How to configure OP-TEE

Applicable for STM32MP13x lines, STM32MP15x lines

1 Purpose[edit]

This article describes the configuration and process used for building several OP-TEE components from sources and deploying them the target.

The build example is based on the OpenSTLinux Developer Package or Distribution Package, and also presents build instructions for a bare environment.

2 Overview[edit]

OP-TEE is a trusted execution environment for Arm®v7-A and Arm®v8-A platforms. OP-TEE is made of several components described in OP-TEE architecture overview.

OP-TEE components generate boot images and files stored in the filesystem embedded in the target.

  • OP-TEE OS generates 3 boot image files to be loaded in the platform boot media, in the predefined partitions. The generated boot images include a STM32 binary header enabling the use of the authenticated boot and flash programming facilities.
  • OP-TEE client (package optee_client) can be built to generate non-secure services for the OP-TEE OS. The files generated from optee_client build are stored in the embedded filesystem.
  • OP-TEE project releases other packages intended for test and demonstration. These can be built and embedded in the target filesystem. Building optee_examples and optee_test generates client and trusted applications together with libraries which are all stored in the target filesystem. Note the OP-TEE Linux driver is built into the Linux kernel image and is part of the OP-TEE ecosystem.

OP-TEE can be embedded as BL32 in the STM32 MPU platforms for the ST trusted configuration.

Warning white.png Warning
OP-TEE boot images must be embedded in the FIP binary that is loaded by BL2 and can be automatically authentified

3 OP-TEE core configuration[edit]

OP-TEE services STM32MP13x lines More info.png STM32MP15x lines More info.png
(OP-TEE in SYSRAM)		 STM32MP15x lines More info.png
(OP-TEE in DDR)
SCMI services ✓ ✓ ✓
PSCI services ✓ ✓ ✓
Oscillator calibration service ✓ ✓ ✓
Random generation service ✓ ✓ ✓
Wakeup source management ✓ ✓ ✓
Power Domain service ✓ ✓ ✓
OTP access services ✓ ✓ ✓
NVMEM provisioning services ✓ ✓
User Trusted application support ✓ ✓
Trustworthiness of secure services ✓ ✓
OPP request management ✓
Remote proc services ✓

3.1 SCMI services[edit]

SCMI services STM32MP13x lines More info.png STM32MP15x lines More info.png
(OP-TEE in SYSRAM)		 STM32MP15x lines More info.png
(OP-TEE in DDR)
Clock management ✓ ✓ ✓
Reset management ✓ ✓ ✓
Performance management ✓
Regulator management ✓ ✓ ✓

3.2 PSCI services[edit]

PSCI services STM32MP13x lines More info.png STM32MP15x lines More info.png
(OP-TEE in SYSRAM)		 STM32MP15x lines More info.png
(OP-TEE in DDR)
System reset ✓ ✓ ✓
CPU hotplug ✓ ✓ ✓
Low power ✓ ✓ ✓

3.3 STM32MP13x lines More info.png[edit]

OP-TEE OS is loaded in DDR. Thanks to DDRMCE, the DDR area is encrypted.

3.4 STM32MP15x lines More info.png[edit]

Warning white.png Warning
Enabling OP-TEE secure services in STM32MP15x lines More info.png for ecosystem release ≥ v5.0.0 More info.png

Before ecosystem release v5.0.0 More info.png , OP-TEE for STM32MP15x lines More info.png default configuration builds OP-TEE so that the firmware and the Trusted Applications execute in secure SYSRAM insternal secure memory.
With ecosystem release ≥ v5.0.0 More info.png OP-TEE OS for STM32MP15x lines More info.png default configuration makes it loaded in DDR, relaxed from hardware contraints of running in the secure SYSRAM. Because the DDR is not encrypted, OP-TEE cannot enforce trustworthiness of its secure services. Therefore this default configuration disables OP-TEE support for Trusted Applications and secure services. This default configuration only embeds support for power management and system services.

From ecosystem release v5.0.0 More info.png , OP-TEE for STM32MP15x lines More info.png, one can enable back OP-TEE secure services by changing the components build configuration switches so that OP-TEE executes in the secure SYSRAM, refer to Details on build directives.

