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SubjectRe: [PATCH 2/3] dm: add support for passing through inline crypto support
On Wed, Sep 09 2020 at  7:44pm -0400,
Satya Tangirala <satyat@google.com> wrote:

> From: Eric Biggers <ebiggers@google.com>
>
> Update the device-mapper core to support exposing the inline crypto
> support of the underlying device(s) through the device-mapper device.
>
> This works by creating a "passthrough keyslot manager" for the dm
> device, which declares support for encryption settings which all
> underlying devices support. When a supported setting is used, the bio
> cloning code handles cloning the crypto context to the bios for all the
> underlying devices. When an unsupported setting is used, the blk-crypto
> fallback is used as usual.
>
> Crypto support on each underlying device is ignored unless the
> corresponding dm target opts into exposing it. This is needed because
> for inline crypto to semantically operate on the original bio, the data
> must not be transformed by the dm target. Thus, targets like dm-linear
> can expose crypto support of the underlying device, but targets like
> dm-crypt can't. (dm-crypt could use inline crypto itself, though.)
>
> When a key is evicted from the dm device, it is evicted from all
> underlying devices.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> Co-developed-by: Satya Tangirala <satyat@google.com>
> Signed-off-by: Satya Tangirala <satyat@google.com>
> ---
> block/blk-crypto.c | 1 +
> block/keyslot-manager.c | 34 ++++++++++++
> drivers/md/dm-core.h | 4 ++
> drivers/md/dm-table.c | 52 +++++++++++++++++++
> drivers/md/dm.c | 92 ++++++++++++++++++++++++++++++++-
> include/linux/device-mapper.h | 6 +++
> include/linux/keyslot-manager.h | 7 +++
> 7 files changed, 195 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-crypto.c b/block/blk-crypto.c
> index 2d5e60023b08..33555cf0e3e7 100644
> --- a/block/blk-crypto.c
> +++ b/block/blk-crypto.c
> @@ -402,3 +402,4 @@ int blk_crypto_evict_key(struct request_queue *q,
> */
> return blk_crypto_fallback_evict_key(key);
> }
> +EXPORT_SYMBOL_GPL(blk_crypto_evict_key);
> diff --git a/block/keyslot-manager.c b/block/keyslot-manager.c
> index 60ac406d54b9..e0f776c38d8a 100644
> --- a/block/keyslot-manager.c
> +++ b/block/keyslot-manager.c
> @@ -416,6 +416,40 @@ void blk_ksm_unregister(struct request_queue *q)
> {
> q->ksm = NULL;
> }
> +EXPORT_SYMBOL_GPL(blk_ksm_unregister);
> +
> +/**
> + * blk_ksm_intersect_modes() - restrict supported modes by child device
> + * @parent: The keyslot manager for parent device
> + * @child: The keyslot manager for child device, or NULL
> + *
> + * Clear any crypto mode support bits in @parent that aren't set in @child.
> + * If @child is NULL, then all parent bits are cleared.
> + *
> + * Only use this when setting up the keyslot manager for a layered device,
> + * before it's been exposed yet.
> + */
> +void blk_ksm_intersect_modes(struct blk_keyslot_manager *parent,
> + const struct blk_keyslot_manager *child)
> +{
> + if (child) {
> + unsigned int i;
> +
> + parent->max_dun_bytes_supported =
> + min(parent->max_dun_bytes_supported,
> + child->max_dun_bytes_supported);
> + for (i = 0; i < ARRAY_SIZE(child->crypto_modes_supported);
> + i++) {
> + parent->crypto_modes_supported[i] &=
> + child->crypto_modes_supported[i];
> + }
> + } else {
> + parent->max_dun_bytes_supported = 0;
> + memset(parent->crypto_modes_supported, 0,
> + sizeof(parent->crypto_modes_supported));
> + }
> +}
> +EXPORT_SYMBOL_GPL(blk_ksm_intersect_modes);
>
> /**
> * blk_ksm_init_passthrough() - Init a passthrough keyslot manager
> diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
> index c4ef1fceead6..4542050eebfc 100644
> --- a/drivers/md/dm-core.h
> +++ b/drivers/md/dm-core.h
> @@ -12,6 +12,7 @@
> #include <linux/kthread.h>
> #include <linux/ktime.h>
> #include <linux/blk-mq.h>
> +#include <linux/keyslot-manager.h>
>
> #include <trace/events/block.h>
>
> @@ -49,6 +50,9 @@ struct mapped_device {
>
> int numa_node_id;
> struct request_queue *queue;
> +#ifdef CONFIG_BLK_INLINE_ENCRYPTION
> + struct blk_keyslot_manager ksm;
> +#endif
>
> atomic_t holders;
> atomic_t open_count;

Any reason you placed the ksm member where you did?

Looking at 'struct blk_keyslot_manager' I'm really hating adding that
bloat to every DM device for a feature that really won't see much broad
use (AFAIK).

Any chance you could allocate 'struct blk_keyslot_manager' as needed so
that most users of DM would only be carrying 1 extra pointer (set to
NULL)?

Thanks,
Mike

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