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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT 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 1E6DBC31E52 for ; Sat, 15 Jun 2019 12:57:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E985821773 for ; Sat, 15 Jun 2019 12:57:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726511AbfFOM55 (ORCPT ); Sat, 15 Jun 2019 08:57:57 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:37891 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725999AbfFOM55 (ORCPT ); Sat, 15 Jun 2019 08:57:57 -0400 Received: from callcc.thunk.org (rrcs-74-87-88-165.west.biz.rr.com [74.87.88.165]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id x5FCvWOZ003473 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sat, 15 Jun 2019 08:57:33 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id 0D4F8420484; Sat, 15 Jun 2019 08:57:32 -0400 (EDT) Date: Sat, 15 Jun 2019 08:57:31 -0400 From: "Theodore Ts'o" To: Eric Biggers Cc: linux-fscrypt@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, Jaegeuk Kim , Victor Hsieh , Dave Chinner , Christoph Hellwig , "Darrick J . Wong" , Linus Torvalds Subject: Re: [PATCH v4 05/16] fs-verity: add Kconfig and the helper functions for hashing Message-ID: <20190615125731.GF6142@mit.edu> References: <20190606155205.2872-1-ebiggers@kernel.org> <20190606155205.2872-6-ebiggers@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190606155205.2872-6-ebiggers@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Thu, Jun 06, 2019 at 08:51:54AM -0700, Eric Biggers wrote: > From: Eric Biggers > > Add the beginnings of the fs/verity/ support layer, including the > Kconfig option and various helper functions for hashing. To start, only > SHA-256 is supported, but other hash algorithms can easily be added. > > Signed-off-by: Eric Biggers Looks good; you can add: Reviewed-off-by: Theodore Ts'o One thought for consideration below... > + > +/* > + * Maximum depth of the Merkle tree. Up to 64 levels are theoretically possible > + * with a very small block size, but we'd like to limit stack usage during > + * verification, and in practice this is plenty. E.g., with SHA-256 and 4K > + * blocks, a file with size UINT64_MAX bytes needs just 8 levels. > + */ > +#define FS_VERITY_MAX_LEVELS 16 Maybe we should make FS_VERITY_MAX_LEVELS 8 for now? This is an implementation-level restriction, and currently we don't support any architectures that have a page size < 4k. We can always bump this number up in the future if it ever becomes necessary, and limiting max levels to 8 saves almost 100 bytes of stack space in verify_page(). - Ted