Documentation/staging/tee.rst - linux - Git at Google

 =============
 TEE subsystem
 =============

 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
 =============

 The OP-TEE driver handles OP-TEE [1] based TEEs. Currently it is only the ARM
 TrustZone based OP-TEE solution that is supported.

 Lowest level of communication with OP-TEE builds on ARM SMC Calling
 Convention (SMCCC) [2], which is the foundation for OP-TEE's SMC interface
 [3] used internally by the driver. Stacked on top of that is OP-TEE Message
 Protocol [4].

 OP-TEE SMC interface provides the basic functions required by SMCCC and some
 additional functions specific for OP-TEE. The most interesting functions are:

 - OPTEE_SMC_FUNCID_CALLS_UID (part of SMCCC) returns the version information
   which is then returned by TEE_IOC_VERSION

 - OPTEE_SMC_CALL_GET_OS_UUID returns the particular OP-TEE implementation, used
   to tell, for instance, a TrustZone OP-TEE apart from an OP-TEE running on a
   separate secure co-processor.

 - OPTEE_SMC_CALL_WITH_ARG drives the OP-TEE message protocol

 - OPTEE_SMC_GET_SHM_CONFIG lets the driver and OP-TEE agree on which memory
   range to used for shared memory between Linux and OP-TEE.

 The GlobalPlatform TEE Client API [5] is implemented on top of the generic
 TEE API.

 Picture of the relationship between the different components in the
 OP-TEE architecture::

       User space                  Kernel                   Secure world
       ~~~~~~~~~~                  ~~~~~~                   ~~~~~~~~~~~~
    +--------+                                             +-------------+
    | Client |                                             | Trusted     |
    +--------+                                             | Application |
       /\                                                  +-------------+
       || +----------+                                           /\
       || |tee-      |                                           ||
       || |supplicant|                                           \/
       || +----------+                                     +-------------+
       \/      /\                                          | TEE Internal|
    +-------+  ||                                          | API         |
    + TEE   |  ||            +--------+--------+           +-------------+
    | Client|  ||            | TEE    | OP-TEE |           | OP-TEE      |
    | API   |  \/            | subsys | driver |           | Trusted OS  |
    +-------+----------------+----+-------+----+-----------+-------------+
    |      Generic TEE API        |       |     OP-TEE MSG               |
    |      IOCTL (TEE_IOC_*)      |       |     SMCCC (OPTEE_SMC_CALL_*) |
    +-----------------------------+       +------------------------------+

 RPC (Remote Procedure Call) are requests from secure world to kernel driver
 or tee-supplicant. An RPC is identified by a special range of SMCCC return
 values from OPTEE_SMC_CALL_WITH_ARG. RPC messages which are intended for the
 kernel are handled by the kernel driver. Other RPC messages will be forwarded to
 tee-supplicant without further involvement of the driver, except switching
 shared memory buffer representation.

 OP-TEE device enumeration
 -------------------------

 OP-TEE provides a pseudo Trusted Application: drivers/tee/optee/device.c in
 order to support device enumeration. In other words, OP-TEE driver invokes this
 application to retrieve a list of Trusted Applications which can be registered
 as devices on the TEE bus.

 OP-TEE notifications
 --------------------

 There are two kinds of notifications that secure world can use to make
 normal world aware of some event.

 1. Synchronous notifications delivered with ``OPTEE_RPC_CMD_NOTIFICATION``
    using the ``OPTEE_RPC_NOTIFICATION_SEND`` parameter.
 2. Asynchronous notifications delivered with a combination of a non-secure
    edge-triggered interrupt and a fast call from the non-secure interrupt
    handler.

 Synchronous notifications are limited by depending on RPC for delivery,
 this is only usable when secure world is entered with a yielding call via
 ``OPTEE_SMC_CALL_WITH_ARG``. This excludes such notifications from secure
 world interrupt handlers.

 An asynchronous notification is delivered via a non-secure edge-triggered
 interrupt to an interrupt handler registered in the OP-TEE driver. The
 actual notification value are retrieved with the fast call
 ``OPTEE_SMC_GET_ASYNC_NOTIF_VALUE``. Note that one interrupt can represent
 multiple notifications.

 One notification value ``OPTEE_SMC_ASYNC_NOTIF_VALUE_DO_BOTTOM_HALF`` has a
 special meaning. When this value is received it means that normal world is
 supposed to make a yielding call ``OPTEE_MSG_CMD_DO_BOTTOM_HALF``. This
 call is done from the thread assisting the interrupt handler. This is a
 building block for OP-TEE OS in secure world to implement the top half and
 bottom half style of device drivers.

 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
 ==========

 [1] https://github.com/OP-TEE/optee_os

 [2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html

 [3] drivers/tee/optee/optee_smc.h

 [4] drivers/tee/optee/optee_msg.h

 [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
	=============
	TEE subsystem
	=============

	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
	=============

	The OP-TEE driver handles OP-TEE [1] based TEEs. Currently it is only the ARM
	TrustZone based OP-TEE solution that is supported.

	Lowest level of communication with OP-TEE builds on ARM SMC Calling
	Convention (SMCCC) [2], which is the foundation for OP-TEE's SMC interface
	[3] used internally by the driver. Stacked on top of that is OP-TEE Message
	Protocol [4].

	OP-TEE SMC interface provides the basic functions required by SMCCC and some
	additional functions specific for OP-TEE. The most interesting functions are:

	- OPTEE_SMC_FUNCID_CALLS_UID (part of SMCCC) returns the version information
	which is then returned by TEE_IOC_VERSION

	- OPTEE_SMC_CALL_GET_OS_UUID returns the particular OP-TEE implementation, used
	to tell, for instance, a TrustZone OP-TEE apart from an OP-TEE running on a
	separate secure co-processor.

	- OPTEE_SMC_CALL_WITH_ARG drives the OP-TEE message protocol

	- OPTEE_SMC_GET_SHM_CONFIG lets the driver and OP-TEE agree on which memory
	range to used for shared memory between Linux and OP-TEE.

	The GlobalPlatform TEE Client API [5] is implemented on top of the generic
	TEE API.

	Picture of the relationship between the different components in the
	OP-TEE architecture::

	User space Kernel Secure world
	~~~~~~~~~~ ~~~~~~ ~~~~~~~~~~~~
	+--------+ +-------------+
	\| Client \| \| Trusted \|
	+--------+ \| Application \|
	/\ +-------------+
	\|\| +----------+ /\
	\|\| \|tee- \| \|\|
	\|\| \|supplicant\| \/
	\|\| +----------+ +-------------+
	\/ /\ \| TEE Internal\|
	+-------+ \|\| \| API \|
	+ TEE \| \|\| +--------+--------+ +-------------+
	\| Client\| \|\| \| TEE \| OP-TEE \| \| OP-TEE \|
	\| API \| \/ \| subsys \| driver \| \| Trusted OS \|
	+-------+----------------+----+-------+----+-----------+-------------+
	\| Generic TEE API \| \| OP-TEE MSG \|
	\| IOCTL (TEE_IOC_) \| \| SMCCC (OPTEE_SMC_CALL_) \|
	+-----------------------------+ +------------------------------+

	RPC (Remote Procedure Call) are requests from secure world to kernel driver
	or tee-supplicant. An RPC is identified by a special range of SMCCC return
	values from OPTEE_SMC_CALL_WITH_ARG. RPC messages which are intended for the
	kernel are handled by the kernel driver. Other RPC messages will be forwarded to
	tee-supplicant without further involvement of the driver, except switching
	shared memory buffer representation.

	OP-TEE device enumeration
	-------------------------

	OP-TEE provides a pseudo Trusted Application: drivers/tee/optee/device.c in
	order to support device enumeration. In other words, OP-TEE driver invokes this
	application to retrieve a list of Trusted Applications which can be registered
	as devices on the TEE bus.

	OP-TEE notifications
	--------------------

	There are two kinds of notifications that secure world can use to make
	normal world aware of some event.

	1. Synchronous notifications delivered with ``OPTEE_RPC_CMD_NOTIFICATION``
	using the ``OPTEE_RPC_NOTIFICATION_SEND`` parameter.
	2. Asynchronous notifications delivered with a combination of a non-secure
	edge-triggered interrupt and a fast call from the non-secure interrupt
	handler.

	Synchronous notifications are limited by depending on RPC for delivery,
	this is only usable when secure world is entered with a yielding call via
	``OPTEE_SMC_CALL_WITH_ARG``. This excludes such notifications from secure
	world interrupt handlers.

	An asynchronous notification is delivered via a non-secure edge-triggered
	interrupt to an interrupt handler registered in the OP-TEE driver. The
	actual notification value are retrieved with the fast call
	``OPTEE_SMC_GET_ASYNC_NOTIF_VALUE``. Note that one interrupt can represent
	multiple notifications.

	One notification value ``OPTEE_SMC_ASYNC_NOTIF_VALUE_DO_BOTTOM_HALF`` has a
	special meaning. When this value is received it means that normal world is
	supposed to make a yielding call ``OPTEE_MSG_CMD_DO_BOTTOM_HALF``. This
	call is done from the thread assisting the interrupt handler. This is a
	building block for OP-TEE OS in secure world to implement the top half and
	bottom half style of device drivers.

	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
	==========

	[1] https://github.com/OP-TEE/optee_os

	[2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html

	[3] drivers/tee/optee/optee_smc.h

	[4] drivers/tee/optee/optee_msg.h

	[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