Provide a kernel API to retrieve secrets from the UV secret store.
Add two new functions:
* `uv_get_secret_metadata` - get metadata for a given secret identifier
* `uv_retrieve_secret` - get the secret value for the secret index

With those two functions one can extract the secret for a given secret
id, if the secret is retrievable.

Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
---
 arch/s390/include/asm/uv.h | 136 ++++++++++++++++++++++++++++++++++++-
 arch/s390/kernel/uv.c      | 129 ++++++++++++++++++++++++++++++++++-
 2 files changed, 262 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
index 94ff58336e8e..f063e21d898d 100644
--- a/arch/s390/include/asm/uv.h
+++ b/arch/s390/include/asm/uv.h
@@ -2,7 +2,7 @@
 /*
  * Ultravisor Interfaces
  *
- * Copyright IBM Corp. 2019, 2022
+ * Copyright IBM Corp. 2019, 2024
  *
  * Author(s):
  *	Vasily Gorbik <gor@linux.ibm.com>
@@ -62,6 +62,7 @@
 #define UVC_CMD_ADD_SECRET		0x1031
 #define UVC_CMD_LIST_SECRETS		0x1033
 #define UVC_CMD_LOCK_SECRETS		0x1034
+#define UVC_CMD_RETR_SECRET		0x1035
 
 /* Bits in installed uv calls */
 enum uv_cmds_inst {
@@ -95,6 +96,7 @@ enum uv_cmds_inst {
 	BIT_UVC_CMD_ADD_SECRET = 29,
 	BIT_UVC_CMD_LIST_SECRETS = 30,
 	BIT_UVC_CMD_LOCK_SECRETS = 31,
+	BIT_UVC_CMD_RETR_SECRET = 33,
 };
 
 enum uv_feat_ind {
@@ -318,7 +320,6 @@ struct uv_cb_dump_complete {
  * A common UV call struct for pv guests that contains a single address
  * Examples:
  * Add Secret
- * List Secrets
  */
 struct uv_cb_guest_addr {
 	struct uv_cb_header header;
@@ -327,6 +328,91 @@ struct uv_cb_guest_addr {
 	u64 reserved28[4];
 } __packed __aligned(8);
 
+#define UVC_RC_RETR_SECR_BUF_SMALL	0x0109
+#define UVC_RC_RETR_SECR_STORE_EMPTY	0x010f
+#define UVC_RC_RETR_SECR_INV_IDX	0x0110
+#define UVC_RC_RETR_SECR_INV_SECRET	0x0111
+
+struct uv_cb_retr_secr {
+	struct uv_cb_header header;
+	u64 reserved08[2];
+	u16 secret_idx;
+	u16 reserved1a;
+	u32 buf_size;
+	u64 buf_addr;
+	u64 reserved28[4];
+}  __packed __aligned(8);
+
+struct uv_cb_list_secrets {
+	struct uv_cb_header header;
+	u64 reserved08[2];
+	u8  reserved18[6];
+	u16 start_idx;
+	u64 list_addr;
+	u64 reserved28[4];
+} __packed __aligned(8);
+
+enum uv_secret_types {
+	UV_SECRET_INVAL = 0x0,
+	UV_SECRET_NULL = 0x1,
+	UV_SECRET_ASSOCIATION = 0x2,
+	UV_SECRET_PLAIN = 0x3,
+	UV_SECRET_AES_128 = 0x4,
+	UV_SECRET_AES_192 = 0x5,
+	UV_SECRET_AES_256 = 0x6,
+	UV_SECRET_AES_XTS_128 = 0x7,
+	UV_SECRET_AES_XTS_256 = 0x8,
+	UV_SECRET_HMAC_SHA_256 = 0x9,
+	UV_SECRET_HMAC_SHA_512 = 0xa,
+	/* 0x0b - 0x10 reserved */
+	UV_SECRET_ECDSA_P256 = 0x11,
+	UV_SECRET_ECDSA_P384 = 0x12,
+	UV_SECRET_ECDSA_P521 = 0x13,
+	UV_SECRET_ECDSA_ED25519 = 0x14,
+	UV_SECRET_ECDSA_ED448 = 0x15,
+};
+
+/**
+ * uv_secret_list_item_hdr - UV secret metadata.
+ * @index: Index of the secret in the secret list.
+ * @type: Type of the secret. See `enum uv_secret_types`.
+ * @length: Length of the stored secret.
+ */
+struct uv_secret_list_item_hdr {
+	u16 index;
+	u16 type;
+	u32 length;
+} __packed __aligned(8);
+
+#define UV_SECRET_ID_LEN 32
+/**
+ * uv_secret_list_item - UV secret entry.
+ * @hdr: The metadata of this secret.
+ * @id: The ID of this secret, not the secret itself.
+ */
+struct uv_secret_list_item {
+	struct uv_secret_list_item_hdr hdr;
+	u64 reserverd08;
+	u8 id[UV_SECRET_ID_LEN];
+} __packed __aligned(8);
+
+/**
+ * uv_secret_list - UV secret-metadata list.
+ * @num_secr_stored: Number of secrets stored in this list.
+ * @total_num_secrets: Number of secrets stored in the UV for this guest.
+ * @next_secret_idx: positive number if there are more secrets available or zero.
+ * @secrets: Up to 85 UV-secret metadata entries.
+ */
+struct uv_secret_list {
+	u16 num_secr_stored;
+	u16 total_num_secrets;
+	u16 next_secret_idx;
+	u16 reserved_06;
+	u64 reserved_08;
+	struct uv_secret_list_item secrets[85];
+} __packed __aligned(8);
+static_assert(sizeof(struct uv_secret_list) == PAGE_SIZE);
+
 static inline int __uv_call(unsigned long r1, unsigned long r2)
 {
 	int cc;
@@ -383,6 +469,48 @@ static inline int uv_cmd_nodata(u64 handle, u16 cmd, u16 *rc, u16 *rrc)
 	return cc ? -EINVAL : 0;
 }
 
