blk-crypto: add ioctls to create and prepare hardware-wrapped keys

Until this point, the kernel can use hardware-wrapped keys to do
encryption if userspace provides one -- specifically a key in
ephemerally-wrapped form.  However, no generic way has been provided for
userspace to get such a key in the first place.

Getting such a key is a two-step process.  First, the key needs to be
imported from a raw key or generated by the hardware, producing a key in
long-term wrapped form.  This happens once in the whole lifetime of the
key.  Second, the long-term wrapped key needs to be converted into
ephemerally-wrapped form.  This happens each time the key is "unlocked".

In Android, these operations are supported in a generic way through
KeyMint, a userspace abstraction layer.  However, that method is
Android-specific and can't be used on other Linux systems, may rely on
proprietary libraries, and also misleads people into supporting KeyMint
features like rollback resistance that make sense for other KeyMint keys
but don't make sense for hardware-wrapped inline encryption keys.

Therefore, this patch provides a generic kernel interface for these
operations by introducing new block device ioctls:

- BLKCRYPTOIMPORTKEY: convert a raw key to long-term wrapped form.

- BLKCRYPTOGENERATEKEY: have the hardware generate a new key, then
  return it in long-term wrapped form.

- BLKCRYPTOPREPAREKEY: convert a key from long-term wrapped form to
  ephemerally-wrapped form.

These ioctls are implemented using new operations in blk_crypto_ll_ops.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Tested-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> # sm8650
Link: https://lore.kernel.org/r/20250204060041.409950-4-ebiggers@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

4 files changed, 100 insertions, 4 deletions

diff --git a/include/linux/blk-crypto-profile.h b/include/linux/blk-crypto-profile.h
index 7764b4f7b45b..4f39e9cd7576 100644
--- a/include/linux/blk-crypto-profile.h
+++ b/include/linux/blk-crypto-profile.h
@@ -71,6 +71,48 @@ struct blk_crypto_ll_ops {
 	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]);
+
+	/**
+	 * @import_key: Create a hardware-wrapped key by importing a raw key.
+	 *
+	 * This only needs to be implemented if BLK_CRYPTO_KEY_TYPE_HW_WRAPPED
+	 * is supported.
+	 *
+	 * On success, must write the new key in long-term wrapped form to
+	 * @lt_key and return its size in bytes.  On failure, must return a
+	 * -errno value.
+	 */
+	int (*import_key)(struct blk_crypto_profile *profile,
+			  const u8 *raw_key, size_t raw_key_size,
+			  u8 lt_key[BLK_CRYPTO_MAX_HW_WRAPPED_KEY_SIZE]);
+
+	/**
+	 * @generate_key: Generate a hardware-wrapped key.
+	 *
+	 * This only needs to be implemented if BLK_CRYPTO_KEY_TYPE_HW_WRAPPED
+	 * is supported.
+	 *
+	 * On success, must write the new key in long-term wrapped form to
+	 * @lt_key and return its size in bytes.  On failure, must return a
+	 * -errno value.
+	 */
+	int (*generate_key)(struct blk_crypto_profile *profile,
+			    u8 lt_key[BLK_CRYPTO_MAX_HW_WRAPPED_KEY_SIZE]);
+
+	/**
+	 * @prepare_key: Prepare a hardware-wrapped key to be used.
+	 *
+	 * Prepare a hardware-wrapped key to be used by converting it from
+	 * long-term wrapped form to ephemerally-wrapped form.  This only needs
+	 * to be implemented if BLK_CRYPTO_KEY_TYPE_HW_WRAPPED is supported.
+	 *
+	 * On success, must write the key in ephemerally-wrapped form to
+	 * @eph_key and return its size in bytes.  On failure, must return
+	 * -EBADMSG if the key is invalid, or another -errno on other error.
+	 */
+	int (*prepare_key)(struct blk_crypto_profile *profile,
+			   const u8 *lt_key, size_t lt_key_size,
+			   u8 eph_key[BLK_CRYPTO_MAX_HW_WRAPPED_KEY_SIZE]);
 };
 
