From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: Re: [PATCH] Add an option to dm-verity to validate hashes at most once Date: Wed, 14 Mar 2018 12:09:57 -0700 Message-ID: <20180314190957.GB183724@google.com> References: <20180306231456.210504-1-totte@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180306231456.210504-1-totte@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Patrik Torstensson Cc: Alasdair Kergon , Mike Snitzer , dm-devel@redhat.com, linux-kernel@vger.kernel.org, samitolvanen@google.com, gkaiser@google.com, paulcrowley@google.com List-Id: dm-devel.ids Hi Patrik, On Tue, Mar 06, 2018 at 03:14:56PM -0800, Patrik Torstensson wrote: > Add an option to dm-verity to validate hashes at most once > to allow platforms that is CPU/memory contraint to be > protected by dm-verity against offline attacks. > > The option introduces a bitset that is used to check if > a block has been validated before or not. A block can > be validated more than once as there is no thread protection > for the bitset. > > This patch has been developed and tested on entry-level > Android Go devices. > > Signed-off-by: Patrik Torstensson > --- > drivers/md/dm-verity-target.c | 58 +++++++++++++++++++++++++++++++++-- > drivers/md/dm-verity.h | 1 + > 2 files changed, 56 insertions(+), 3 deletions(-) The new option needs to be documented in Documentation/device-mapper/verity.txt, including a description of what the option does as well as how it affects the security properties of dm-verity. There should also be a mention of why the option applies to data blocks but not hash blocks, assuming that's intentional. verity_status() also needs to be updated to show the new option, otherwise it will not be visible via the DM_TABLE_STATUS ioctl ('dmsetup table' on the command line). Also the minor version number in the struct target_type needs to be incremented, so that userspace can determine whether the option is supported. > > for (b = 0; b < io->n_blocks; b++) { > int r; > + sector_t cur_block = io->block + b; > struct ahash_request *req = verity_io_hash_req(v, io); > > + if (v->validated_blocks && > + likely(test_bit(cur_block, v->validated_blocks))) { > + verity_bv_skip_block(v, io, &io->iter); > + continue; > + } > + > r = verity_hash_for_block(v, io, io->block + b, Can you replace 'io->block + b' with 'cur_block' here as well? Thanks, - Eric