+/**
+ *  uv_list_secrets() - Do a List Secrets UVC.
+ *
+ *  @buf: Buffer to write list into; size of one page.
+ *  @start_idx: The smallest index that should be included in the list.
+ *		For the fist invocation use 0.
+ *  @rc: Pointer to store the return code or NULL.
+ *  @rrc: Pointer to store the return reason code or NULL.
+ *
+ *  This function calls the List Secrets UVC. The result is written into `buf`,
+ *  that needs to be at least one page of writable memory.
+ *  `buf` consists of:
+ *  * %struct uv_secret_list_hdr
+ *  * %struct uv_secret_list_item (multiple)
+ *
+ *  For `start_idx` use _0_ for the first call. If there are more secrets available
+ *  but could not fit into the page then `rc` is `UVC_RC_MORE_DATA`.
+ *  In this case use `uv_secret_list_hdr.next_secret_idx` for `start_idx`.
+ *
+ *  Context: might sleep.
+ *
+ *  Return: The UVC condition code.
+ */
+static inline int uv_list_secrets(struct uv_secret_list *buf, u16 start_idx,
+				  u16 *rc, u16 *rrc)
+{
+	struct uv_cb_list_secrets uvcb = {
+		.header.len = sizeof(uvcb),
+		.header.cmd = UVC_CMD_LIST_SECRETS,
+		.start_idx = start_idx,
+		.list_addr = (u64)buf,
+	};
+	int cc = uv_call_sched(0, (u64)&uvcb);
+
+	if (rc)
+		*rc = uvcb.header.rc;
+	if (rrc)
+		*rrc = uvcb.header.rrc;
+
+	return cc;
+}
+
 struct uv_info {
 	unsigned long inst_calls_list[4];
 	unsigned long uv_base_stor_len;
@@ -469,6 +597,10 @@ static inline int uv_remove_shared(unsigned long addr)
 	return share(addr, UVC_CMD_REMOVE_SHARED_ACCESS);
 }
 
+int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
+			   struct uv_secret_list_item_hdr *secret);
+int uv_retrieve_secret(u16 secret_idx, u8 *buf, size_t buf_size);
+
 extern int prot_virt_host;
 
 static inline int is_prot_virt_host(void)
diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9646f773208a..cb9cb3f47471 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -2,7 +2,7 @@
 /*
  * Common Ultravisor functions and initialization
  *
- * Copyright IBM Corp. 2019, 2020
+ * Copyright IBM Corp. 2019, 2024
  */
 #define KMSG_COMPONENT "prot_virt"
 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
@@ -787,3 +787,130 @@ static int __init uv_info_init(void)
 	return rc;
 }
 device_initcall(uv_info_init);
+
+/*
+ * Find the secret with the secret_id in the provided list.
+ *
+ * Context: might sleep.
+ */
+static int find_secret_in_page(const u8 secret_id[UV_SECRET_ID_LEN],
+			       const struct uv_secret_list *list,
+			       struct uv_secret_list_item_hdr *secret)
+{
+	u16 i;
+
+	for (i = 0; i < list->total_num_secrets; i++) {
+		if (memcmp(secret_id, list->secrets[i].id, UV_SECRET_ID_LEN) == 0) {
+			*secret = list->secrets[i].hdr;
+			return 0;
+		}
+	}
+	return -ENOENT;
+}
+
+/*
+ * Do the actual search for `uv_get_secret_metadata`.
+ *
+ * Context: might sleep.
+ */
+static int find_secret(const u8 secret_id[UV_SECRET_ID_LEN],
+		       struct uv_secret_list *list,
+		       struct uv_secret_list_item_hdr *secret)
+{
+	u16 start_idx = 0;
+	u16 list_rc;
+	int ret;
+
+	do {
+		uv_list_secrets(list, start_idx, &list_rc, NULL);
+		if (list_rc != UVC_RC_EXECUTED && list_rc != UVC_RC_MORE_DATA) {
+			if (list_rc == UVC_RC_INV_CMD)
+				return -ENODEV;
+			else
+				return -EIO;
+		}
+		ret = find_secret_in_page(secret_id, list, secret);
+		if (ret == 0)
+			return ret;
+		start_idx = list->next_secret_idx;
+	} while (list_rc == UVC_RC_MORE_DATA && start_idx < list->next_secret_idx);
+
+	return -ENOENT;
+}
+
+/**
+ * uv_get_secret_metadata() - get secret metadata for a given secret id.
+ * @secret_id: search pattern.
+ * @secret: output data, containing the secret's metadata.
+ *
+ * Search for a secret with the given secret_id in the Ultravisor secret store.
+ *
+ * Context: might sleep.
+ *
+ * Return:
+ * * %0:	- Found entry; secret->idx and secret->type are valid.
+ * * %ENOENT	- No entry found.
+ * * %ENODEV:	- Not supported: UV not available or command not available.
+ * * %EIO:	- Other unexpected UV error.
+ */
+int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
+			   struct uv_secret_list_item_hdr *secret)
+{
+	struct uv_secret_list *buf;
+	int rc;
+
+	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+	rc = find_secret(secret_id, buf, secret);
+	kfree(buf);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(uv_get_secret_metadata);
+
+/**
+ * uv_retrieve_secret() - get the secret value for the secret index.
+ * @secret_idx: Secret index for which the secret should be retrieved.
+ * @buf: Buffer to store retrieved secret.
+ * @buf_size: Size of the buffer. The correct buffer size is reported as part of
+ * the result from `uv_get_secret_metadata`.
+ *
+ * Calls the Retrieve Secret UVC and translates the UV return code into an errno.
+ *
+ * Context: might sleep.
+ *
+ * Return:
+ * * %0		- Entry found; buffer contains a valid secret.
+ * * %ENOENT:	- No entry found or secret at the index is non-retrievable.
+ * * %ENODEV:	- Not supported: UV not available or command not available.
+ * * %EINVAL:	- Buffer too small for content.
+ * * %EIO:	- Other unexpected UV error.
+ */
+int uv_retrieve_secret(u16 secret_idx, u8 *buf, size_t buf_size)
+{
+	struct uv_cb_retr_secr uvcb = {
+		.header.len = sizeof(uvcb),
+		.header.cmd = UVC_CMD_RETR_SECRET,
+		.secret_idx = secret_idx,
+		.buf_addr = (u64)buf,
+		.buf_size = buf_size,
+	};
+
+	uv_call_sched(0, (u64)&uvcb);
+
+	switch (uvcb.header.rc) {
+	case UVC_RC_EXECUTED:
+		return 0;
+	case UVC_RC_INV_CMD:
+		return -ENODEV;
+	case UVC_RC_RETR_SECR_STORE_EMPTY:
+	case UVC_RC_RETR_SECR_INV_SECRET:
+	case UVC_RC_RETR_SECR_INV_IDX:
+		return -ENOENT;
+	case UVC_RC_RETR_SECR_BUF_SMALL:
+		return -EINVAL;
+	default:
+		return -EIO;
+	}
+}
+EXPORT_SYMBOL_GPL(uv_retrieve_secret);
-- 
2.45.2

Provide a kernel API to retrieve secrets from the UV secret store.
Add two new functions:
* `uv_get_secret_metadata` - get metadata for a given secret identifier
* `uv_retrieve_secret` - get the secret value for the secret index

With those two functions one can extract the secret for a given secret
id, if the secret is retrievable.

Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
---
Resend this patch rebased onto my other series
's390/uv: Provide host-key hashes in sysfs'

see: https://lore.kernel.org/lkml/20241015113940.3088249-1-seiden@linux.ibm.com/

 arch/s390/include/asm/uv.h | 136 ++++++++++++++++++++++++++++++++++++-
 arch/s390/kernel/uv.c      | 129 ++++++++++++++++++++++++++++++++++-
 2 files changed, 262 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
index 49ca54827379..729b1e057784 100644
--- a/arch/s390/include/asm/uv.h
+++ b/arch/s390/include/asm/uv.h
@@ -2,7 +2,7 @@
 /*
  * Ultravisor Interfaces
  *
- * Copyright IBM Corp. 2019, 2022
+ * Copyright IBM Corp. 2019, 2024
  *
  * Author(s):
  *	Vasily Gorbik <gor@linux.ibm.com>
@@ -63,6 +63,7 @@
 #define UVC_CMD_ADD_SECRET		0x1031
 #define UVC_CMD_LIST_SECRETS		0x1033
 #define UVC_CMD_LOCK_SECRETS		0x1034
+#define UVC_CMD_RETR_SECRET		0x1035
 
 /* Bits in installed uv calls */
 enum uv_cmds_inst {
@@ -96,6 +97,7 @@ enum uv_cmds_inst {
 	BIT_UVC_CMD_ADD_SECRET = 29,
 	BIT_UVC_CMD_LIST_SECRETS = 30,
 	BIT_UVC_CMD_LOCK_SECRETS = 31,
+	BIT_UVC_CMD_RETR_SECRET = 33,
 	BIT_UVC_CMD_QUERY_KEYS = 34,
 };
 
@@ -335,7 +337,6 @@ struct uv_cb_dump_complete {
  * A common UV call struct for pv guests that contains a single address
  * Examples:
  * Add Secret
- * List Secrets
  */
 struct uv_cb_guest_addr {
 	struct uv_cb_header header;
@@ -344,6 +345,91 @@ struct uv_cb_guest_addr {
 	u64 reserved28[4];
 } __packed __aligned(8);
 
+#define UVC_RC_RETR_SECR_BUF_SMALL	0x0109
+#define UVC_RC_RETR_SECR_STORE_EMPTY	0x010f
+#define UVC_RC_RETR_SECR_INV_IDX	0x0110
+#define UVC_RC_RETR_SECR_INV_SECRET	0x0111
+
+struct uv_cb_retr_secr {
+	struct uv_cb_header header;
+	u64 reserved08[2];
+	u16 secret_idx;
+	u16 reserved1a;
+	u32 buf_size;
+	u64 buf_addr;
+	u64 reserved28[4];
+}  __packed __aligned(8);
+
+struct uv_cb_list_secrets {
+	struct uv_cb_header header;
+	u64 reserved08[2];
+	u8  reserved18[6];
+	u16 start_idx;
+	u64 list_addr;
+	u64 reserved28[4];
+} __packed __aligned(8);
+
+enum uv_secret_types {
+	UV_SECRET_INVAL = 0x0,
+	UV_SECRET_NULL = 0x1,
+	UV_SECRET_ASSOCIATION = 0x2,
+	UV_SECRET_PLAIN = 0x3,
+	UV_SECRET_AES_128 = 0x4,
+	UV_SECRET_AES_192 = 0x5,
+	UV_SECRET_AES_256 = 0x6,
+	UV_SECRET_AES_XTS_128 = 0x7,
+	UV_SECRET_AES_XTS_256 = 0x8,
+	UV_SECRET_HMAC_SHA_256 = 0x9,
+	UV_SECRET_HMAC_SHA_512 = 0xa,
+	/* 0x0b - 0x10 reserved */
+	UV_SECRET_ECDSA_P256 = 0x11,
+	UV_SECRET_ECDSA_P384 = 0x12,
+	UV_SECRET_ECDSA_P521 = 0x13,
+	UV_SECRET_ECDSA_ED25519 = 0x14,
+	UV_SECRET_ECDSA_ED448 = 0x15,
+};
+
+/**
+ * uv_secret_list_item_hdr - UV secret metadata.
+ * @index: Index of the secret in the secret list.
+ * @type: Type of the secret. See `enum uv_secret_types`.
+ * @length: Length of the stored secret.
+ */
+struct uv_secret_list_item_hdr {
+	u16 index;
+	u16 type;
+	u32 length;
+} __packed __aligned(8);
+
+#define UV_SECRET_ID_LEN 32
+/**
+ * uv_secret_list_item - UV secret entry.
+ * @hdr: The metadata of this secret.
+ * @id: The ID of this secret, not the secret itself.
+ */
+struct uv_secret_list_item {
+	struct uv_secret_list_item_hdr hdr;
+	u64 reserverd08;
+	u8 id[UV_SECRET_ID_LEN];
+} __packed __aligned(8);
+
+/**
+ * uv_secret_list - UV secret-metadata list.
+ * @num_secr_stored: Number of secrets stored in this list.
+ * @total_num_secrets: Number of secrets stored in the UV for this guest.
+ * @next_secret_idx: positive number if there are more secrets available or zero.
+ * @secrets: Up to 85 UV-secret metadata entries.
+ */
+struct uv_secret_list {
+	u16 num_secr_stored;
+	u16 total_num_secrets;
+	u16 next_secret_idx;
+	u16 reserved_06;
+	u64 reserved_08;
+	struct uv_secret_list_item secrets[85];
+} __packed __aligned(8);
+static_assert(sizeof(struct uv_secret_list) == PAGE_SIZE);
+
 static inline int __uv_call(unsigned long r1, unsigned long r2)
 {
 	int cc;
@@ -400,6 +486,48 @@ static inline int uv_cmd_nodata(u64 handle, u16 cmd, u16 *rc, u16 *rrc)
 	return cc ? -EINVAL : 0;
 }
 
