From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sat, 15 Jun 2019 08:57:31 -0400 From: "Theodore Ts'o" 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> 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 List-ID: 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