3.9. OP-TEE

Overview

OP-TEE is a Trusted Execution Environment (TEE) designed as a companion to a non-secure Linux kernel running on Arm Cortex-A cores using the TrustZone technology.

  1. Furthur information about it can be found at: https://optee.readthedocs.io/en/latest/general/about.html

  2. Official OP-TEE documentation: https://optee.readthedocs.io/en/latest

  3. OP-TEE advisory listing: https://github.com/OP-TEE/optee_os/security/advisories

The OP-TEE binary (bl32.bin/tee-pager_v2.bin) is bundled into tispl.bin and the following are the instructions to build:


Getting the OP-TEE Source Code

The pre-built OPTEE binary should be packaged in TI Processor SDK: <path-to-processor-sdk>/board-support/prebuilt-images/<optional-build-machine-name>/bl32.bin. Use this binary since it has been tested with TI Processor SDK.

If it is not possible to use pre-build binary, use the following:

$ git clone https://github.com/OP-TEE/optee_os.git
$ git checkout <hash>

Where <hash> is the OPTEE commit shown here: OP-TEE.


Setting up the toolchain paths

Before compiling any of the sources referenced in this document, set the cross compiler paths to the toolchains packaged in the Processor SDK [Recommended] as shown below. Refer to Yocto-built SDK Toolchains section for more details on usage.

host# export CROSS_COMPILE_64="${SDK_INSTALL_DIR}/linux-devkit/sysroots/x86_64-arago-linux/usr/bin/aarch64-oe-linux/aarch64-oe-linux-"
host# export SYSROOT_64="${SDK_INSTALL_DIR}/linux-devkit/sysroots/aarch64-oe-linux"
host# export CC_64="${CROSS_COMPILE_64}gcc --sysroot=${SYSROOT_64}"
host# export CROSS_COMPILE_32="${SDK_INSTALL_DIR}/k3r5-devkit/sysroots/x86_64-arago-linux/usr/bin/arm-oe-eabi/arm-oe-eabi-"

If the Processor SDK is not installed, the Arm GNU toolchains can be downloaded and setup. Refer to ARM toolchains section for more details on usage.

Building OP-TEE OS

  • Building the OPTEE image

    $ make CROSS_COMPILE="$CROSS_COMPILE_32" CROSS_COMPILE64="$CROSS_COMPILE_64" PLATFORM=k3-am64x CFG_ARM64_core=y

  • Building the OPTEE image with debug parameters

    $ make CROSS_COMPILE="$CROSS_COMPILE_32" CROSS_COMPILE64="$CROSS_COMPILE_64" PLATFORM=k3-am64x CFG_ARM64_core=y CFG_TEE_CORE_LOG_LEVEL=2 CFG_TEE_CORE_DEBUG=y

Secure Storage with RPMB (For HS)

OP-TEE provides secure storage functionality. TI SoCs with HS configuration have a KEK embedded in them that is programmed across OP-TEE instances that are distributed in a derived manner. Each HS device has its own HUK signing key (DKEK) which is different from other HS devices.

For enabling RPMB support along with secure storage, additional flags need to be passed to the build instructions. The information for the flags can be found here. https://optee.readthedocs.io/en/latest/architecture/secure_storage.html

There is a hybrid mode in which both the flags i.e CFG_REE_FS=y and CFG_RPMB_FS=y are enabled. This mode stores the state of the Secure Storage directory in RPMB partition to check for the integrity of the data present in it. It is the recommended way.

E.g. For enabling hybrid mode of RPMB along with REE_FS

$ make CROSS_COMPILE64="$CROSS_COMPILE_64" PLATFORM=k3-am64x CFG_ARM64_core=y CFG_REE_FS=y CFG_RPMB_FS=y

OPTEE-client also needs to be updated to enable the use of real emmc instead of the virtual emmc that is enabled by default

Getting OP-TEE Client source code

$ git clone https://github.com/OP-TEE/optee_client

Building OP-TEE Client with RPMB support

$ make CROSS_COMPILE="$CROSS_COMPILE_64" PLATFORM=k3 CFG_TEE_SUPP_LOG_LEVEL=2 RPMB_EMU=0 CFG_ARM64_core=y

Now update optee-client binary and libraries on your SD card with the generated ones in out/export/usr folder


Building u-boot with OP-TEE OS

As of Processor SDK 9.0, the signing functionality earlier provided by the TI Security Development Package, has been integrated within U-Boot itself. This means tee-pager_v2.bin does not need to be signed before being packaged in tispl.bin in U-Boot for HS devices.

Expected binary output

  1. Generated binary: tee-pager_v2.bin

  2. Binary saved saved in: <path-to-optee>/out/arm-plat-k3/core

Integrate binary output into U-boot

  1. Go to u-boot folder <path-to-u-boot>

  2. Re-build U-boot with A72/A53 instructions found under: Build U-Boot, but with the TEE parameter pointing to the newly built tee-pager_v2.bin. i.e. TEE=<path-to-optee>/out/arm-plat-k3/core/tee-pager_v2.bin

Note

tee-pager_v2.bin may be called bl32.bin in other documentation.