dm: add support for passing through inline crypto support

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.)

A DM device's table can only be changed if the "new" inline encryption
capabilities are a (*not* necessarily strict) superset of the "old" inline
encryption capabilities.  Attempts to make changes to the table that result
in some inline encryption capability becoming no longer supported will be
rejected.

For the sake of clarity, key eviction from underlying devices will be
handled in a future patch.

Co-developed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 61a66fb8ebb3..47588130ef5e 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -257,6 +257,12 @@ struct target_type {
 #define DM_TARGET_NOWAIT		0x00000080
 #define dm_target_supports_nowait(type) ((type)->features & DM_TARGET_NOWAIT)
 
+/*
+ * A target supports passing through inline crypto support.
+ */
+#define DM_TARGET_PASSES_CRYPTO		0x00000100
+#define dm_target_passes_crypto(type) ((type)->features & DM_TARGET_PASSES_CRYPTO)
+
 struct dm_target {
 	struct dm_table *table;
 	struct target_type *type;
@@ -534,6 +540,11 @@ struct dm_table *dm_swap_table(struct mapped_device *md,
 			       struct dm_table *t);
 
 /*
+ * Table keyslot manager functions
+ */
+void dm_destroy_keyslot_manager(struct blk_keyslot_manager *ksm);
+
+/*
  * A wrapper around vmalloc.
  */
 void *dm_vcalloc(unsigned long nmemb, unsigned long elem_size);