Update tee.txt with AMD-TEE driver details. The driver is written to communicate with AMD's TEE. Acked-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx> Co-developed-by: Devaraj Rangasamy <Devaraj.Rangasamy@xxxxxxx> Signed-off-by: Devaraj Rangasamy <Devaraj.Rangasamy@xxxxxxx> Signed-off-by: Rijo Thomas <Rijo-john.Thomas@xxxxxxx> --- Documentation/tee.txt | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) diff --git a/Documentation/tee.txt b/Documentation/tee.txt index afacdf2..c8fad81 100644 --- a/Documentation/tee.txt +++ b/Documentation/tee.txt @@ -112,6 +112,83 @@ 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. +AMD-TEE driver +============== + +The AMD-TEE driver handles the communication with AMD's TEE environment. The +TEE environment is provided by AMD Secure Processor. + +The AMD Secure Processor (formerly called Platform Security Processor or PSP) +is a dedicated processor that features ARM TrustZone technology, along with a +software-based Trusted Execution Environment (TEE) designed to enable +third-party Trusted Applications. This feature is currently enabled only for +APUs. + +The following picture shows a high level overview of AMD-TEE:: + + | + x86 | + | + User space (Kernel space) | AMD Secure Processor (PSP) + ~~~~~~~~~~ ~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~~~~~~~~~ + | + +--------+ | +-------------+ + | Client | | | Trusted | + +--------+ | | Application | + /\ | +-------------+ + || | /\ + || | || + || | \/ + || | +----------+ + || | | TEE | + || | | Internal | + \/ | | API | + +---------+ +-----------+---------+ +----------+ + | TEE | | TEE | AMD-TEE | | AMD-TEE | + | Client | | subsystem | driver | | Trusted | + | API | | | | | OS | + +---------+-----------+----+------+---------+---------+----------+ + | Generic TEE API | | ASP | Mailbox | + | IOCTL (TEE_IOC_*) | | driver | Register Protocol | + +--------------------------+ +---------+--------------------+ + +At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the +CPU to PSP mailbox regsister to submit commands to the PSP. The format of the +command buffer is opaque to the ASP driver. It's role is to submit commands to +the secure processor and return results to AMD-TEE driver. The interface +between AMD-TEE driver and AMD Secure Processor driver can be found in [6]. + +The AMD-TEE driver packages the command buffer payload for processing in TEE. +The command buffer format for the different TEE commands can be found in [7]. + +The TEE commands supported by AMD-TEE Trusted OS are: +* TEE_CMD_ID_LOAD_TA - loads a Trusted Application (TA) binary into + TEE environment. +* TEE_CMD_ID_UNLOAD_TA - unloads TA binary from TEE environment. +* TEE_CMD_ID_OPEN_SESSION - opens a session with a loaded TA. +* TEE_CMD_ID_CLOSE_SESSION - closes session with loaded TA +* TEE_CMD_ID_INVOKE_CMD - invokes a command with loaded TA +* TEE_CMD_ID_MAP_SHARED_MEM - maps shared memory +* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory + +AMD-TEE Trusted OS is the firmware running on AMD Secure Processor. + +The AMD-TEE driver registers itself with TEE subsystem and implements the +following driver function callbacks: + +* get_version - returns the driver implementation id and capability. +* open - sets up the driver context data structure. +* release - frees up driver resources. +* open_session - loads the TA binary and opens session with loaded TA. +* close_session - closes session with loaded TA and unloads it. +* invoke_func - invokes a command with loaded TA. + +cancel_req driver callback is not supported by AMD-TEE. + +The GlobalPlatform TEE Client API [5] can be used by the user space (client) to +talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening +a session, invoking commands and clossing session with TA. + References ========== @@ -125,3 +202,7 @@ References [5] http://www.globalplatform.org/specificationsdevice.asp look for "TEE Client API Specification v1.0" and click download. + +[6] include/linux/psp-tee.h + +[7] drivers/tee/amdtee/amdtee_if.h -- 1.9.1
