doc: add opal secure variable documentation

This patch contains the work-in-progress documentation for the
secure variable design in OPAL. Future revisions of this patch
set will (hopefully) add new pieces of documentation here.

Signed-off-by: Eric Richter <erichte@linux.ibm.com>
[oliver: whitespace error fixes, removed old backend node docs]
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
---
V3:
 - removed metadata
 - removed get_size
 - updated _get semantics for size queries
 - added/expanded device tree properties

V4:
 - updated for new device tree changes

V5:
 - removed incorrect ibm,secureboot changes
 - rewrote bindings using a different format
 - moved secvar documentation under ibm,opal

V6:
 - moved os-secureboot-enforcing to ibm,secureboot
 - removed backend node from secvar node
 - updated documentation on secvar node compatible

doc/device-tree/ibm,opal/secvar/binding.rst

@@ -0,0 +1,169 @@
+secvar Binding
+==============
+
+This device tree binding describes the status of secure variable support,
+including any size values, or values relating to the secure state of the
+system.
+
+
+/ibm,opal/secvar node bindings
+------------------------------
+
+Node: secvar
+
+Description: Container of secvar related properties.
+
+The node name must be "secvar".
+
+It is implemented as a child of the node "/ibm,opal".
+
+The node is optional, will be defined if the platform supports secure
+variables. It will not be created if the system does not.
+
+Properties:
+
+- compatible
+
+  Usage:
+    required
+  Value type:
+    string
+
+  Definition:
+
+  This property defines the compatibility of the current running
+  backend. This defines the binary format of the data buffers passed
+  via the related secvar OPAL API functions. This also defines the
+  expected behavior of how updates should be processed, such as how
+  key updates should be signed, what the key hierarchy is, what
+  algorithms are in use, etc.
+
+  This value also determines how a user can signal a desire to require
+  all further images to require signature validations. See the
+  "On Enforcing Secure Mode" section below.
+
+- status
+
+  Usage:
+    required
+  Value type:
+    string
+
+  Definition:
+
+  This property states the general status of secure variable support. This
+  will be set to "okay" if the secvar OPAL API should be working as expected,
+  and there were no unrecoverable faults in the basic secure variable
+  initialization logic.
+
+  This property may be set to "fail" if the platform does not properly
+  select the drivers to use. Failures may also occur if the storage devices
+  are inaccessible for some reason.
+
+  Failures are NOT caused by malformed data loaded or processed in either
+  storage or backend drivers, as these are faults correctable by a user.
+
+- update-status
+
+  Usage:
+    required
+  Value type:
+    <u64>
+
+  Definition:
+
+  This property should contain the status code of the update processing
+  logic, as returned by the backend. This value is intended to be
+  consumed by userspace tools to confirm updates were processed as
+  intended.
+
+  The value contained in this property should adhere to the table below.
+  Any additional error states that may be specific to a backend should
+  be stored in the backend node.
+
+
+- max-var-size
+
+  Usage:
+    required
+  Value type:
+    <u64>
+
+  Definition:
+
+  This is the maximum buffer size accepted for secure variables. The API
+  will reject updates larger than this value, and storage drivers must
+  reject loading variables larger than this value.
+
+  As this may depend on the persistant storage devices in use, this
+  value is determined by the storage driver, and may differ across
+  platforms.
+
+- max-var-key-len
+
+  Usage:
+    required
+  Value type:
+    <u64>
+
+  Definition:
+
+  This is the maximum size permitted for the key of a variable. As the
+  value is a constant, it should be the same across platforms unless
+  changed in code.
+
+
+Example
+-------
+
+.. code-block:: dts
+
+	/ibm,opal/secvar {
+		compatible = "ibm,edk2-compat-v1";
+
+                status = "okay";
+                max-var-size = <0x1000>;
+                max-var-key-len = <0x400>
+	};
+
+Update Status Code Table
+------------------------
+
+The update status property should be set by the backend driver to a value
+that best fits its error condition. The following table defines the
+general intent of each error code, check backend specific documentation
+for more detail.
+
++-----------------+-----------------------------------------------+
+| update-status   | Generic Reason                                |
++-----------------|-----------------------------------------------+
+| OPAL_SUCCESS    | Updates were found and processed successfully |
++-----------------|-----------------------------------------------+
+| OPAL_EMPTY      | No updates were found, none processed         |
++-----------------|-----------------------------------------------+
+| OPAL_PARAMETER  | Malformed, or unexpected update data blob     |
++-----------------|-----------------------------------------------+
+| OPAL_PERMISSION | Update failed to apply, possible auth failure |
++-----------------|-----------------------------------------------+
+| OPAL_HARDWARE   | Misc. storage-related error                   |
++-----------------|-----------------------------------------------+
+| OPAL_RESOURCE   | Out of space (reported by storage             |
++-----------------|-----------------------------------------------+
+| OPAL_NO_MEM     | Out of memory                                 |
++-----------------+-----------------------------------------------+
+
+
+On Enforcing Secure Mode
+------------------------
+
+The os-secureboot-enforcing property in /ibm,secureboot/ is created by the
+backend if the owner has expressed a desire for boot loaders, kernels, etc
+to require any images to be signed by an appropriate key stored in secure
+variables. As this property is created by the backend, it is up to the
+backend to define what the required state of the secure variables should
+be to enter this mode.
+
+For example, we may want to only enable secure boot if we have a top-
+level "Platform Key", so this property is created by the backend if
+by the end of update processing, a "PK" variable exists. By enrolling a
+PK, the system will be in "secure mode" until the PK is deleted.

doc/device-tree/ibm,secureboot.rst

@@ -33,6 +33,11 @@ Required properties
 
     hw-key-hash-size:   hw-key-hash size
 
+    os-secureboot-enforcing:
+                        this property is created by the secure variable backend
+                        if it detects a desire by the owner to requre any
+                        images (e.g. kernels) to be signed by an appropriate
+                        key stored in secure variables.
 
 Obsolete properties
 -------------------

doc/opal-api/opal-secvar.rst

@@ -0,0 +1,192 @@
+OPAL Secure Variable API
+========================
+
+Overview
+--------
+
+In order to support host OS secure boot on POWER systems, the platform needs
+some form of tamper-resistant persistant storage for authorized public keys.
+Furthermore, these keys must be retrieveable by the host kernel, and new
+keys must be able to be submitted.
+
+OPAL exposes an abstracted "variable" API, in which these keys can be stored
+and retrieved. At a high level, ``opal_secvar_get`` retrieves a specific
+variable corresponding to a particular key. ``opal_secvar_get_next`` can be
+used to iterate through the keys of the stored variables.
+``opal_secvar_enqueue_update`` can be used to submit a new variable for
+processing on next boot.
+
+OPAL_SECVAR_GET
+===============
+::
+
+   #define OPAL_SECVAR_GET                         176
+
+``OPAL_SECVAR_GET`` call retrieves a data blob associated with the supplied
+key.
+
+
+Parameters
+----------
+::
+
+   char     *key
+   uint64_t  key_len
+   void     *data
+   uint64_t *data_size
+
+``key``
+   a buffer used to associate with the variable data. May
+be any encoding, but must not be all zeroes
+
+``key_len``
+   size of the key buffer in bytes
+
+``data``
+   return buffer to store the data blob of the requested variable if
+a match was found. May be set to NULL to only query the size into
+``data_size``
+
+``data_size``
+   reference to the size of the ``data`` buffer. OPAL sets this to
+the size of the requested variable if found.
+
+
+Return Values
+-------------
+
+``OPAL_SUCCESS``
+   the requested data blob was copied successfully. ``data`` was NULL,
+and the ``data_size`` value was set successfully
+
+``OPAL_PARAMETER``
+   ``key`` is NULL.
+   ``key_len`` is zero.
+   ``data_size`` is NULL.
+
+``OPAL_EMPTY``
+   no variable with the supplied ``key`` was found
+
+``OPAL_PARTIAL``
+   the buffer size provided in ``data_size`` was insufficient.
+``data_size`` is set to the minimum required size.
+
+``OPAL_UNSUPPORTED``
+   secure variables are not supported by the platform
+
+``OPAL_RESOURCE``
+   secure variables are supported, but did not initialize properly
+
+OPAL_SECVAR_GET_NEXT
+====================
+::
+
+   #define OPAL_SECVAR_GET_NEXT                        177
+
+``OPAL_SECVAR_GET_NEXT`` returns the key of the next variable in the secure
+variable bank in sequence.
+
+Parameters
+----------
+::
+
+   char     *key
+   uint64_t *key_len
+   uint64_t  key_buf_size
+
+
+``key``
+   name of the previous variable or empty. The key of the next
+variable in sequence will be copied to ``key``. If passed as empty,
+returns the first variable in the bank
+
+``key_len``
+   length in bytes of the key in the  ``key`` buffer. OPAL sets
+this to the length in bytes of the next variable in sequence
+
+``key_buf_size``
+   maximum size of the ``key`` buffer. The next key will not be
+copied if this value is less than the length of the next key
+
+
+Return Values
+-------------
+
+``OPAL_SUCCESS``
+   the key and length of the next variable in sequence was copied
+successfully
+
+``OPAL_PARAMETER``
+   ``key`` or ``key_length`` is NULL.
+   ``key_size`` is zero.
+   ``key_length`` is impossibly large. No variable with the associated
+``key`` was found
+
+``OPAL_EMPTY``
+   end of list reached
+
+``OPAL_PARTIAL``
+   the size specified in ``key_size`` is insufficient for the next
+variable's key length. ``key_length`` is set to the next variable's
+length, but ``key`` is untouched
+
+``OPAL_UNSUPPORTED``
+   secure variables are not supported by the platform
+
+``OPAL_RESOURCE``
+   secure variables are supported, but did not initialize properly
+
+OPAL_SECVAR_ENQUEUE_UPDATE
+==========================
+::
+
+   #define OPAL_SECVAR_ENQUEUE_UPDATE                    178
+
+``OPAL_SECVAR_ENQUEUE`` call appends the supplied variable data to the
+queue for processing on next boot.
+
+Parameters
+----------
+::
+
+   char     *key
+   uint64_t  key_len
+   void     *data
+   uint64_t  data_size
+
+``key``
+   a buffer used to associate with the variable data. May
+be any encoding, but must not be all zeroes
+
+``key_len``
+   size of the key buffer in bytes
+
+``data``
+   buffer containing the blob of data to enqueue
+
+``data_size``
+   size of the ``data`` buffer
+
+Return Values
+-------------
+
+``OPAL_SUCCESS``
+   the variable was appended to the update queue bank successfully
+
+``OPAL_PARAMETER``
+   ``key`` or ``data`` was NULL.
+   ``key`` was empty.
+   ``key_len`` or ``data_size`` was zero.
+   ``key_len``, ``data_size`` is larger than the maximum size
+
+``OPAL_NO_MEM``
+   OPAL was unable to allocate memory for the variable update
+
+``OPAL_HARDWARE``
+   OPAL was unable to write the update to persistant storage
+
+``OPAL_UNSUPPORTED``
+   secure variables are not supported by the platform
+
+``OPAL_RESOURCE``
+   secure variables are supported, but did not initialize properly