Message-ID: <YCXQGLUbE//ffIe7@google.com>
Date:   Fri, 12 Feb 2021 00:47:20 +0000
From:   Satya Tangirala <satyat@...gle.com>
To:     Mike Snitzer <snitzer@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com,
        Alasdair Kergon <agk@...hat.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH v4 0/5] add support for inline encryption to device mapper

On Thu, Feb 11, 2021 at 06:04:59PM -0500, Mike Snitzer wrote:
> On Thu, Feb 11 2021 at  6:01pm -0500,
> Satya Tangirala <satyat@...gle.com> wrote:
> 
> > On Wed, Feb 10, 2021 at 12:59:59PM -0700, Jens Axboe wrote:
> > > On 2/10/21 12:33 PM, Mike Snitzer wrote:
> > > > On Mon, Feb 01 2021 at 12:10am -0500,
> > > > Satya Tangirala <satyat@...gle.com> wrote:
> > > > 
> > > >> This patch series adds support for inline encryption to the device mapper.
> > > >>
> > > >> Patch 1 introduces the "passthrough" keyslot manager.
> > > >>
> > > >> The regular keyslot manager is designed for inline encryption hardware that
> > > >> have only a small fixed number of keyslots. A DM device itself does not
> > > >> actually have only a small fixed number of keyslots - it doesn't actually
> > > >> have any keyslots in the first place, and programming an encryption context
> > > >> into a DM device doesn't make much semantic sense. It is possible for a DM
> > > >> device to set up a keyslot manager with some "sufficiently large" number of
> > > >> keyslots in its request queue, so that upper layers can use the inline
> > > >> encryption capabilities of the DM device's underlying devices, but the
> > > >> memory being allocated for the DM device's keyslots is a waste since they
> > > >> won't actually be used by the DM device.
> > > >>
> > > >> The passthrough keyslot manager solves this issue - when the block layer
> > > >> sees that a request queue has a passthrough keyslot manager, it doesn't
> > > >> attempt to program any encryption context into the keyslot manager. The
> > > >> passthrough keyslot manager only allows the device to expose its inline
> > > >> encryption capabilities, and a way for upper layers to evict keys if
> > > >> necessary.
> > > >>
> > > >> There also exist inline encryption hardware that can handle encryption
> > > >> contexts directly, and allow users to pass them a data request along with
> > > >> the encryption context (as opposed to inline encryption hardware that
> > > >> require users to first program a keyslot with an encryption context, and
> > > >> then require the users to pass the keyslot index with the data request).
> > > >> Such devices can also make use of the passthrough keyslot manager.
> > > >>
> > > >> Patch 2 introduces some keyslot manager functions useful for the device
> > > >> mapper.
> > > >>
> > > >> Patch 3 introduces the changes for inline encryption support for the device
> > > >> mapper. A DM device only exposes the intersection of the crypto
> > > >> capabilities of its underlying devices. This is so that in case a bio with
> > > >> an encryption context is eventually mapped to an underlying device that
> > > >> doesn't support that encryption context, the blk-crypto-fallback's cipher
> > > >> tfms are allocated ahead of time by the call to blk_crypto_start_using_key.
> > > >>
> > > >> Each DM target can now also specify the "DM_TARGET_PASSES_CRYPTO" flag in
> > > >> the target type features to opt-in to supporting passing through the
> > > >> underlying inline encryption capabilities.  This flag is needed because it
> > > >> doesn't make much semantic sense for certain targets like dm-crypt to
> > > >> expose the underlying inline encryption capabilities to the upper layers.
> > > >> Again, the DM exposes inline encryption capabilities of the underlying
> > > >> devices only if all of them opt-in to passing through inline encryption
> > > >> support.
> > > >>
> > > >> A keyslot manager is created for a table when it is loaded. However, the
> > > >> mapped device's exposed capabilities *only* updated once the table is
> > > >> swapped in (until the new table is swapped in, the mapped device continues
> > > >> to expose the old table's crypto capabilities).
> > > >>
> > > >> This patch only allows the keyslot manager's capabilities to *expand*
> > > >> because of table changes. Any attempt to load a new table that doesn't
> > > >> support a crypto capability that the old table did is rejected.
