Documentation: Destage TEE subsystem documentation

Add a separate documentation directory for TEE subsystem since it is a
standalone subsystem which already offers devices consumed by multiple
different subsystem drivers.

Split overall TEE subsystem documentation modularly where:
- The userspace API has been moved to Documentation/userspace-api/tee.rst.
- The driver API has been moved to Documentation/driver-api/tee.rst.
- The first module covers the overview of TEE subsystem.
- The further modules are dedicated to different TEE implementations like:
  - OP-TEE
  - AMD-TEE
  - and so on for future TEE implementation support.
Acked-by: Rijo Thomas <Rijo-john.Thomas@amd.com>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231128072352.866859-1-sumit.garg@linaro.org

Documentation/driver-api/index.rst

@@ -112,6 +112,7 @@ available subsections can be seen below.
    hte/index
    wmi
    dpll
+   tee
 
 .. only::  subproject and html
 

Documentation/driver-api/tee.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+===============================================
+TEE (Trusted Execution Environment) driver API
+===============================================
+
+Kernel provides a TEE bus infrastructure where a Trusted Application is
+represented as a device identified via Universally Unique Identifier (UUID) and
+client drivers register a table of supported device UUIDs.
+
+TEE bus infrastructure registers following APIs:
+
+match():
+  iterates over the client driver UUID table to find a corresponding
+  match for device UUID. If a match is found, then this particular device is
+  probed via corresponding probe API registered by the client driver. This
+  process happens whenever a device or a client driver is registered with TEE
+  bus.
+
+uevent():
+  notifies user-space (udev) whenever a new device is registered on
+  TEE bus for auto-loading of modularized client drivers.
+
+TEE bus device enumeration is specific to underlying TEE implementation, so it
+is left open for TEE drivers to provide corresponding implementation.
+
+Then TEE client driver can talk to a matched Trusted Application using APIs
+listed in include/linux/tee_drv.h.
+
+TEE client driver example
+-------------------------
+
+Suppose a TEE client driver needs to communicate with a Trusted Application
+having UUID: ``ac6a4085-0e82-4c33-bf98-8eb8e118b6c2``, so driver registration
+snippet would look like::
+
+	static const struct tee_client_device_id client_id_table[] = {
+		{UUID_INIT(0xac6a4085, 0x0e82, 0x4c33,
+			   0xbf, 0x98, 0x8e, 0xb8, 0xe1, 0x18, 0xb6, 0xc2)},
+		{}
+	};
+
+	MODULE_DEVICE_TABLE(tee, client_id_table);
+
+	static struct tee_client_driver client_driver = {
+		.id_table	= client_id_table,
+		.driver		= {
+			.name		= DRIVER_NAME,
+			.bus		= &tee_bus_type,
+			.probe		= client_probe,
+			.remove		= client_remove,
+		},
+	};
+
+	static int __init client_init(void)
+	{
+		return driver_register(&client_driver.driver);
+	}
+
+	static void __exit client_exit(void)
+	{
+		driver_unregister(&client_driver.driver);
+	}
+
+	module_init(client_init);
+	module_exit(client_exit);

Documentation/security/keys/trusted-encrypted.rst

@@ -88,7 +88,7 @@ safe.
      (2) TEE
 
          TEEs have well-documented, standardized client interface and APIs. For
-         more details refer to ``Documentation/staging/tee.rst``.
+         more details refer to ``Documentation/driver-api/tee.rst``.
 
      (3) CAAM
 

Documentation/staging/index.rst

@@ -12,5 +12,4 @@ Unsorted Documentation
    rpmsg
    speculation
    static-keys
-   tee
    xz

Documentation/subsystem-apis.rst

@@ -86,3 +86,4 @@ Storage interfaces
    misc-devices/index
    peci/index
    wmi/index
+   tee/index

Documentation/tee/amd-tee.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+=============================================
+AMD-TEE (AMD's Trusted Execution Environment)
+=============================================
+
+The AMD-TEE driver handles the communication with AMD's TEE environment. The
+TEE environment is provided by AMD Secure Processor.
+
+The AMD Secure Processor (formerly called Platform Security Processor or PSP)
+is a dedicated processor that features ARM TrustZone technology, along with a
+software-based Trusted Execution Environment (TEE) designed to enable
+third-party Trusted Applications. This feature is currently enabled only for
+APUs.
+
+The following picture shows a high level overview of AMD-TEE::
+
+                                             |
+    x86                                      |
+                                             |
+ User space            (Kernel space)        |    AMD Secure Processor (PSP)
+ ~~~~~~~~~~            ~~~~~~~~~~~~~~        |    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+                                             |
+ +--------+                                  |       +-------------+
+ | Client |                                  |       | Trusted     |
+ +--------+                                  |       | Application |
+     /\                                      |       +-------------+
+     ||                                      |             /\
+     ||                                      |             ||
+     ||                                      |             \/
+     ||                                      |         +----------+
+     ||                                      |         |   TEE    |
+     ||                                      |         | Internal |
+     \/                                      |         |   API    |
+ +---------+           +-----------+---------+         +----------+
+ | TEE     |           | TEE       | AMD-TEE |         | AMD-TEE  |
+ | Client  |           | subsystem | driver  |         | Trusted  |
+ | API     |           |           |         |         |   OS     |
+ +---------+-----------+----+------+---------+---------+----------+
+ |   Generic TEE API        |      | ASP     |      Mailbox       |
+ |   IOCTL (TEE_IOC_*)      |      | driver  | Register Protocol  |
+ +--------------------------+      +---------+--------------------+
+
+At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the
+CPU to PSP mailbox register to submit commands to the PSP. The format of the
+command buffer is opaque to the ASP driver. It's role is to submit commands to
+the secure processor and return results to AMD-TEE driver. The interface
+between AMD-TEE driver and AMD Secure Processor driver can be found in [1].
+
+The AMD-TEE driver packages the command buffer payload for processing in TEE.
+The command buffer format for the different TEE commands can be found in [2].
+
+The TEE commands supported by AMD-TEE Trusted OS are:
+
+* TEE_CMD_ID_LOAD_TA          - loads a Trusted Application (TA) binary into
+                                TEE environment.
+* TEE_CMD_ID_UNLOAD_TA        - unloads TA binary from TEE environment.
+* TEE_CMD_ID_OPEN_SESSION     - opens a session with a loaded TA.
+* TEE_CMD_ID_CLOSE_SESSION    - closes session with loaded TA
+* TEE_CMD_ID_INVOKE_CMD       - invokes a command with loaded TA
+* TEE_CMD_ID_MAP_SHARED_MEM   - maps shared memory
+* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory
+
+AMD-TEE Trusted OS is the firmware running on AMD Secure Processor.
+
+The AMD-TEE driver registers itself with TEE subsystem and implements the
+following driver function callbacks:
+
+* get_version - returns the driver implementation id and capability.
+* open - sets up the driver context data structure.
+* release - frees up driver resources.
+* open_session - loads the TA binary and opens session with loaded TA.
+* close_session -  closes session with loaded TA and unloads it.
+* invoke_func - invokes a command with loaded TA.
+
+cancel_req driver callback is not supported by AMD-TEE.
+
+The GlobalPlatform TEE Client API [3] can be used by the user space (client) to
+talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening
+a session, invoking commands and closing session with TA.
+
+References
+==========
+
+[1] include/linux/psp-tee.h
+
+[2] drivers/tee/amdtee/amdtee_if.h
+
+[3] http://www.globalplatform.org/specificationsdevice.asp look for
+    "TEE Client API Specification v1.0" and click download.

Documentation/tee/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+TEE Subsystem
+=============
+
+.. toctree::
+   :maxdepth: 1
+
+   tee
+   op-tee
+   amd-tee
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/staging/tee.rst → Documentation/tee/op-tee.rst

-=============
-TEE subsystem
-=============
+.. SPDX-License-Identifier: GPL-2.0
 
-This document describes the TEE subsystem in Linux.
-
-A TEE (Trusted Execution Environment) is a trusted OS running in some
-secure environment, for example, TrustZone on ARM CPUs, or a separate
-secure co-processor etc. A TEE driver handles the details needed to
-communicate with the TEE.
-
-This subsystem deals with:
-
-- Registration of TEE drivers
-
-- Managing shared memory between Linux and the TEE
-
-- Providing a generic API to the TEE
-
-The TEE interface
-=================
-
-include/uapi/linux/tee.h defines the generic interface to a TEE.
-
-User space (the client) connects to the driver by opening /dev/tee[0-9]* or
-/dev/teepriv[0-9]*.
-
-- TEE_IOC_SHM_ALLOC allocates shared memory and returns a file descriptor
-  which user space can mmap. When user space doesn't need the file
-  descriptor any more, it should be closed. When shared memory isn't needed
-  any longer it should be unmapped with munmap() to allow the reuse of
-  memory.
-
-- TEE_IOC_VERSION lets user space know which TEE this driver handles and
-  its capabilities.
-
-- TEE_IOC_OPEN_SESSION opens a new session to a Trusted Application.
-
-- TEE_IOC_INVOKE invokes a function in a Trusted Application.
-
-- TEE_IOC_CANCEL may cancel an ongoing TEE_IOC_OPEN_SESSION or TEE_IOC_INVOKE.
-
-- TEE_IOC_CLOSE_SESSION closes a session to a Trusted Application.
-
-There are two classes of clients, normal clients and supplicants. The latter is
-a helper process for the TEE to access resources in Linux, for example file
-system access. A normal client opens /dev/tee[0-9]* and a supplicant opens
-/dev/teepriv[0-9].
-
-Much of the communication between clients and the TEE is opaque to the
-driver. The main job for the driver is to receive requests from the
-clients, forward them to the TEE and send back the results. In the case of
-supplicants the communication goes in the other direction, the TEE sends
-requests to the supplicant which then sends back the result.
-
-The TEE kernel interface
-========================
-
-Kernel provides a TEE bus infrastructure where a Trusted Application is
-represented as a device identified via Universally Unique Identifier (UUID) and
-client drivers register a table of supported device UUIDs.
-
-TEE bus infrastructure registers following APIs:
-
-match():
-  iterates over the client driver UUID table to find a corresponding
-  match for device UUID. If a match is found, then this particular device is
-  probed via corresponding probe API registered by the client driver. This
-  process happens whenever a device or a client driver is registered with TEE
-  bus.
-
-uevent():
-  notifies user-space (udev) whenever a new device is registered on
-  TEE bus for auto-loading of modularized client drivers.
-
-TEE bus device enumeration is specific to underlying TEE implementation, so it
-is left open for TEE drivers to provide corresponding implementation.
-
-Then TEE client driver can talk to a matched Trusted Application using APIs
-listed in include/linux/tee_drv.h.
-
-TEE client driver example
--------------------------
-
-Suppose a TEE client driver needs to communicate with a Trusted Application
-having UUID: ``ac6a4085-0e82-4c33-bf98-8eb8e118b6c2``, so driver registration
-snippet would look like::
-
-	static const struct tee_client_device_id client_id_table[] = {
-		{UUID_INIT(0xac6a4085, 0x0e82, 0x4c33,
-			   0xbf, 0x98, 0x8e, 0xb8, 0xe1, 0x18, 0xb6, 0xc2)},
-		{}
-	};
-
-	MODULE_DEVICE_TABLE(tee, client_id_table);
-
-	static struct tee_client_driver client_driver = {
-		.id_table	= client_id_table,
-		.driver		= {
-			.name		= DRIVER_NAME,
-			.bus		= &tee_bus_type,
-			.probe		= client_probe,
-			.remove		= client_remove,
-		},
-	};
-
-	static int __init client_init(void)
-	{
-		return driver_register(&client_driver.driver);
-	}
-
-	static void __exit client_exit(void)
-	{
-		driver_unregister(&client_driver.driver);
-	}
-
-	module_init(client_init);
-	module_exit(client_exit);
-
-OP-TEE driver
-=============
+====================================================
+OP-TEE (Open Portable Trusted Execution Environment)
+====================================================
 
 The OP-TEE driver handles OP-TEE [1] based TEEs. Currently it is only the ARM
 TrustZone based OP-TEE solution that is supported.
@@ -221,7 +105,7 @@ The OPTEE_INSECURE_LOAD_IMAGE Kconfig option enables the ability to load the
 BL32 OP-TEE image from the kernel after the kernel boots, rather than loading
 it from the firmware before the kernel boots. This also requires enabling the
 corresponding option in Trusted Firmware for Arm. The Trusted Firmware for Arm
-documentation [8] explains the security threat associated with enabling this as
+documentation [6] explains the security threat associated with enabling this as
 well as mitigations at the firmware and platform level.
 
 There are additional attack vectors/mitigations for the kernel that should be
@@ -265,84 +149,6 @@ addressed when using this option.
      rather than as a module to prevent exploits that may cause the module to
      not be loaded.
 
-AMD-TEE driver
-==============
-
-The AMD-TEE driver handles the communication with AMD's TEE environment. The
-TEE environment is provided by AMD Secure Processor.
-
-The AMD Secure Processor (formerly called Platform Security Processor or PSP)
-is a dedicated processor that features ARM TrustZone technology, along with a
-software-based Trusted Execution Environment (TEE) designed to enable
-third-party Trusted Applications. This feature is currently enabled only for
-APUs.
-
-The following picture shows a high level overview of AMD-TEE::
-
-                                             |
-    x86                                      |
-                                             |
- User space            (Kernel space)        |    AMD Secure Processor (PSP)
- ~~~~~~~~~~            ~~~~~~~~~~~~~~        |    ~~~~~~~~~~~~~~~~~~~~~~~~~~
-                                             |
- +--------+                                  |       +-------------+
- | Client |                                  |       | Trusted     |
- +--------+                                  |       | Application |
-     /\                                      |       +-------------+
-     ||                                      |             /\
-     ||                                      |             ||
-     ||                                      |             \/
-     ||                                      |         +----------+
-     ||                                      |         |   TEE    |
-     ||                                      |         | Internal |
-     \/                                      |         |   API    |
- +---------+           +-----------+---------+         +----------+
- | TEE     |           | TEE       | AMD-TEE |         | AMD-TEE  |
- | Client  |           | subsystem | driver  |         | Trusted  |
- | API     |           |           |         |         |   OS     |
- +---------+-----------+----+------+---------+---------+----------+
- |   Generic TEE API        |      | ASP     |      Mailbox       |
- |   IOCTL (TEE_IOC_*)      |      | driver  | Register Protocol  |
- +--------------------------+      +---------+--------------------+
-
-At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the
-CPU to PSP mailbox register to submit commands to the PSP. The format of the
-command buffer is opaque to the ASP driver. It's role is to submit commands to
-the secure processor and return results to AMD-TEE driver. The interface
-between AMD-TEE driver and AMD Secure Processor driver can be found in [6].
-
-The AMD-TEE driver packages the command buffer payload for processing in TEE.
-The command buffer format for the different TEE commands can be found in [7].
-
-The TEE commands supported by AMD-TEE Trusted OS are:
-
-* TEE_CMD_ID_LOAD_TA          - loads a Trusted Application (TA) binary into
-                                TEE environment.
-* TEE_CMD_ID_UNLOAD_TA        - unloads TA binary from TEE environment.
-* TEE_CMD_ID_OPEN_SESSION     - opens a session with a loaded TA.
-* TEE_CMD_ID_CLOSE_SESSION    - closes session with loaded TA
-* TEE_CMD_ID_INVOKE_CMD       - invokes a command with loaded TA
-* TEE_CMD_ID_MAP_SHARED_MEM   - maps shared memory
-* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory
-
-AMD-TEE Trusted OS is the firmware running on AMD Secure Processor.
-
-The AMD-TEE driver registers itself with TEE subsystem and implements the
-following driver function callbacks:
-
-* get_version - returns the driver implementation id and capability.
-* open - sets up the driver context data structure.
-* release - frees up driver resources.
-* open_session - loads the TA binary and opens session with loaded TA.
-* close_session -  closes session with loaded TA and unloads it.
-* invoke_func - invokes a command with loaded TA.
-
-cancel_req driver callback is not supported by AMD-TEE.
-
-The GlobalPlatform TEE Client API [5] can be used by the user space (client) to
-talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening
-a session, invoking commands and closing session with TA.
-
 References
 ==========
 
@@ -357,8 +163,4 @@ References
 [5] http://www.globalplatform.org/specificationsdevice.asp look for
     "TEE Client API Specification v1.0" and click download.
 
-[6] include/linux/psp-tee.h
-
-[7] drivers/tee/amdtee/amdtee_if.h
-
-[8] https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model.html
+[6] https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model.html

Documentation/tee/tee.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+TEE (Trusted Execution Environment)
+===================================
+
+This document describes the TEE subsystem in Linux.
+
+Overview
+========
+
+A TEE is a trusted OS running in some secure environment, for example,
+TrustZone on ARM CPUs, or a separate secure co-processor etc. A TEE driver
+handles the details needed to communicate with the TEE.
+
+This subsystem deals with:
+
+- Registration of TEE drivers
+
+- Managing shared memory between Linux and the TEE
+
+- Providing a generic API to the TEE

Documentation/userspace-api/index.rst

@@ -30,6 +30,7 @@ place where this information is gathered.
    sysfs-platform_profile
    vduse
    futex2
+   tee
 
 .. only::  subproject and html
 

Documentation/userspace-api/tee.rst

+.. SPDX-License-Identifier: GPL-2.0
+.. tee:
+
+==================================================
+TEE (Trusted Execution Environment) Userspace API
+==================================================
+
+include/uapi/linux/tee.h defines the generic interface to a TEE.
+
+User space (the client) connects to the driver by opening /dev/tee[0-9]* or
+/dev/teepriv[0-9]*.
+
+- TEE_IOC_SHM_ALLOC allocates shared memory and returns a file descriptor
+  which user space can mmap. When user space doesn't need the file
+  descriptor any more, it should be closed. When shared memory isn't needed
+  any longer it should be unmapped with munmap() to allow the reuse of
+  memory.
+
+- TEE_IOC_VERSION lets user space know which TEE this driver handles and
+  its capabilities.
+
+- TEE_IOC_OPEN_SESSION opens a new session to a Trusted Application.
+
+- TEE_IOC_INVOKE invokes a function in a Trusted Application.
+
+- TEE_IOC_CANCEL may cancel an ongoing TEE_IOC_OPEN_SESSION or TEE_IOC_INVOKE.
+
+- TEE_IOC_CLOSE_SESSION closes a session to a Trusted Application.
+
+There are two classes of clients, normal clients and supplicants. The latter is
+a helper process for the TEE to access resources in Linux, for example file
+system access. A normal client opens /dev/tee[0-9]* and a supplicant opens
+/dev/teepriv[0-9].
+
+Much of the communication between clients and the TEE is opaque to the
+driver. The main job for the driver is to receive requests from the
+clients, forward them to the TEE and send back the results. In the case of
+supplicants the communication goes in the other direction, the TEE sends
+requests to the supplicant which then sends back the result.

MAINTAINERS

@@ -21351,7 +21351,9 @@ M:	Jens Wiklander <jens.wiklander@linaro.org>
 R:	Sumit Garg <sumit.garg@linaro.org>
 L:	op-tee@lists.trustedfirmware.org
 S:	Maintained
-F:	Documentation/staging/tee.rst
+F:	Documentation/driver-api/tee.rst
+F:	Documentation/tee/
+F:	Documentation/userspace-api/tee.rst
 F:	drivers/tee/
 F:	include/linux/tee_drv.h
 F:	include/uapi/linux/tee.h

drivers/tee/optee/Kconfig

@@ -23,4 +23,4 @@ config OPTEE_INSECURE_LOAD_IMAGE
 	  https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model.html
 
 	  Additional documentation on kernel security risks are at
-	  Documentation/staging/tee.rst.
+	  Documentation/tee/op-tee.rst.