When OP-TEE is running in SYSRAM:

OP-TEE OS requires more than 256Ko RAM to execute. STM32MP15x lines More info.png SYSRAM is only 256Ko large therefore OP-TEE core, when executing from SYSRAM must enable its pager mode (configuration switch CFG_WITH_PAGER=y) to extend secure memory using virtual memory means and paging on demand mechanisms to save secure data into DDR, protected by hash tables and software encryption keys.

When so, OP-TEE boot image is made of 2 binary images: one (the unpaged part) is loaded at the beginning of the SYSRAM by the FSBL, the second (the pageable part) is loaded in DDR by the FSBL, in a DDR area that can be accessed by the CPU secure world.

OP-TEE OS manages low power mode by saving an encrypted image of the SYSRAM content in DDR before it is suspended. OP-TEE restores this content back into the SYSRAM when it resumes from the suspended state. This sequence is achieved using CPU instructions and encryption keys saved in the secure and retained backup SRAM.

For more information on OP-TEE's pager implementation and integration, one can refer to the OP-TEE documenation related to pager [1]

4 Build with the Distribution Package[edit]

The Distribution Package provides means to build the following OP-TEE components from their related bitbake target: 

 bitbake optee-os-stm32mp                # OP-TEE core firmware
 bitbake optee-os-sdk-stm32mp            # OP-TEE development kit for Trusted Applications
 bitbake optee-client                    # OP-TEE client
 bitbake optee-test                      # OP-TEE test suite (optional)
 bitbake optee-examples                  # TA and CA examples

Distribution Package build process includes fetching the source files, compiling them and installing them to the target images.

The Yocto recipes for the OP-TEE packages can be found in:

meta-st/meta-st-stm32mp/recipes-security/optee/optee-os-stm32mp*
meta-st/meta-st-openstlinux/recipes-security/optee/optee-client*
meta-st/meta-st-openstlinux/recipes-security/optee/optee-examples*
meta-st/meta-st-openstlinux/recipes-security/optee/optee-test*

5 Build with the Developer Package or a Bare Environment[edit]

Both Developer Package and bare build environments expect you to fetch/download the OP-TEE package source file trees in order to build the embedded binary images.

The instruction set below assumes all OP-TEE package source trees are available in the base directory referred as <sources>/. The source files are available from the github repositories: 

 cd <sources>/
 git clone https://github.com/STMicroelectronics/optee_os.git
 git clone https://github.com/OP-TEE/optee_client.git
 git clone https://github.com/OP-TEE/optee_test.git
 git clone https://github.com/linaro-swg/optee_examples.git
 ls -1 <sources>/
optee_client
optee_examples
optee_os
optee_test


Warning white.png Warning
Pay attention to use a consistent tag version for all optee components eg 3.12.0 for DV3.1
Warning white.png Warning
The STM32 MPU platform may not be fully merged in the official OP-TEE repository [2] hence the URL provided above refers to the ST distribution [3]


5.1 Initialize the cross compile environment[edit]

The compilation toolchain provided by the Developer Package can be used, refer to Setup Cross Compile Environment.

Alternatively other bare toolchains can be used to build the OP-TEE secure parts. In such case, the instructions below expect the toolchain to be part of the PATH and its prefix is defined by CROSS_COMPILE. One can use something like: 

 export PATH=<path-to-toolchain>:$PATH
 export CROSS_COMPILE=<toolchain-prefix>-

5.2 Build OP-TEE OS[edit]

5.2.1 Developer Package SDK[edit]

The OP-TEE OS can be built from the Developer Package Makefile.sdk script that is present in the tarball. It automatically sets the proper configuration for the OP-TEE OS build. To build from shell command:

 make -f $PWD/../Makefile.sdk CFG_EMBED_DTB_SOURCE_FILE=<board_dts_file_name>.dts

5.2.2 Bare Environment[edit]

Alternatively one can also build OP-TEE OS based a bare cross compilation toolchains, for example for the stm32mp157c-ev1 board: 

 cd <optee-os>
 make PLATFORM=stm32mp1 \
           CFG_EMBED_DTB_SOURCE_FILE=stm32mp157c-ev1.dts \
           CFG_TEE_CORE_LOG_LEVEL=2 O=build all

5.2.3 Generated Files[edit]

The 3 OP-TEE boot images are generated at following paths: 

<optee-os>/build/core/tee-header_v2.bin
<optee-os>/build/core/tee-pageable_v2.bin
<optee-os>/build/core/tee-pager_v2.bin

One can get the configuration directives used for the build are available in this file: 

