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linux-7.2.3/Documentation/tee/amd-tee.rst
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.. SPDX-License-Identifier: GPL-2.0
=============================================
AMD-TEE (AMD's Trusted Execution Environment)
=============================================
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 register 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 [1].
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 [2].
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 [3] 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 closing session with TA.
References
==========
[1] include/linux/psp-tee.h
[2] drivers/tee/amdtee/amdtee_if.h
[3] http://www.globalplatform.org/specificationsdevice.asp look for
"TEE Client API Specification v1.0" and click download.
linux-7.2.3/Documentation/tee/index.rst
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.. SPDX-License-Identifier: GPL-2.0
=============
TEE Subsystem
=============
.. toctree::
:maxdepth: 1
tee
op-tee
amd-tee
ts-tee
qtee
linux-7.2.3/Documentation/tee/op-tee.rst
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.. SPDX-License-Identifier: GPL-2.0
====================================================
OP-TEE (Open Portable Trusted Execution Environment)
====================================================
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::
User space Kernel Secure world
~~~~~~~~~~ ~~~~~~ ~~~~~~~~~~~~
+--------+ +-------------+
| Client | | Trusted |
+--------+ | Application |
/\ +-------------+
|| +----------+ /\
|| |tee- | ||
|| |supplicant| \/
|| +----------+ +-------------+
\/ /\ | TEE Internal|
+-------+ || | API |
+ TEE | || +--------+--------+ +-------------+
| Client| || | TEE | OP-TEE | | OP-TEE |
| API | \/ | subsys | driver | | Trusted OS |
+-------+----------------+----+-------+----+-----------+-------------+
| Generic TEE API | | OP-TEE MSG |
| IOCTL (TEE_IOC_*) | | SMCCC (OPTEE_SMC_CALL_*) |
+-----------------------------+ +------------------------------+
RPC (Remote Procedure Call) are requests from secure world to kernel driver
or tee-supplicant. An RPC is identified by a special range of SMCCC return
values from OPTEE_SMC_CALL_WITH_ARG. RPC messages which are intended for the
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.
OP-TEE device enumeration
-------------------------
OP-TEE provides a pseudo Trusted Application: drivers/tee/optee/device.c in
order to support device enumeration. In other words, OP-TEE driver invokes this
application to retrieve a list of Trusted Applications which can be registered
as devices on the TEE bus.
OP-TEE notifications
--------------------
There are two kinds of notifications that secure world can use to make
normal world aware of some event.
1. Synchronous notifications delivered with ``OPTEE_RPC_CMD_NOTIFICATION``
using the ``OPTEE_RPC_NOTIFICATION_SEND`` parameter.
2. Asynchronous notifications delivered with a combination of a non-secure
edge-triggered interrupt and a fast call from the non-secure interrupt
handler.
Synchronous notifications are limited by depending on RPC for delivery,
this is only usable when secure world is entered with a yielding call via
``OPTEE_SMC_CALL_WITH_ARG``. This excludes such notifications from secure
world interrupt handlers.
An asynchronous notification is delivered via a non-secure edge-triggered
interrupt to an interrupt handler registered in the OP-TEE driver. The
actual notification value are retrieved with the fast call
``OPTEE_SMC_GET_ASYNC_NOTIF_VALUE``. Note that one interrupt can represent
multiple notifications.
One notification value ``OPTEE_SMC_ASYNC_NOTIF_VALUE_DO_BOTTOM_HALF`` has a
special meaning. When this value is received it means that normal world is
supposed to make a yielding call ``OPTEE_MSG_CMD_DO_BOTTOM_HALF``. This
call is done from the thread assisting the interrupt handler. This is a
building block for OP-TEE OS in secure world to implement the top half and
bottom half style of device drivers.
OPTEE_INSECURE_LOAD_IMAGE Kconfig option
----------------------------------------
The OPTEE_INSECURE_LOAD_IMAGE Kconfig option enables the ability to load the
BL32 OP-TEE image from the kernel after the kernel boots, rather than loading
it from the firmware before the kernel boots. This also requires enabling the
corresponding option in Trusted Firmware for Arm. The Trusted Firmware for Arm
documentation [6] explains the security threat associated with enabling this as
well as mitigations at the firmware and platform level.
There are additional attack vectors/mitigations for the kernel that should be
addressed when using this option.
1. Boot chain security.
* Attack vector: Replace the OP-TEE OS image in the rootfs to gain control of
the system.
* Mitigation: There must be boot chain security that verifies the kernel and
rootfs, otherwise an attacker can modify the loaded OP-TEE binary by
modifying it in the rootfs.
2. Alternate boot modes.
* Attack vector: Using an alternate boot mode (i.e. recovery mode), the
OP-TEE driver isn't loaded, leaving the SMC hole open.
* Mitigation: If there are alternate methods of booting the device, such as a
recovery mode, it should be ensured that the same mitigations are applied
in that mode.
3. Attacks prior to SMC invocation.
* Attack vector: Code that is executed prior to issuing the SMC call to load
OP-TEE can be exploited to then load an alternate OS image.
* Mitigation: The OP-TEE driver must be loaded before any potential attack
vectors are opened up. This should include mounting of any modifiable
filesystems, opening of network ports or communicating with external
devices (e.g. USB).
4. Blocking SMC call to load OP-TEE.
* Attack vector: Prevent the driver from being probed, so the SMC call to
load OP-TEE isn't executed when desired, leaving it open to being executed
later and loading a modified OS.
* Mitigation: It is recommended to build the OP-TEE driver as builtin driver
rather than as a module to prevent exploits that may cause the module to
not be loaded.
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.
[6] https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model.html
linux-7.2.3/Documentation/tee/qtee.rst
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.. 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.
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 also invoke objects hosted in the non-secure
world using a method known as "callback request".
The SCM provides two functions to support direct invocation and callback requests:
- QCOM_SCM_SMCINVOKE_INVOKE: Used for direct invocation. It can return either
a result or initiate a callback request.
- QCOM_SCM_SMCINVOKE_CB_RSP: Used to submit a response to a callback request
triggered by a previous direct invocation.
The QTEE Transport Message [4] 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.
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 | QTEE | | QTEE |
| libqcomtee [5] | | 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-trusted-execution-environment.html
[2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
[3] drivers/firmware/qcom/qcom_scm.c
[4] drivers/tee/qcomtee/qcomtee_msg.h
[5] https://github.com/quic/quic-teec
linux-7.2.3/Documentation/tee/tee.rst
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.. SPDX-License-Identifier: GPL-2.0
===================================
TEE (Trusted Execution Environment)
===================================
This document describes the TEE subsystem in Linux.
Overview
========
A TEE 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 subsystem deals with:
- Registration of TEE drivers
- Managing shared memory between Linux and the TEE
- Providing a generic API to the TEE
linux-7.2.3/Documentation/tee/ts-tee.rst
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.. SPDX-License-Identifier: GPL-2.0
=================================
TS-TEE (Trusted Services project)
=================================
This driver provides access to secure services implemented by Trusted Services.
Trusted Services [1] is a TrustedFirmware.org project that provides a framework
for developing and deploying device Root of Trust services in FF-A [2] S-EL0
Secure Partitions. The project hosts the reference implementation of the Arm
Platform Security Architecture [3] for Arm A-profile devices.
The FF-A Secure Partitions (SP) are accessible through the FF-A driver [4] which
provides the low level communication for this driver. On top of that the Trusted
Services RPC protocol is used [5]. To use the driver from user space a reference
implementation is provided at [6], which is part of the Trusted Services client
library called libts [7].
All Trusted Services (TS) SPs have the same FF-A UUID; it identifies the TS RPC
protocol. A TS SP can host one or more services (e.g. PSA Crypto, PSA ITS, etc).
A service is identified by its service UUID; the same type of service cannot be
present twice in the same SP. During SP boot each service in the SP is assigned
an "interface ID". This is just a short ID to simplify message addressing.
The generic TEE design is to share memory at once with the Trusted OS, which can
then be reused to communicate with multiple applications running on the Trusted
OS. However, in case of FF-A, memory sharing works on an endpoint level, i.e.
memory is shared with a specific SP. User space has to be able to separately
share memory with each SP based on its endpoint ID; therefore a separate TEE
device is registered for each discovered TS SP. Opening the SP corresponds to
opening the TEE device and creating a TEE context. A TS SP hosts one or more
services. Opening a service corresponds to opening a session in the given
tee_context.
Overview of a system with Trusted Services components::
User space Kernel space Secure world
~~~~~~~~~~ ~~~~~~~~~~~~ ~~~~~~~~~~~~
+--------+ +-------------+
| Client | | Trusted |
+--------+ | Services SP |
/\ +-------------+
|| /\
|| ||
|| ||
\/ \/
+-------+ +----------+--------+ +-------------+
| libts | | TEE | TS-TEE | | FF-A SPMC |
| | | subsys | driver | | + SPMD |
+-------+----------------+----+-----+--------+-----------+-------------+
| Generic TEE API | | FF-A | TS RPC protocol |
| IOCTL (TEE_IOC_*) | | driver | over FF-A |
+-----------------------------+ +--------+-------------------------+
References
==========
[1] https://www.trustedfirmware.org/projects/trusted-services/
[2] https://developer.arm.com/documentation/den0077/
[3] https://www.arm.com/architecture/security-features/platform-security
[4] drivers/firmware/arm_ffa/
[5] https://trusted-services.readthedocs.io/en/v1.0.0/developer/service-access-protocols.html#abi
[6] https://git.trustedfirmware.org/TS/trusted-services.git/tree/components/rpc/ts_rpc/caller/linux/ts_rpc_caller_linux.c?h=v1.0.0
[7] https://git.trustedfirmware.org/TS/trusted-services.git/tree/deployments/libts/arm-linux/CMakeLists.txt?h=v1.0.0