+/**
+ *  uv_list_secrets() - Do a List Secrets UVC.
+ *
+ *  @buf: Buffer to write list into; size of one page.
+ *  @start_idx: The smallest index that should be included in the list.
+ *		For the fist invocation use 0.
+ *  @rc: Pointer to store the return code or NULL.
+ *  @rrc: Pointer to store the return reason code or NULL.
+ *
+ *  This function calls the List Secrets UVC. The result is written into `buf`,
+ *  that needs to be at least one page of writable memory.
+ *  `buf` consists of:
+ *  * %struct uv_secret_list_hdr
+ *  * %struct uv_secret_list_item (multiple)
+ *
+ *  For `start_idx` use _0_ for the first call. If there are more secrets available
+ *  but could not fit into the page then `rc` is `UVC_RC_MORE_DATA`.
+ *  In this case use `uv_secret_list_hdr.next_secret_idx` for `start_idx`.
+ *
+ *  Context: might sleep.
+ *
+ *  Return: The UVC condition code.
+ */
+static inline int uv_list_secrets(struct uv_secret_list *buf, u16 start_idx,
+				  u16 *rc, u16 *rrc)
+{
+	struct uv_cb_list_secrets uvcb = {
+		.header.len = sizeof(uvcb),
+		.header.cmd = UVC_CMD_LIST_SECRETS,
+		.start_idx = start_idx,
+		.list_addr = (u64)buf,
+	};
+	int cc = uv_call_sched(0, (u64)&uvcb);
+
+	if (rc)
+		*rc = uvcb.header.rc;
+	if (rrc)
+		*rrc = uvcb.header.rrc;
+
+	return cc;
+}
+
 struct uv_info {
 	unsigned long inst_calls_list[4];
 	unsigned long uv_base_stor_len;
@@ -486,6 +614,10 @@ static inline int uv_remove_shared(unsigned long addr)
 	return share(addr, UVC_CMD_REMOVE_SHARED_ACCESS);
 }
 
+int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
+			   struct uv_secret_list_item_hdr *secret);
+int uv_retrieve_secret(u16 secret_idx, u8 *buf, size_t buf_size);
+
 extern int prot_virt_host;
 
