[RFC PATCH v6 2/4] blk-crypto: show supported key types in sysfs

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

Add sysfs files that indicate which type(s) of keys are supported by the
inline encryption hardware associated with a particular request queue:

	/sys/block/$disk/queue/crypto/hw_wrapped_keys
	/sys/block/$disk/queue/crypto/standard_keys

Userspace can use the presence or absence of these files to decide what
encyption settings to use.

Don't use a single key_type file, as devices might support both key
types at the same time.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 Documentation/ABI/stable/sysfs-block | 18 ++++++++++++++
 block/blk-crypto-sysfs.c             | 35 ++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index cd14ecb3c9a5..ab0a36a342d5 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -166,6 +166,16 @@ Description:
 		encryption, refer to Documentation/block/inline-encryption.rst.
 
 
+What:		/sys/block/<disk>/queue/crypto/hw_wrapped_keys
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] The presence of this file indicates that the device
+		supports hardware-wrapped inline encryption keys, i.e. key blobs
+		that can only be unwrapped and used by dedicated hardware.  For
+		more information about hardware-wrapped inline encryption keys,
+		see Documentation/block/inline-encryption.rst.
+
+
 What:		/sys/block/<disk>/queue/crypto/max_dun_bits
 Date:		February 2022
 Contact:	linux-block@vger.kernel.org
@@ -204,6 +214,14 @@ Description:
 		use with inline encryption.
 
 
+What:		/sys/block/<disk>/queue/crypto/standard_keys
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] The presence of this file indicates that the device
+		supports standard inline encryption keys, i.e. keys that are
+		managed in raw, plaintext form in software.
+
+
 What:		/sys/block/<disk>/queue/dax
 Date:		June 2016
 Contact:	linux-block@vger.kernel.org
diff --git a/block/blk-crypto-sysfs.c b/block/blk-crypto-sysfs.c
index fd93bd2f33b7..d1dbe50f806a 100644
--- a/block/blk-crypto-sysfs.c
+++ b/block/blk-crypto-sysfs.c
@@ -31,6 +31,13 @@ static struct blk_crypto_attr *attr_to_crypto_attr(struct attribute *attr)
 	return container_of(attr, struct blk_crypto_attr, attr);
 }
 
+static ssize_t hw_wrapped_keys_show(struct blk_crypto_profile *profile,
+				    struct blk_crypto_attr *attr, char *page)
+{
+	/* Always show supported, since the file doesn't exist otherwise. */
+	return sysfs_emit(page, "supported\n");
+}
+
 static ssize_t max_dun_bits_show(struct blk_crypto_profile *profile,
 				 struct blk_crypto_attr *attr, char *page)
 {
@@ -43,20 +50,48 @@ static ssize_t num_keyslots_show(struct blk_crypto_profile *profile,
 	return sysfs_emit(page, "%u\n", profile->num_slots);
 }
 
+static ssize_t standard_keys_show(struct blk_crypto_profile *profile,
+				  struct blk_crypto_attr *attr, char *page)
+{
+	/* Always show supported, since the file doesn't exist otherwise. */
+	return sysfs_emit(page, "supported\n");
+}
+
 #define BLK_CRYPTO_RO_ATTR(_name) \
 	static struct blk_crypto_attr _name##_attr = __ATTR_RO(_name)
 
+BLK_CRYPTO_RO_ATTR(hw_wrapped_keys);
 BLK_CRYPTO_RO_ATTR(max_dun_bits);
 BLK_CRYPTO_RO_ATTR(num_keyslots);
+BLK_CRYPTO_RO_ATTR(standard_keys);
+
+static umode_t blk_crypto_is_visible(struct kobject *kobj,
+				     struct attribute *attr, int n)
+{
+	struct blk_crypto_profile *profile = kobj_to_crypto_profile(kobj);
+	struct blk_crypto_attr *a = attr_to_crypto_attr(attr);
+
+	if (a == &hw_wrapped_keys_attr &&
+	    !(profile->key_types_supported & BLK_CRYPTO_KEY_TYPE_HW_WRAPPED))
+		return 0;
+	if (a == &standard_keys_attr &&
+	    !(profile->key_types_supported & BLK_CRYPTO_KEY_TYPE_STANDARD))
+		return 0;
+
+	return 0444;
+}
 
 static struct attribute *blk_crypto_attrs[] = {
+	&hw_wrapped_keys_attr.attr,
 	&max_dun_bits_attr.attr,
 	&num_keyslots_attr.attr,
+	&standard_keys_attr.attr,
 	NULL,
 };
 
 static const struct attribute_group blk_crypto_attr_group = {
 	.attrs = blk_crypto_attrs,
+	.is_visible = blk_crypto_is_visible,
 };
 
 /*
-- 
2.37.3