LXR linux/Documentation/tee.txt

   1=============
   2TEE subsystem
   3=============
   4
   5This document describes the TEE subsystem in Linux.
   6
   7A TEE (Trusted Execution Environment) is a trusted OS running in some
   8secure environment, for example, TrustZone on ARM CPUs, or a separate
   9secure co-processor etc. A TEE driver handles the details needed to
  10communicate with the TEE.
  11
  12This 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
  20The TEE interface
  21=================
  22
  23include/uapi/linux/tee.h defines the generic interface to a TEE.
  24
  25User 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
  45There are two classes of clients, normal clients and supplicants. The latter is
  46a helper process for the TEE to access resources in Linux, for example file
  47system access. A normal client opens /dev/tee[0-9]* and a supplicant opens
  48/dev/teepriv[0-9].
  49
  50Much of the communication between clients and the TEE is opaque to the
  51driver. The main job for the driver is to receive requests from the
  52clients, forward them to the TEE and send back the results. In the case of
  53supplicants the communication goes in the other direction, the TEE sends
  54requests to the supplicant which then sends back the result.
  55
  56OP-TEE driver
  57=============
  58
  59The OP-TEE driver handles OP-TEE [1] based TEEs. Currently it is only the ARM
  60TrustZone based OP-TEE solution that is supported.
  61
  62Lowest level of communication with OP-TEE builds on ARM SMC Calling
  63Convention (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
  65Protocol [4].
  66
  67OP-TEE SMC interface provides the basic functions required by SMCCC and some
  68additional 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
  82The GlobalPlatform TEE Client API [5] is implemented on top of the generic
  83TEE API.
  84
  85Picture of the relationship between the different components in the
  86OP-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
 108RPC (Remote Procedure Call) are requests from secure world to kernel driver
 109or tee-supplicant. An RPC is identified by a special range of SMCCC return
 110values from OPTEE_SMC_CALL_WITH_ARG. RPC messages which are intended for the
 111kernel are handled by the kernel driver. Other RPC messages will be forwarded to
 112tee-supplicant without further involvement of the driver, except switching
 113shared memory buffer representation.
 114
 115References
 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.
 128