Documentation: tee subsystem and op-tee driver

	- directory with info on the /proc/sys/* files.

target/

	- directory with info on generating TCM v4 fabric .ko modules

tee.txt

	- info on the TEE subsystem and drivers

this_cpu_ops.txt

	- List rationale behind and the way to use this_cpu operations.

thermal/

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

  the 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.

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.

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.

F:	include/linux/tee_drv.h

F:	include/uapi/linux/tee.h

F:	drivers/tee/

F:	Documentation/tee.txt

THUNDERBOLT DRIVER

M:	Andreas Noever <andreas.noever@gmail.com>