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- =============
- TEE uclass
- =============
- This document describes the TEE uclass in U-Boot
- 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 uclass deals with:
- - Registration of TEE drivers
- - Managing shared memory between U-Boot and the TEE
- - Providing a generic API to the TEE
- The TEE interface
- =================
- include/tee.h defines the generic interface to a TEE.
- A client finds the TEE device via tee_find_device(). Other important functions
- when interfacing with a TEE are:
- - tee_shm_alloc(), tee_shm_register() and tee_shm_free() to manage shared
- memory objects often needed when communicating with the TEE.
- - tee_get_version() lets the client know which the capabilities of the TEE
- device.
- - tee_open_session() opens a session to a Trusted Application
- - tee_invoke_func() invokes a function in a Trusted Application
- - tee_close_session() closes a session to a Trusted Application
- 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.
- 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:
- U-Boot Secure world
- ~~~~~~ ~~~~~~~~~~~~
- +------------+ +-------------+
- | Client | | Trusted |
- | | | Application |
- +------------+ +-------------+
- /\ /\
- || ||
- \/ \/
- +------------+ +-------------+
- | TEE | | TEE Internal|
- | uclass | | API |
- +------------+ +-------------+
- | OP-TEE | | OP-TEE |
- | driver | | Trusted OS |
- +------------+-----------+-------------+
- | OP-TEE MSG |
- | SMCCC (OPTEE_SMC_CALL_*) |
- +--------------------------------------+
- RPC (Remote Procedure Call) are requests from secure world to the driver.
- An RPC is identified by a special range of SMCCC return values from
- OPTEE_SMC_CALL_WITH_ARG.
- 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.
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