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Date:   Thu, 11 Feb 2021 23:01:30 +0000
From:   Satya Tangirala <satyat@google.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Mike Snitzer <snitzer@redhat.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, dm-devel@redhat.com,
        Alasdair Kergon <agk@redhat.com>,
        Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH v4 0/5] add support for inline encryption to device mapper
Message-ID: <YCW3SlbDFNn+Xyac@google.com>
References: <20210201051019.1174983-1-satyat@google.com>
 <20210210193327.GA8226@redhat.com>
 <c681d976-f1bd-482c-8ead-b099986b70e5@kernel.dk>
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In-Reply-To: <c681d976-f1bd-482c-8ead-b099986b70e5@kernel.dk>
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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@google.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.
> -- 
> Jens Axboe
>