blk-crypto: add basic hardware-wrapped key support

To prevent keys from being compromised if an attacker acquires read
access to kernel memory, some inline encryption hardware can accept keys
which are wrapped by a per-boot hardware-internal key.  This avoids
needing to keep the raw keys in kernel memory, without limiting the
number of keys that can be used.  Such hardware also supports deriving a
"software secret" for cryptographic tasks that can't be handled by
inline encryption; this is needed for fscrypt to work properly.

To support this hardware, allow struct blk_crypto_key to represent a
hardware-wrapped key as an alternative to a raw key, and make drivers
set flags in struct blk_crypto_profile to indicate which types of keys
they support.  Also add the ->derive_sw_secret() low-level operation,
which drivers supporting wrapped keys must implement.

For more information, see the detailed documentation which this patch
adds to Documentation/block/inline-encryption.rst.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Tested-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> # sm8650
Link: https://lore.kernel.org/r/20250204060041.409950-2-ebiggers@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/blk-crypto-profile.h b/include/linux/blk-crypto-profile.h
index 90ab33cb5d0e..7764b4f7b45b 100644
--- a/include/linux/blk-crypto-profile.h
+++ b/include/linux/blk-crypto-profile.h
@@ -57,6 +57,20 @@ struct blk_crypto_ll_ops {
 	int (*keyslot_evict)(struct blk_crypto_profile *profile,
 			     const struct blk_crypto_key *key,
 			     unsigned int slot);
+
+	/**
+	 * @derive_sw_secret: Derive the software secret from a hardware-wrapped
+	 *		      key in ephemerally-wrapped form.
+	 *
+	 * This only needs to be implemented if BLK_CRYPTO_KEY_TYPE_HW_WRAPPED
+	 * is supported.
+	 *
+	 * Must return 0 on success, -EBADMSG if the key is invalid, or another
+	 * -errno code on other errors.
+	 */
+	int (*derive_sw_secret)(struct blk_crypto_profile *profile,
+				const u8 *eph_key, size_t eph_key_size,
+				u8 sw_secret[BLK_CRYPTO_SW_SECRET_SIZE]);
 };
 
 /**
@@ -85,6 +99,12 @@ struct blk_crypto_profile {
 	unsigned int max_dun_bytes_supported;
 
 	/**
+	 * @key_types_supported: A bitmask of the supported key types:
+	 * BLK_CRYPTO_KEY_TYPE_RAW and/or BLK_CRYPTO_KEY_TYPE_HW_WRAPPED.
+	 */
+	unsigned int key_types_supported;
+
+	/**
 	 * @modes_supported: Array of bitmasks that specifies whether each
 	 * combination of crypto mode and data unit size is supported.
 	 * Specifically, the i'th bit of modes_supported[crypto_mode] is set if