 static inline int is_prot_virt_host(void)
diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 3c74e6179cdc..4fbe63f59ebd 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -2,7 +2,7 @@
 /*
  * Common Ultravisor functions and initialization
  *
- * Copyright IBM Corp. 2019, 2020
+ * Copyright IBM Corp. 2019, 2024
  */
 #define KMSG_COMPONENT "prot_virt"
 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
@@ -870,3 +870,130 @@ static int __init uv_sysfs_init(void)
 	return rc;
 }
 device_initcall(uv_sysfs_init);
+
+/*
+ * Find the secret with the secret_id in the provided list.
+ *
+ * Context: might sleep.
+ */
+static int find_secret_in_page(const u8 secret_id[UV_SECRET_ID_LEN],
+			       const struct uv_secret_list *list,
+			       struct uv_secret_list_item_hdr *secret)
+{
+	u16 i;
+
+	for (i = 0; i < list->total_num_secrets; i++) {
+		if (memcmp(secret_id, list->secrets[i].id, UV_SECRET_ID_LEN) == 0) {
+			*secret = list->secrets[i].hdr;
+			return 0;
+		}
+	}
+	return -ENOENT;
+}
+
+/*
+ * Do the actual search for `uv_get_secret_metadata`.
+ *
+ * Context: might sleep.
+ */
+static int find_secret(const u8 secret_id[UV_SECRET_ID_LEN],
+		       struct uv_secret_list *list,
+		       struct uv_secret_list_item_hdr *secret)
+{
+	u16 start_idx = 0;
+	u16 list_rc;
+	int ret;
+
+	do {
+		uv_list_secrets(list, start_idx, &list_rc, NULL);
+		if (list_rc != UVC_RC_EXECUTED && list_rc != UVC_RC_MORE_DATA) {
+			if (list_rc == UVC_RC_INV_CMD)
+				return -ENODEV;
+			else
+				return -EIO;
+		}
+		ret = find_secret_in_page(secret_id, list, secret);
+		if (ret == 0)
+			return ret;
+		start_idx = list->next_secret_idx;
+	} while (list_rc == UVC_RC_MORE_DATA && start_idx < list->next_secret_idx);
+
+	return -ENOENT;
+}
+
+/**
+ * uv_get_secret_metadata() - get secret metadata for a given secret id.
+ * @secret_id: search pattern.
+ * @secret: output data, containing the secret's metadata.
+ *
+ * Search for a secret with the given secret_id in the Ultravisor secret store.
+ *
+ * Context: might sleep.
+ *
+ * Return:
+ * * %0:	- Found entry; secret->idx and secret->type are valid.
+ * * %ENOENT	- No entry found.
+ * * %ENODEV:	- Not supported: UV not available or command not available.
+ * * %EIO:	- Other unexpected UV error.
+ */
+int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
+			   struct uv_secret_list_item_hdr *secret)
+{
+	struct uv_secret_list *buf;
+	int rc;
+
+	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+	rc = find_secret(secret_id, buf, secret);
+	kfree(buf);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(uv_get_secret_metadata);
+
+/**
+ * uv_retrieve_secret() - get the secret value for the secret index.
+ * @secret_idx: Secret index for which the secret should be retrieved.
+ * @buf: Buffer to store retrieved secret.
+ * @buf_size: Size of the buffer. The correct buffer size is reported as part of
+ * the result from `uv_get_secret_metadata`.
+ *
+ * Calls the Retrieve Secret UVC and translates the UV return code into an errno.
+ *
+ * Context: might sleep.
+ *
+ * Return:
+ * * %0		- Entry found; buffer contains a valid secret.
+ * * %ENOENT:	- No entry found or secret at the index is non-retrievable.
+ * * %ENODEV:	- Not supported: UV not available or command not available.
+ * * %EINVAL:	- Buffer too small for content.
+ * * %EIO:	- Other unexpected UV error.
+ */
+int uv_retrieve_secret(u16 secret_idx, u8 *buf, size_t buf_size)
+{
+	struct uv_cb_retr_secr uvcb = {
+		.header.len = sizeof(uvcb),
+		.header.cmd = UVC_CMD_RETR_SECRET,
+		.secret_idx = secret_idx,
+		.buf_addr = (u64)buf,
+		.buf_size = buf_size,
+	};
+
+	uv_call_sched(0, (u64)&uvcb);
+
+	switch (uvcb.header.rc) {
+	case UVC_RC_EXECUTED:
+		return 0;
+	case UVC_RC_INV_CMD:
+		return -ENODEV;
+	case UVC_RC_RETR_SECR_STORE_EMPTY:
+	case UVC_RC_RETR_SECR_INV_SECRET:
+	case UVC_RC_RETR_SECR_INV_IDX:
+		return -ENOENT;
+	case UVC_RC_RETR_SECR_BUF_SMALL:
+		return -EINVAL;
+	default:
+		return -EIO;
+	}
+}
+EXPORT_SYMBOL_GPL(uv_retrieve_secret);
-- 
2.45.2