 /**
@@ -163,6 +205,17 @@ void blk_crypto_reprogram_all_keys(struct blk_crypto_profile *profile);
 
 void blk_crypto_profile_destroy(struct blk_crypto_profile *profile);
 
+int blk_crypto_import_key(struct blk_crypto_profile *profile,
+			  const u8 *raw_key, size_t raw_key_size,
+			  u8 lt_key[BLK_CRYPTO_MAX_HW_WRAPPED_KEY_SIZE]);
+
+int blk_crypto_generate_key(struct blk_crypto_profile *profile,
+			    u8 lt_key[BLK_CRYPTO_MAX_HW_WRAPPED_KEY_SIZE]);
+
+int blk_crypto_prepare_key(struct blk_crypto_profile *profile,
+			   const u8 *lt_key, size_t lt_key_size,
+			   u8 eph_key[BLK_CRYPTO_MAX_HW_WRAPPED_KEY_SIZE]);
+
 void blk_crypto_intersect_capabilities(struct blk_crypto_profile *parent,
 				       const struct blk_crypto_profile *child);
 
diff --git a/include/linux/blk-crypto.h b/include/linux/blk-crypto.h
index 81f932b3ea37..58b0c5254a67 100644
--- a/include/linux/blk-crypto.h
+++ b/include/linux/blk-crypto.h
@@ -8,6 +8,7 @@
 
 #include <linux/minmax.h>
 #include <linux/types.h>
+#include <uapi/linux/blk-crypto.h>
 
 enum blk_crypto_mode_num {
 	BLK_ENCRYPTION_MODE_INVALID,
diff --git a/include/uapi/linux/blk-crypto.h b/include/uapi/linux/blk-crypto.h
new file mode 100644
index 000000000000..97302c6eb6af
--- /dev/null
+++ b/include/uapi/linux/blk-crypto.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_BLK_CRYPTO_H
+#define _UAPI_LINUX_BLK_CRYPTO_H
+
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+struct blk_crypto_import_key_arg {
+	/* Raw key (input) */
+	__u64 raw_key_ptr;
+	__u64 raw_key_size;
+	/* Long-term wrapped key blob (output) */
+	__u64 lt_key_ptr;
+	__u64 lt_key_size;
+	__u64 reserved[4];
+};
+
+struct blk_crypto_generate_key_arg {
+	/* Long-term wrapped key blob (output) */
+	__u64 lt_key_ptr;
+	__u64 lt_key_size;
+	__u64 reserved[4];
+};
+
+struct blk_crypto_prepare_key_arg {
+	/* Long-term wrapped key blob (input) */
+	__u64 lt_key_ptr;
+	__u64 lt_key_size;
+	/* Ephemerally-wrapped key blob (output) */
+	__u64 eph_key_ptr;
+	__u64 eph_key_size;
+	__u64 reserved[4];
+};
+
+/*
+ * These ioctls share the block device ioctl space; see uapi/linux/fs.h.
+ * 140-141 are reserved for future blk-crypto ioctls; any more than that would
+ * require an additional allocation from the block device ioctl space.
+ */
+#define BLKCRYPTOIMPORTKEY _IOWR(0x12, 137, struct blk_crypto_import_key_arg)
+#define BLKCRYPTOGENERATEKEY _IOWR(0x12, 138, struct blk_crypto_generate_key_arg)
+#define BLKCRYPTOPREPAREKEY _IOWR(0x12, 139, struct blk_crypto_prepare_key_arg)
+
+#endif /* _UAPI_LINUX_BLK_CRYPTO_H */
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 2bbe00cf1248..e762e1af650c 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -212,10 +212,8 @@ struct fsxattr {
 #define BLKROTATIONAL _IO(0x12,126)
 #define BLKZEROOUT _IO(0x12,127)
 #define BLKGETDISKSEQ _IOR(0x12,128,__u64)
-/*
- * A jump here: 130-136 are reserved for zoned block devices
- * (see uapi/linux/blkzoned.h)
- */
+/* 130-136 are used by zoned block device ioctls (uapi/linux/blkzoned.h) */
+/* 137-141 are used by blk-crypto ioctls (uapi/linux/blk-crypto.h) */
 
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */