Add documentation for the Qualcomm TEE driver.
Signed-off-by: Amirreza Zarrabi amirreza.zarrabi@oss.qualcomm.com --- Documentation/tee/index.rst | 1 + Documentation/tee/qtee.rst | 150 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 151 insertions(+)
diff --git a/Documentation/tee/index.rst b/Documentation/tee/index.rst index 4be6e69d7837..62afb7ee9b52 100644 --- a/Documentation/tee/index.rst +++ b/Documentation/tee/index.rst @@ -11,6 +11,7 @@ TEE Subsystem op-tee amd-tee ts-tee + qtee
.. only:: subproject and html
diff --git a/Documentation/tee/qtee.rst b/Documentation/tee/qtee.rst new file mode 100644 index 000000000000..8ae4da17c3a7 --- /dev/null +++ b/Documentation/tee/qtee.rst @@ -0,0 +1,150 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================= +QTEE (Qualcomm Trusted Execution Environment) +============================================= + +The QTEE driver handles communication with Qualcomm TEE [1]. + +The lowest level of communication with QTEE builds on the ARM SMC Calling +Convention (SMCCC) [2], which is the foundation for QTEE's Secure Channel +Manager (SCM) [3] used internally by the driver [4]. + +In a QTEE-based system, services are represented as objects with a series of +operations that can be called to produce results, including other objects. + +When an object is hosted within QTEE, executing its operations is referred +to as direct invocation. QTEE can invoke objects hosted in the kernel or +userspace using a method known as callback requests. + +The SCM provides two functions for direct invocation and callback request: + +- QCOM_SCM_SMCINVOKE_INVOKE for direct invocation. It can return either + a result or a callback request. +- QCOM_SCM_SMCINVOKE_CB_RSP submits a response for a previous callback request. + +The QTEE Transport Message [5] is stacked on top of the SCM driver functions. + +A message consists of two buffers shared with QTEE: inbound and outbound +buffers. The inbound buffer is used for direct invocation, and the outbound +buffer is used to make callback requests. This picture shows the contents of +a QTEE transport message:: + + +---------------------+ + | v + +-----------------+-------+-------+------+--------------------------+ + | qcomtee_msg_ |object | buffer | | + | object_invoke | id | offset, size | | (inbound buffer) + +-----------------+-------+--------------+--------------------------+ + <---- header -----><---- arguments ------><- in/out buffer payload -> + + +-----------+ + | v + +-----------------+-------+-------+------+----------------------+ + | qcomtee_msg_ |object | buffer | | + | callback | id | offset, size | | (outbound buffer) + +-----------------+-------+--------------+----------------------+ + +Each buffer is started with a header and array of arguments. + +QTEE Transport Message supports four types of arguments: + +- Input Object (IO) is an object parameter to the current invocation + or callback request. +- Output Object (OO) is an object parameter from the current invocation + or callback request. +- Input Buffer (IB) is (offset, size) pair to the inbound or outbound region + to store parameter to the current invocation or callback request. +- Output Buffer (OB) is (offset, size) pair to the inbound or outbound region + to store parameter from the current invocation or callback request. + +The QTEE driver provides the qcomtee_object, which represents an object within +both QTEE and the kernel. To access any service in QTEE, a client needs to +invoke an instance of this object. Any structure intended to represent a service +for export to QTEE should include an instance of qcomtee_object:: + + struct driver_service { + struct qcomtee_object object; + ... + }; + + #define to_driver_service_object(o) container_of((o), struct driver_service, object) + + static int driver_service_dispatch(struct qcomtee_object *object, u32 op, + struct qcomtee_arg *args) + { + struct driver_service *so = to_driver_service_object(object); + + switch(op) { + case OBJECT_OP1: + ... + break; + default: + return -EINVAL; + } + } + + static void driver_service_object_release(struct si_object *object) + { + struct driver_service *so = to_driver_service_object(object); + kfree(so); + } + + struct si_object_operations driver_service_ops = { + .release = driver_service_object_release; + .dispatch = driver_service_dispatch; + }; + + void service_init(void) + { + struct driver_service *so = kzalloc(sizeof(*so), GFP_KERNEL); + + /* Initialize so->object as a callback object. */ + qcomtee_object_user_init(&so->object, QCOMTEE_OBJECT_TYPE_CB_OBJECT, + &driver_service_ops, "driver_service_object"); + + /* Invoke a QTEE object and pass/register 'so->object' with QTEE. */ + ... + } + module_init(service_init); + +The QTEE driver utilizes qcomtee_object to encapsulate userspace objects. When +a callback request is made, it translates into calling the dispatch operation. +For userspace objects, this is converted into requests accessible to callback +servers and available through generic TEE API IOCTLs. + +Picture of the relationship between the different components in the QTEE +architecture:: + + User space Kernel Secure world + ~~~~~~~~~~ ~~~~~~ ~~~~~~~~~~~~ + +--------+ +----------+ +--------------+ + | Client | |callback | | Trusted | + +--------+ |server | | Application | + /\ +----------+ +--------------+ + || +----------+ /\ /\ + || |callback | || || + || |server | || / + || +----------+ || +--------------+ + / /\ || | TEE Internal | + +-------+ || || | API | + | TEE | || || +--------+--------+ +--------------+ + | Client| || || | TEE | QTEE | | QTEE | + | API | / / | subsys | driver | | Trusted OS | + +-------+----------------+----+-------+----+-------------+--------------+ + | Generic TEE API | | QTEE MSG | + | IOCTL (TEE_IOC_*) | | SMCCC (QCOM_SCM_SMCINVOKE_*) | + +-----------------------------+ +---------------------------------+ + +References +========== + +[1] https://docs.qualcomm.com/bundle/publicresource/topics/80-70015-11/qualcomm-... + +[2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html + +[3] drivers/firmware/qcom/qcom_scm.c + +[4] drivers/tee/qcomtee/qcom_scm.c + +[5] drivers/tee/qcomtee/qcomtee_msg.h