From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B2867C433E1 for ; Tue, 19 May 2020 14:45:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92408207FB for ; Tue, 19 May 2020 14:45:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589899504; bh=IaVjtUjZRfD5n9+imvde6GZIZTX/UXJ/zi0G9EtqwY8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=2bpSSGPiuShcX8+nwnmzhVZM5EU1AE94z9YwGNRtb5XMelu1Q4CvWPqxBy2XcciPO SO0jt0/AuWaMLzRSard16q6PQFjJUPzw/HWJkc0SUQRqXurb7AJx0eplKZ1TtgHhYK ll6gliu/YhAGoSKQa+CrZJjqNW7nExh86dyYF9RY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729133AbgESOpE (ORCPT ); Tue, 19 May 2020 10:45:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:44100 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728647AbgESOpE (ORCPT ); Tue, 19 May 2020 10:45:04 -0400 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BB3C920825; Tue, 19 May 2020 14:45:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589899503; bh=IaVjtUjZRfD5n9+imvde6GZIZTX/UXJ/zi0G9EtqwY8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mJzQ71AZohKqnmu/hIb1vJojWlq7pnCYd6ePvm+HoHwhRH6gnFUNWLJbDW6vXlxy+ Sjjoqco6E4dO0ac3gZYa7/CYDGb5rG1spEg7Ug7kjnlZETQtiS4HugobFC8VDghAls srvR1sb43gH1vlDywH6XqoHrdvbMx4qhRYGcQXCE= Date: Tue, 19 May 2020 07:45:01 -0700 From: Eric Biggers To: "Theodore Y. Ts'o" Cc: linux-fscrypt@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-crypto@vger.kernel.org, linux-mmc@vger.kernel.org, Satya Tangirala , Jaegeuk Kim , Paul Crowley Subject: Re: [PATCH] fscrypt: add support for IV_INO_LBLK_32 policies Message-ID: <20200519144501.GA857@sol.localdomain> References: <20200515204141.251098-1-ebiggers@kernel.org> <20200519111321.GE2396055@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200519111321.GE2396055@mit.edu> Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Tue, May 19, 2020 at 07:13:21AM -0400, Theodore Y. Ts'o wrote: > On Fri, May 15, 2020 at 01:41:41PM -0700, Eric Biggers wrote: > > From: Eric Biggers > > > > The eMMC inline crypto standard will only specify 32 DUN bits (a.k.a. IV > > bits), unlike UFS's 64. IV_INO_LBLK_64 is therefore not applicable, but > > an encryption format which uses one key per policy and permits the > > moving of encrypted file contents (as f2fs's garbage collector requires) > > is still desirable. > > > > To support such hardware, add a new encryption format IV_INO_LBLK_32 > > that makes the best use of the 32 bits: the IV is set to > > 'SipHash-2-4(inode_number) + file_logical_block_number mod 2^32', where > > the SipHash key is derived from the fscrypt master key. We hash only > > the inode number and not also the block number, because we need to > > maintain contiguity of DUNs to merge bios. > > > > Unlike with IV_INO_LBLK_64, with this format IV reuse is possible; this > > is unavoidable given the size of the DUN. This means this format should > > only be used where the requirements of the first paragraph apply. > > However, the hash spreads out the IVs in the whole usable range, and the > > use of a keyed hash makes it difficult for an attacker to determine > > which files use which IVs. > > > > Besides the above differences, this flag works like IV_INO_LBLK_64 in > > that on ext4 it is only allowed if the stable_inodes feature has been > > enabled to prevent inode numbers and the filesystem UUID from changing. > > > > Signed-off-by: Eric Biggers > > Reviewed-by: Theodore Ts'o > > I kind of wish we had Kunit tests with test vectors, but that's for > another commit I think. > We do have ciphertext verification tests in xfstests for all the existing fscrypt options. Actually, I had hacked one together for IV_INO_LBLK_32 before sending this patch (https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/xfstests-dev.git/commit/?id=55153ceee2948269c0359bd97fc0d58a26139c87). I'll be sending it for review after I've looked over it again. Similarly, since earlier this year, we now also have ciphertext verification tests in Android's VTS (Vendor Test Suite) (https://android.googlesource.com/platform/test/vts-testcase/kernel/+/refs/heads/master/encryption/). I'll be adding one for this new flag. These ciphertext verification tests test the round-trip from the key added by userspace to the data on-disk -- even if the data is encrypted by inline crypto hardware rather than the kernel itself. So they're better than Kunit tests. The thing I'm struggling with a bit is actually that when inline crypto is used, IV_INO_LBLK_32 introduces a case where the DUN can wrap from 0xffffffff to 0, and that case is new/special in that blocks can't be merged over that boundary even if they are both logically and physically contiguous. So, we could also use a test that tests doing I/O around this boundary where the DUN wraps around. - Eric