[PATCHv2 57/59] x86/mktme: Document the MKTME Key Service API

["Kirill A. Shutemov" <kirill@shutemov.name>]

From: Alison Schofield <alison.schofield@intel.com>

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 Documentation/x86/mktme/index.rst      |  1 +
 Documentation/x86/mktme/mktme_keys.rst | 61 ++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 Documentation/x86/mktme/mktme_keys.rst

diff --git a/Documentation/x86/mktme/index.rst b/Documentation/x86/mktme/index.rst
index 0f021cc4a2db..8cf2b7d62091 100644
--- a/Documentation/x86/mktme/index.rst
+++ b/Documentation/x86/mktme/index.rst
@@ -8,3 +8,4 @@ Multi-Key Total Memory Encryption (MKTME)
    mktme_overview
    mktme_mitigations
    mktme_configuration
+   mktme_keys
diff --git a/Documentation/x86/mktme/mktme_keys.rst b/Documentation/x86/mktme/mktme_keys.rst
new file mode 100644
index 000000000000..5d9125eb7950
--- /dev/null
+++ b/Documentation/x86/mktme/mktme_keys.rst
@@ -0,0 +1,61 @@
+MKTME Key Service API
+==========+MKTME is a new key service type added to the Linux Kernel Key Service.
+
+The MKTME Key Service type is available when CONFIG_X86_INTEL_MKTME is
+turned on in Intel platforms that support the MKTME feature.
+
+The MKTME Key Service type manages the allocation of hardware encryption
+keys. Users can request an MKTME type key and then use that key to
+encrypt memory with the encrypt_mprotect() system call.
+
+Usage
+-----
+    When using the Kernel Key Service to request an *mktme* key,
+    specify the *payload* as follows:
+
+    type+        *cpu*	User requests a CPU generated encryption key.
+                The CPU generates and assigns an ephemeral key.
+
+        *no-encrypt*
+                 User requests that hardware does not encrypt
+                 memory when this key is in use.
+
+    algorithm+        When type=cpu the algorithm field must be *aes-xts-128*
+        *aes-xts-128* is the only supported encryption algorithm
+
+        When type=no-encrypt the algorithm field must not be
+        present in the payload.
+
+ERRORS
+------
+    In addition to the Errors returned from the Kernel Key Service,
+    add_key(2) or keyctl(1) commands, the MKTME Key Service type may
+    return the following errors:
+
+    EINVAL for any payload specification that does not match the
+           MKTME type payload as defined above.
+
+    EACCES for access denied. The MKTME key type uses capabilities
+           to restrict the allocation of keys to privileged users.
+           CAP_SYS_RESOURCE is required, but it will accept the
+           broader capability of CAP_SYS_ADMIN. See capabilities(7).
+
+    ENOKEY if a hardware key cannot be allocated. Additional error
+           messages will describe the hardware programming errors.
+
+EXAMPLES
+--------
+    Add a 'cpu' type key::
+
+        char \*options_CPU = "type=cpu algorithmŪs-xts-128";
+
+        key = add_key("mktme", "name", options_CPU, strlen(options_CPU),
+                      KEY_SPEC_THREAD_KEYRING);
+
+    Add a "no-encrypt' type key::
+
+	key = add_key("mktme", "name", "no-encrypt", strlen(options_CPU),
+		      KEY_SPEC_THREAD_KEYRING);
-- 
2.21.0