<optee-os>/build/conf.mk

The build also generates a development kit used to build Trusted Application binaries: 

<optee-os>/build/export-ta_arm32/

5.2.4 Details on build directives[edit]

Mandatory directives to build OP-TEE OS:

  • PLATFORM=<platform>
    • Ex: PLATFORM=stm32mp1
  • CFG_EMBED_DTB_SOURCE_FILE=<device-tree-source-file>: in-tree (core/arch/arm/dts/ ) device tree filename with its .dts extension.
    • Ex: CFG_EMBED_DTB_SOURCE_FILE=stm32mp157f-dk2.dts


OP-TEE generic optional directives commonly used, described in OP-TEE OS mk/config.mk file:

  • CFG_CORE_HEAP_SIZE=<VALUE>: define the byte size of OP-TEE core memory allocation pool
  • CFG_NUM_THREADS=<VALUE>: define the number of TEE threads provisioned in OP-TEE
  • CFG_REE_FS={n|y}: disable/enable OP-TEE REE filsystem based secure storage area
  • CFG_RPMB_FS={n|y}: disable/enable OP-TEE eMMC/RPMB based secure storage area
  • CFG_RPMB_FS_DEV_ID=<VALUE>: define the mmcblk block device used by REE for eMMC/RPMB accesses
    (e.g. "1" on stm32mp157x-ev1 boards)
  • CFG_WITH_USER_TA={n|y}: disable/enable support for Trusted Applications in OP-TEE secure memory (default is y)


OP-TEE generic optional debugging and test directives commonly used, described in OP-TEE OS mk/config.mk file:

  • CFG_TEE_CORE_DEBUG={n|y}: disable/enable debug support
  • CFG_TEE_CORE_LOG_LEVEL={0|1|2|3|4}: define OP-TEE core trace level (0: no trace, 4: overflow of traces) (default is 2: info)
  • CFG_TEE_CORE_TA_LEVEL={0|1|2|3|4}: define OP-TEE Trusted Applications (TAs) trace level (default is 1: error)
  • CFG_TEE_CORE_TA_TRACE={n|y}: disable/enable TAs trace message at define OP-TEE core level (default is y)
  • CFG_UNWIND={n|y}: disable/enable stack unwind debug trace messages
  • CFG_ENABLE_EMBEDDED_TESTS={n|y}; disable/enable embedded test, used by xtest tool (default is y)
  • CFG_WITH_STATS={n|y}: disable/enable OP-TEE statistics retrieve from the Stats PTA service.
  • CFG_WERROR={n|y}: disable/enable build error trigger on OP-TEE build warning occurences.
  • CFG_TA_GPROF_SUPPORT={n|y}: disable/enable profiling of Trusted Application implementation based on gprof standard tool
  • CFG_FTRACE_SUPPORT={n|y}: disable/enable function trace support in Trusted Applications based on ftrace standard tool
  • CFG_SYSCALL_FTRACE={n|y}: disable/enable support for ftrace syscall graph generation


OP-TEE optional directives commonly used on STM32MP1 series:

  • CFG_STM32_EARLY_CONSOLE_UART={0|1|2|...}: define the USART instance used for early console trace messages (default is 4)
  • CFG_STM32_BSEC_WRITE={n|y}: disable/enable the program/write fuses capabilities (default n to avoid briking the chip)


OP-TEE optional directives specific to STM32MP15x lines More info.png ecosystem release ≥ v5.0.0 More info.png :

  • CFG_STM32MP1_OPTEE_IN_SYSRAM={n|y}: See warning section below and STM32MP15x lines for details (default is n).
    Note that when CFG_STM32MP1_OPTEE_IN_SYSRAM=n, CFG_WITH_USER_TA default value is n,
    and when CFG_STM32MP1_OPTEE_IN_SYSRAM=y, CFG_WITH_USER_TA default value is y.
  • CFG_STM32MP15_HUK={n|y}: disable/enable reading of OP-TEE's HUK (Hardware Unique Key) from BSEC fuses.
  • CFG_STM32_HUK_FROM_DT={n|y}: disable/enable reading of HUK location in BSEC fuses from OP-TEE's embedded Device Tree.
  • CFG_STM32_HUK_TESTKEY={n|y}: disable/enable use of a test (default is y)
    Supersedes CFG_OTP_HW_TESTKEY used in before ecosystem release v5.0.0 More info.png .


Info white.png Information

For ecosystem release ≤ v3.0.0 compatibility:
It is still possible to generate the the STM32 binary files with an option flag:
CFG_STM32MP15x_STM32IMAGE=1: Generate the STM32 files for ecosystem release ≤ v3.0.0 compatibility.


Warning white.png Warning

"To enable OP-TEE secure service for STM32MP15x lines More info.png on ecosystem release ≥ v5.0.0 More info.png , one must configure OP-TEE to execute in secure SYSRAM. TF-A boot loader must also be configured to load OP-TEE in internal SYSRAM, not is DDR.
To make OP-TEE for STM32MP15x lines More info.png to execute in SYSRAM, one shall:

  • enable OP-TEE configuration switch CFG_STM32MP1_OPTEE_IN_SYSRAM=y
  • enable TF-A configuration switch STM32MP1_OPTEE_IN_SYSRAM=1 for both TF-A BL2 and TF-A FIP images.

Note: internal memory size constrains the debug support level that can be provided.

5.2.5 Troubleshoot[edit]

The Developer Package toolchain may report dependency error in the traces such as: 

 make PLATFORM=stm32mp1 ...
arm-ostl-linux-gnueabi-ld.bfd: unrecognized option '-Wl,-O1' 
arm-ostl-linux-gnueabi-ld.bfd: use the --help option for usage information
core/arch/arm/kernel/link.mk:165: recipe for target 'build/arm-plat-stm32mp1/core/tee.elf' failed
make: *** [build/arm-plat-stm32mp1/core/tee.elf] Error 1

This is linked to default CFLAGS and LDFLAGS exported by SDK. Just remove them from the environment and rebuild 

 unset -v CFLAGS LDFLAGS

Other reported issues: 

 make PLATFORM=stm32mp1 ...
arm-openstlinux_weston-linux-gnueabi-ld.bfd: cannot find libgcc.a: No such file or directory

To overcome the issue, add the directive CFLAGS32=--sysroot=$SDKTARGETSYSROOT. For example: 

 cd <optee-os>
 make PLATFORM=stm32mp1 \
           CFG_EMBED_DTB_SOURCE_FILE=stm32mp157c-ev1.dts \
           CFG_TEE_CORE_LOG_LEVEL=2 \
           CFLAGS32=--sysroot=${SDKTARGETSYSROOT} \
           O=build all

5.3 Build commands for other OP-TEE components[edit]

This section describes how the several OP-TEE components (excluding OP-TEE OS described in above section) can be built. All those components generate files targeting the embedded Linux OS based filesystem (i.e the rootfs). These files are the secure Trusted Applications (TAs) binaries as well as non-secure Client Applications (CAs), libraries and test files.

There are several ways to build the OP-TEE components. The examples given below refer to OP-TEE client, test and examples source file tree paths as <optee-client>, <optee-test> and <optee-examples>.

Building these components expect, at least for the trusted applications, that the OP-TEE OS was built and the generated TA development kit is available at <optee-os>/build/export-ta_arm32/.

It is recommended to use CMake for building the Linux userland part whereas secure world binaries (TAs) must be build from their GNU makefiles as the OP-TEE project has not yet ported the secure world binaries build process over CMake.

5.3.1 Build the secure components[edit]

Build the TAs: This step expects OP-TEE OS is built to generate the 32bit TA development kit. Assuming OP-TEE OS was built at path <optee-os>/build, the TA development kit is available from path <optee-os>/build/export-ta_arm32/.

Instructions below build and copy the Trusted Application binaries to a local ./target/ directory that can be used to populate the target filesystem. 

 export TA_DEV_KIT_DIR=$PWD/optee_os/build/export-ta_arm32
 mkdir -p ./target/lib/optee_armtz
 for f in optee_test/ta/*/Makefile; do \
            make -C `dirname $f` O=build; \
            cp -f `dirname $f`/build/*.ta ./target/lib/optee_armtz; \
      done

Content in local directory ./target/ are the TA binary files: 

 tree target/
target
└── lib
  └── optee_armtz
   ├── 614789f2-39c0-4ebf-b235-92b32ac107ed.ta
   ├── 731e279e-aafb-4575-a771-38caa6f0cca6.ta
   └── (...)

These files need to be copied to the the target filesystem.

5.3.2 Build the non-secure components[edit]

Download the OP-TEE source files in a base directory and create a CMakeLists.txt file in the base directory that lists all package to be built through CMake. For example: 

 ls
optee_client
optee_examples
optee_os
optee_test
CMakeLists.txt
 cat CMakeLists.txt
add_subdirectory (optee_client)
add_subdirectory (optee_test)
add_subdirectory (optee_examples)

From base directory, run cmake then make. The example below also creates the tree file system ./target/ that is populated with files generated that need to be installed in the target file system.
Note this examples also sets the toolchain environment: 

 cmake -DOPTEE_TEST_SDK=$PWD/optee_os/build/export-ta_arm32 \
            -DCMAKE_INSTALL_PREFIX=  -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=y
 make
 make DESTDIR=target install

Note the empty CMAKE_INSTALL_PREFIX value to get thing installed from root /, not from /usr/. DESTDIR=target makes the embedded files be populated in the local ./target/ directory.

Note also that stm32mp1 expects tool tee-supplicant to be located in directory /usr/bin whereas CMake installs it in directory /usr/sbin. To overcome this issue, one can build a link to the effective location, i.e: 

 ln -s ../bin/tee-supplicant target/sbin/tee-supplicant

Once done, local directory ./target/ contains the files to be copied in the target filesystem. 

 tree target/
target/
├── bin
│   ├── benchmark
│   ├── optee_example_acipher
│   ├── optee_example_aes
│   ├── optee_example_hello_world
│   ├── optee_example_hotp
│   ├── optee_example_random
│   ├── optee_example_secure_storage
│   ├── tee-supplicant
│   └── xtest
├── include
│   ├── tee_bench.h
│   ├── tee_client_api_extensions.h
│   ├── tee_client_api.h
│   └── teec_trace.h
├── lib
│   ├── libteec.so -> libteec.so.1
│   ├── libteec.so.1 -> libteec.so.1.0.0
│   └── libteec.so.1.0.0
│   └── optee_armtz
│       └── (...)                 # This directory was previously filled with TAs
└── sbin
    └── tee-supplicant -> ../bin/tee-supplicant

6 Update OP-TEE boot images[edit]

OP-TEE boot images are part of the FIP binary.
The next step to deploy the OP-TEE OS is to update the FIP binary following the FIP update process.

7 Update OP-TEE Linux files[edit]

7.1 Update on board[edit]

The other OP-TEE images are stored in the target filesystem.

For example, if using an SD card as target boot media, the card can be plugged in its PC card reader and the images copied. The files can be simply copied into the mounted rootfs.

7.2 Update in a SD card[edit]

The OP-TEE files that need to be copied to the target filesystem were installed in a local directory ./target/.

They can now be copied to the target SD card rootfs partition once the SD card is plugged to the host computer and its filesystems are mounted in the host, i.e 

 cp -ar target/* /media/$USERNAME/rootfs/

8 Update your boot device (including SD card on the target)[edit]

Refer to the STM32CubeProgrammer documentation to update your target.

9 References[edit]

  1. ↑ https://optee.readthedocs.io/en/latest/architecture/core.html#pager
  2. ↑ https://github.com/OP-TEE/optee_os
  3. ↑ https://github.com/STMicroelectronics/optee_os



Open portable trusted execution environment

Arm® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere. Arm logo.png

Operating system

Linux® is a registered trademark of Linus Torvalds.

Boot loader stage 3-2

Microprocessor unit

Boot loader stage 2

Doubledata rate (memory domain)

Operating performance point (link to voltage and frequency scaling)

System control and management interface

Power state coordination interface

Central processing unit

Random access memory (Early computer memories generally hadserial access. Memories where any given address can be accessed when desired were then called "random access" to distinguish them from the memories where contents can only be accessed in a fixed order. The term is used today for volatile random-acces ssemiconductor memories.)

First stage boot loader

Trusted application

Software development kit (A programming package that enables a programmer to develop applications for a specific platform.)

Device tree binary (or Blob)

Trusted execution environment

File system or filesystem, method and data structure that the operating system uses to control how data is stored and retrieved -NEW

Former spelling for e•MMC ('e' in italic)

Pseudo Trusted Application

Universal asynchronous receiver/transmitter

Universal synchronous/asynchronous receiver/transmitter

Boot and Security and OTP control

Hardware unique key

Device tree

One time programmed

Trusted firmware for Arm® Cortex®-A

Firmware image package is a packaging format used by TF-A

SD memory card (https://www.sdcard.org)

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