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Add documentation for the Qualcomm TEE driver. Acked-by: Sumit Garg <sumit.garg@oss.qualcomm.com> Signed-off-by: Amirreza Zarrabi <amirreza.zarrabi@oss.qualcomm.com> Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
97 lines
4.7 KiB
ReStructuredText
97 lines
4.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=============================================
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QTEE (Qualcomm Trusted Execution Environment)
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=============================================
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The QTEE driver handles communication with Qualcomm TEE [1].
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The lowest level of communication with QTEE builds on the ARM SMC Calling
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Convention (SMCCC) [2], which is the foundation for QTEE's Secure Channel
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Manager (SCM) [3] used internally by the driver.
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In a QTEE-based system, services are represented as objects with a series of
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operations that can be called to produce results, including other objects.
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When an object is hosted within QTEE, executing its operations is referred
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to as "direct invocation". QTEE can also invoke objects hosted in the non-secure
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world using a method known as "callback request".
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The SCM provides two functions to support direct invocation and callback requests:
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- QCOM_SCM_SMCINVOKE_INVOKE: Used for direct invocation. It can return either
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a result or initiate a callback request.
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- QCOM_SCM_SMCINVOKE_CB_RSP: Used to submit a response to a callback request
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triggered by a previous direct invocation.
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The QTEE Transport Message [4] is stacked on top of the SCM driver functions.
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A message consists of two buffers shared with QTEE: inbound and outbound
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buffers. The inbound buffer is used for direct invocation, and the outbound
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buffer is used to make callback requests. This picture shows the contents of
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a QTEE transport message::
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+---------------------+
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+-----------------+-------+-------+------+--------------------------+
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| qcomtee_msg_ |object | buffer | |
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| object_invoke | id | offset, size | | (inbound buffer)
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+-----------------+-------+--------------+--------------------------+
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<---- header -----><---- arguments ------><- in/out buffer payload ->
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+-----------+
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+-----------------+-------+-------+------+----------------------+
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| qcomtee_msg_ |object | buffer | |
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| callback | id | offset, size | | (outbound buffer)
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+-----------------+-------+--------------+----------------------+
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Each buffer is started with a header and array of arguments.
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QTEE Transport Message supports four types of arguments:
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- Input Object (IO) is an object parameter to the current invocation
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or callback request.
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- Output Object (OO) is an object parameter from the current invocation
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or callback request.
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- Input Buffer (IB) is (offset, size) pair to the inbound or outbound region
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to store parameter to the current invocation or callback request.
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- Output Buffer (OB) is (offset, size) pair to the inbound or outbound region
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to store parameter from the current invocation or callback request.
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Picture of the relationship between the different components in the QTEE
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architecture::
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User space Kernel Secure world
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~~~~~~~~~~ ~~~~~~ ~~~~~~~~~~~~
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+--------+ +----------+ +--------------+
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| Client | |callback | | Trusted |
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+--------+ |server | | Application |
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/\ +----------+ +--------------+
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|| +----------+ /\ /\
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|| |callback | || ||
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|| |server | || \/
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|| +----------+ || +--------------+
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|| /\ || | TEE Internal |
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|| || || | API |
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\/ \/ \/ +--------+--------+ +--------------+
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+---------------------+ | TEE | QTEE | | QTEE |
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| libqcomtee [5] | | subsys | driver | | Trusted OS |
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+-------+-------------+--+----+-------+----+-------------+--------------+
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| Generic TEE API | | QTEE MSG |
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| IOCTL (TEE_IOC_*) | | SMCCC (QCOM_SCM_SMCINVOKE_*) |
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+-----------------------------+ +---------------------------------+
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References
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==========
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[1] https://docs.qualcomm.com/bundle/publicresource/topics/80-70015-11/qualcomm-trusted-execution-environment.html
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[2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
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[3] drivers/firmware/qcom/qcom_scm.c
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[4] drivers/tee/qcomtee/qcomtee_msg.h
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[5] https://github.com/quic/quic-teec
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