> > > >>
> > > >> This patch also only exposes the intersection of the underlying device's
> > > >> capabilities, which has the effect of causing en/decryption of a bio to
> > > >> fall back to the kernel crypto API (if the fallback is enabled) whenever
> > > >> any of the underlying devices doesn't support the encryption context of the
> > > >> bio - it might be possible to make the bio only fall back to the kernel
> > > >> crypto API if the bio's target underlying device doesn't support the bio's
> > > >> encryption context, but the use case may be uncommon enough in the first
> > > >> place not to warrant worrying about it right now.
> > > >>
> > > >> Patch 4 makes DM evict a key from all its underlying devices when asked to
> > > >> evict a key.
> > > >>
> > > >> Patch 5 makes some DM targets opt-in to passing through inline encryption
> > > >> support. It does not (yet) try to enable this option with dm-raid, since
> > > >> users can "hot add" disks to a raid device, which makes this not completely
> > > >> straightforward (we'll need to ensure that any "hot added" disks must have
> > > >> a superset of the inline encryption capabilities of the rest of the disks
> > > >> in the raid device, due to the way Patch 2 of this series works).
> > > >>
> > > >> Changes v3 => v4:
> > > >>  - Allocate the memory for the ksm of the mapped device in
> > > >>    dm_table_complete(), and install the ksm in the md queue in __bind()
> > > >>    (as suggested by Mike). Also drop patch 5 from v3 since it's no longer
> > > >>    needed.
> > > >>  - Some cleanups
> > > >>
> > > >> Changes v2 => v3:
> > > >>  - Split up the main DM patch into 4 separate patches
> > > >>  - Removed the priv variable added to struct keyslot manager in v2
> > > >>  - Use a flag in target type features for opting-in to inline encryption
> > > >>    support, instead of using "may_passthrough_inline_crypto"
> > > >>  - cleanups, improve docs and restructure code
> > > >>
> > > >> Changes v1 => v2:
> > > >>  - Introduce private field to struct blk_keyslot_manager
> > > >>  - Allow the DM keyslot manager to expand its crypto capabilities if the
> > > >>    table is changed.
> > > >>  - Make DM reject table changes that would otherwise cause crypto
> > > >>    capabilities to be dropped.
> > > >>  - Allocate the DM device's keyslot manager only when at least one crypto
> > > >>    capability is supported (since a NULL value for q->ksm represents "no
> > > >>    crypto support" anyway).
> > > >>  - Remove the struct blk_keyslot_manager field from struct mapped_device.
> > > >>    This patch now relies on just directly setting up the keyslot manager in
> > > >>    the request queue, since each DM device is tied to only 1 queue.
> > > >>
> > > >> Satya Tangirala (5):
> > > >>   block: keyslot-manager: Introduce passthrough keyslot manager
> > > >>   block: keyslot-manager: Introduce functions for device mapper support
> > > >>   dm: add support for passing through inline crypto support
> > > >>   dm: support key eviction from keyslot managers of underlying devices
> > > >>   dm: set DM_TARGET_PASSES_CRYPTO feature for some targets
> > > >>
> > > >>  block/blk-crypto.c              |   1 +
> > > >>  block/keyslot-manager.c         | 146 ++++++++++++++++++++++
> > > >>  drivers/md/dm-core.h            |   5 +
> > > >>  drivers/md/dm-flakey.c          |   4 +-
> > > >>  drivers/md/dm-linear.c          |   5 +-
> > > >>  drivers/md/dm-table.c           | 210 ++++++++++++++++++++++++++++++++
> > > >>  drivers/md/dm.c                 |  18 ++-
> > > >>  include/linux/device-mapper.h   |  11 ++
> > > >>  include/linux/keyslot-manager.h |  11 ++
> > > >>  9 files changed, 407 insertions(+), 4 deletions(-)
> > > >>
> > > >> -- 
> > > >> 2.30.0.365.g02bc693789-goog
> > > >>
> > > > 
> > > > This set looks good to me now.
> > > > 
> > > > To avoid DM needing another rebase on block: Jens (and others), would
> > > > you like to review patches 1 and 2 (and reply with your Reviewed-by) so
> > > > I could pickup the DM required keyslot-manager changes along with
> > > > patches 3-5?
> > > 
> > > You can add my acked-by to 1+2 and queue it up.
> > > 
> > I resent the series (as v5) while addressing the comments Eric had on
> > Patch 3 (the changes were only to comments, so no functional
> > changes). I also added the acked/reviewed-bys.
> 
> I took care of Eric's comments.
> And I already staged these changes in linux-next for dm-5.12, see:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-5.12
> 
Ah, I didn't see that till a little while ago. Thanks!

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