Message-ID: <c681d976-f1bd-482c-8ead-b099986b70e5@kernel.dk>
Date:   Wed, 10 Feb 2021 12:59:59 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Mike Snitzer <snitzer@...hat.com>,
        Satya Tangirala <satyat@...gle.com>
Cc:     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 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.

-- 
Jens Axboe

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