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=1.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, FSL_HELO_FAKE,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=no 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 D9D1AC31E5B for ; Tue, 18 Jun 2019 17:51:30 +0000 (UTC) Received: from lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B2873205F4; Tue, 18 Jun 2019 17:51:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sourceforge.net header.i=@sourceforge.net header.b="BEt+1I2H"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sf.net header.i=@sf.net header.b="eHwpKUHS"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="jN+UHuS7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2873205F4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-f2fs-devel-bounces@lists.sourceforge.net Received: from [127.0.0.1] (helo=sfs-ml-1.v29.lw.sourceforge.com) by sfs-ml-1.v29.lw.sourceforge.com with esmtp (Exim 4.90_1) (envelope-from ) id 1hdIGZ-0002yi-3s; Tue, 18 Jun 2019 17:51:31 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-1.v29.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1hdIGY-0002yV-9r for linux-f2fs-devel@lists.sourceforge.net; Tue, 18 Jun 2019 17:51:30 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=In-Reply-To:Content-Type:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=dkzOcDvDPbAqqbSn4IkzRsM/a1UOBs/mqOL3uFyjONY=; b=BEt+1I2HZHk9s+yvtRc3BDfY63 7HYhGE1tcTI+/BYLpoGsvRCyf0laty7wtdTeNmRKT37eCbaTa7FJwKXCoo4Un3fHbexoL8SnJPUhk jXVGE2IqyrF/S2JBI/HUw8snv48MASjECsXb6fb9oEqKnYNcZPvtT7M/KmEOdDXYwbpI=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To :From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=dkzOcDvDPbAqqbSn4IkzRsM/a1UOBs/mqOL3uFyjONY=; b=eHwpKUHSMBStzJP3X1zAviZ7Qm YEc8k+IuENAf1FD1dzsrk5meK27ZyAC2m23iHtw+Ly4Nzl7/dip+2XW2Rw7kDUnx5Uehc4anpdPmW CyEQR9o/qB4A5cwtWUcxD5FzB1P3+SSQu7fLjRbFI4lQ5RYE86FLeV1EqIufv6Wv+OXk=; Received: from mail.kernel.org ([198.145.29.99]) by sfi-mx-1.v28.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) id 1hdIGU-00FrEA-N9 for linux-f2fs-devel@lists.sourceforge.net; Tue, 18 Jun 2019 17:51:29 +0000 Received: from gmail.com (unknown [104.132.1.77]) (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 E84DC205F4; Tue, 18 Jun 2019 17:51:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560880280; bh=+JwMW+EfA+1KPkG7+F9JNJm/PdgIsMm+vsIk5VyMsXU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jN+UHuS7ftaLSzRz/uIHx1sk5q1R1x1AoYmkjyFeRGM23VC4+ycH6vhtDO6U3CLbJ QF9MEni6U1cDt7guNvx25VfpXPIjhqjCq5psE955shlVQKm+NnVxKNBEUDRsVxFZbD NijVFVXBjZzTi6Rjldw9aQ2M2ZOZ8+cRambf8Z+A= Date: Tue, 18 Jun 2019 10:51:18 -0700 From: Eric Biggers To: Theodore Ts'o Message-ID: <20190618175117.GF184520@gmail.com> References: <20190606155205.2872-1-ebiggers@kernel.org> <20190606155205.2872-15-ebiggers@kernel.org> <20190615153112.GO6142@mit.edu> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190615153112.GO6142@mit.edu> User-Agent: Mutt/1.10.1 (2018-07-13) X-Headers-End: 1hdIGU-00FrEA-N9 Subject: Re: [f2fs-dev] [PATCH v4 14/16] ext4: add basic fs-verity support X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Darrick J . Wong" , linux-api@vger.kernel.org, Dave Chinner , linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jaegeuk Kim , linux-integrity@vger.kernel.org, linux-ext4@vger.kernel.org, Linus Torvalds , Christoph Hellwig , Victor Hsieh Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Sat, Jun 15, 2019 at 11:31:12AM -0400, Theodore Ts'o wrote: > On Thu, Jun 06, 2019 at 08:52:03AM -0700, Eric Biggers wrote: > > +/* > > + * Format of ext4 verity xattr. This points to the location of the verity > > + * descriptor within the file data rather than containing it directly because > > + * the verity descriptor *must* be encrypted when ext4 encryption is used. But, > > + * ext4 encryption does not encrypt xattrs. > > + */ > > +struct fsverity_descriptor_location { > > + __le32 version; > > + __le32 size; > > + __le64 pos; > > +}; > > What's the benefit of storing the location in an xattr as opposed to > just keying it off the end of i_size, rounded up to next page size (or > 64k) as I had suggested earlier? > > Using an xattr burns xattr space, which is a limited resource, and it > adds some additional code complexity. Does the benefits outweigh the > added complexity? > > - Ted It means that only the fs/verity/ support layer has to be aware of the format of the fsverity_descriptor, and the filesystem can just treat it an as opaque blob. Otherwise the filesystem would need to read the first 'sizeof(struct fsverity_descriptor)' bytes and use those to calculate the size as 'sizeof(struct fsverity_descriptor) + le32_to_cpu(desc.sig_size)', then read the rest. Is this what you have in mind? Alternatively the filesystem could prepend the fsverity_descriptor with its size, similar to how in the v1 and v2 patchsets there was an fsverity_footer appended to the fsverity_descriptor. But an xattr seems a cleaner approach to store a few bytes that don't need to be encrypted. Putting the verity descriptor before the Merkle tree also means that we'd have to pass the desc_size to ->begin_enable_verity(), ->read_merkle_tree_page(), and ->write_merkle_tree_block(), versus just passing the merkle_tree_size to ->end_enable_verity(). This would be easy, but it would still add a bit of complexity in the fsverity_operations rather than reduce it. It's also somewhat nice to have the version number in the xattr, in case we ever introduce a new fs-verity format for ext4 or f2fs. So to me, it doesn't seem like the other possible solutions are better. - Eric _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel