About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / tee.txt




Custom Search

Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

1	=============
2	TEE subsystem
3	=============
4	
5	This document describes the TEE subsystem in Linux.
6	
7	A TEE (Trusted Execution Environment) is a trusted OS running in some
8	secure environment, for example, TrustZone on ARM CPUs, or a separate
9	secure co-processor etc. A TEE driver handles the details needed to
10	communicate with the TEE.
11	
12	This subsystem deals with:
13	
14	- Registration of TEE drivers
15	
16	- Managing shared memory between Linux and the TEE
17	
18	- Providing a generic API to the TEE
19	
20	The TEE interface
21	=================
22	
23	include/uapi/linux/tee.h defines the generic interface to a TEE.
24	
25	User space (the client) connects to the driver by opening /dev/tee[0-9]* or
26	/dev/teepriv[0-9]*.
27	
28	- TEE_IOC_SHM_ALLOC allocates shared memory and returns a file descriptor
29	  which user space can mmap. When user space doesn't need the file
30	  descriptor any more, it should be closed. When shared memory isn't needed
31	  any longer it should be unmapped with munmap() to allow the reuse of
32	  memory.
33	
34	- TEE_IOC_VERSION lets user space know which TEE this driver handles and
35	  the its capabilities.
36	
37	- TEE_IOC_OPEN_SESSION opens a new session to a Trusted Application.
38	
39	- TEE_IOC_INVOKE invokes a function in a Trusted Application.
40	
41	- TEE_IOC_CANCEL may cancel an ongoing TEE_IOC_OPEN_SESSION or TEE_IOC_INVOKE.
42	
43	- TEE_IOC_CLOSE_SESSION closes a session to a Trusted Application.
44	
45	There are two classes of clients, normal clients and supplicants. The latter is
46	a helper process for the TEE to access resources in Linux, for example file
47	system access. A normal client opens /dev/tee[0-9]* and a supplicant opens
48	/dev/teepriv[0-9].
49	
50	Much of the communication between clients and the TEE is opaque to the
51	driver. The main job for the driver is to receive requests from the
52	clients, forward them to the TEE and send back the results. In the case of
53	supplicants the communication goes in the other direction, the TEE sends
54	requests to the supplicant which then sends back the result.
55	
56	OP-TEE driver
57	=============
58	
59	The OP-TEE driver handles OP-TEE [1] based TEEs. Currently it is only the ARM
60	TrustZone based OP-TEE solution that is supported.
61	
62	Lowest level of communication with OP-TEE builds on ARM SMC Calling
63	Convention (SMCCC) [2], which is the foundation for OP-TEE's SMC interface
64	[3] used internally by the driver. Stacked on top of that is OP-TEE Message
65	Protocol [4].
66	
67	OP-TEE SMC interface provides the basic functions required by SMCCC and some
68	additional functions specific for OP-TEE. The most interesting functions are:
69	
70	- OPTEE_SMC_FUNCID_CALLS_UID (part of SMCCC) returns the version information
71	  which is then returned by TEE_IOC_VERSION
72	
73	- OPTEE_SMC_CALL_GET_OS_UUID returns the particular OP-TEE implementation, used
74	  to tell, for instance, a TrustZone OP-TEE apart from an OP-TEE running on a
75	  separate secure co-processor.
76	
77	- OPTEE_SMC_CALL_WITH_ARG drives the OP-TEE message protocol
78	
79	- OPTEE_SMC_GET_SHM_CONFIG lets the driver and OP-TEE agree on which memory
80	  range to used for shared memory between Linux and OP-TEE.
81	
82	The GlobalPlatform TEE Client API [5] is implemented on top of the generic
83	TEE API.
84	
85	Picture of the relationship between the different components in the
86	OP-TEE architecture::
87	
88	      User space                  Kernel                   Secure world
89	      ~~~~~~~~~~                  ~~~~~~                   ~~~~~~~~~~~~
90	   +--------+                                             +-------------+
91	   | Client |                                             | Trusted     |
92	   +--------+                                             | Application |
93	      /\                                                  +-------------+
94	      || +----------+                                           /\
95	      || |tee-      |                                           ||
96	      || |supplicant|                                           \/
97	      || +----------+                                     +-------------+
98	      \/      /\                                          | TEE Internal|
99	   +-------+  ||                                          | API         |
100	   + TEE   |  ||            +--------+--------+           +-------------+
101	   | Client|  ||            | TEE    | OP-TEE |           | OP-TEE      |
102	   | API   |  \/            | subsys | driver |           | Trusted OS  |
103	   +-------+----------------+----+-------+----+-----------+-------------+
104	   |      Generic TEE API        |       |     OP-TEE MSG               |
105	   |      IOCTL (TEE_IOC_*)      |       |     SMCCC (OPTEE_SMC_CALL_*) |
106	   +-----------------------------+       +------------------------------+
107	
108	RPC (Remote Procedure Call) are requests from secure world to kernel driver
109	or tee-supplicant. An RPC is identified by a special range of SMCCC return
110	values from OPTEE_SMC_CALL_WITH_ARG. RPC messages which are intended for the
111	kernel are handled by the kernel driver. Other RPC messages will be forwarded to
112	tee-supplicant without further involvement of the driver, except switching
113	shared memory buffer representation.
114	
115	References
116	==========
117	
118	[1] https://github.com/OP-TEE/optee_os
119	
120	[2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
121	
122	[3] drivers/tee/optee/optee_smc.h
123	
124	[4] drivers/tee/optee/optee_msg.h
125	
126	[5] http://www.globalplatform.org/specificationsdevice.asp look for
127	    "TEE Client API Specification v1.0" and click download.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.