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91 lines
4.3 KiB
ReStructuredText
91 lines
4.3 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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=============================================
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AMD-TEE (AMD's Trusted Execution Environment)
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=============================================
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The AMD-TEE driver handles the communication with AMD's TEE environment. The
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TEE environment is provided by AMD Secure Processor.
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The AMD Secure Processor (formerly called Platform Security Processor or PSP)
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is a dedicated processor that features ARM TrustZone technology, along with a
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software-based Trusted Execution Environment (TEE) designed to enable
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third-party Trusted Applications. This feature is currently enabled only for
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APUs.
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The following picture shows a high level overview of AMD-TEE::
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x86 |
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User space (Kernel space) | AMD Secure Processor (PSP)
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~~~~~~~~~~ ~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~~~~~~~~~
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+--------+ | +-------------+
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| Client | | | Trusted |
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+--------+ | | Application |
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/\ | +-------------+
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|| | /\
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|| | \/
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|| | +----------+
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|| | | TEE |
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|| | | Internal |
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\/ | | API |
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+---------+ +-----------+---------+ +----------+
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| TEE | | TEE | AMD-TEE | | AMD-TEE |
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| Client | | subsystem | driver | | Trusted |
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| API | | | | | OS |
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+---------+-----------+----+------+---------+---------+----------+
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| Generic TEE API | | ASP | Mailbox |
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| IOCTL (TEE_IOC_*) | | driver | Register Protocol |
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+--------------------------+ +---------+--------------------+
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At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the
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CPU to PSP mailbox register to submit commands to the PSP. The format of the
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command buffer is opaque to the ASP driver. It's role is to submit commands to
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the secure processor and return results to AMD-TEE driver. The interface
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between AMD-TEE driver and AMD Secure Processor driver can be found in [1].
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The AMD-TEE driver packages the command buffer payload for processing in TEE.
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The command buffer format for the different TEE commands can be found in [2].
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The TEE commands supported by AMD-TEE Trusted OS are:
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* TEE_CMD_ID_LOAD_TA - loads a Trusted Application (TA) binary into
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TEE environment.
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* TEE_CMD_ID_UNLOAD_TA - unloads TA binary from TEE environment.
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* TEE_CMD_ID_OPEN_SESSION - opens a session with a loaded TA.
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* TEE_CMD_ID_CLOSE_SESSION - closes session with loaded TA
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* TEE_CMD_ID_INVOKE_CMD - invokes a command with loaded TA
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* TEE_CMD_ID_MAP_SHARED_MEM - maps shared memory
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* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory
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AMD-TEE Trusted OS is the firmware running on AMD Secure Processor.
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The AMD-TEE driver registers itself with TEE subsystem and implements the
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following driver function callbacks:
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* get_version - returns the driver implementation id and capability.
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* open - sets up the driver context data structure.
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* release - frees up driver resources.
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* open_session - loads the TA binary and opens session with loaded TA.
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* close_session - closes session with loaded TA and unloads it.
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* invoke_func - invokes a command with loaded TA.
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cancel_req driver callback is not supported by AMD-TEE.
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The GlobalPlatform TEE Client API [3] can be used by the user space (client) to
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talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening
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a session, invoking commands and closing session with TA.
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References
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==========
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[1] include/linux/psp-tee.h
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[2] drivers/tee/amdtee/amdtee_if.h
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[3] http://www.globalplatform.org/specificationsdevice.asp look for
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"TEE Client API Specification v1.0" and click download.
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