Reviewed-by: Simon Glass sjg@chromium.org Signed-off-by: Jens Wiklander jens.wiklander@linaro.org --- doc/README.tee | 112 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 doc/README.tee
diff --git a/doc/README.tee b/doc/README.tee new file mode 100644 index 000000000000..79e7996a6f5f --- /dev/null +++ b/doc/README.tee @@ -0,0 +1,112 @@ +============= +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.