption of filesystems +with block size less than system's page size is supported. Each block's IV is set to the logical block number within the file as a little endian number, except that: @@ -410,6 +416,26 @@ Note that because file logical block numbers are included in the IVs, filesystems must enforce that blocks are never shifted around within encrypted files, e.g. via "collapse range" or "insert range". +Extent-based contents encryption +-------------------------------- + +For certain filesystems (currently only btrfs), data is encrypted on a +per-extent basis, for whatever the filesystem's notion of an extent is. The +scheme is exactly as with inode-based contents encryption, except that the +'inode number' for an extent is requested from the filesystem instead of from +the file's inode, and the 'logical block number' refers to an offset within the +extent. + +Because the encryption material is per-extent instead of per-inode, as long +as the extent's encryption context does not change, the filesystem may shift +around the position of the extent, and may have multiple files referring to +the same encrypted extent. + +Not all extents within a file are decrypted simultaneously, so it is possible +for a file read to fail partway through the file if it crosses into an extent +whose key is unavailable. However, all writes will succeed, unless the key is +removed mid-write. + Filenames encryption --------------------