Trusted Substrate


June 2022

April 2022

  • Reworked capsule updates for U-Boot. The previous implementation wasn’t adhering to the EFI spec

  • Bumped all meta-ts supported boards to the latest stable U-Boot 2022.04

  • Fixed all the remaining SystemReady Interface Extensions failures in U-Boot

March 2022

  • U-Boot fixes in EFI. The Arm security ACS should pass all tests now

  • Fault mitigation patterns investigation for OP-TEE TAs

  • Blogposts on FF-A support within OP-TEE

  • Basic TPM2 support added into OP-TEE

February 2022

  • Created patches for SystemReady-ACS for arm7 (stm32mp1 tested)

  • Fixed UEFI Secure boot with intermediate certificates

  • Updated meta-ts, consumers can now define their own set of keys to create
    the EFI security database

  • Menu driven boot device selection for U-Boot posted in ML. Patches are under review

  • Added support for Xilinx kv260 AI vision starter kit



This calendar is displayed using UTC timezone with no DST offsets.

Project Contacts

About this project

Trusted Substrate is a meta-layer in OpenEmbedded aimed toward board makers who want to produce an Arm SystemReady compliant firmware and ensure consistent behaviour, tamper protection and common features across platforms. In a nutshell, TrustedSubstrate is building firmware for devices which verifies the running software hasn’t been tampered with. It does so by utilizing a well-known set of standards.

  • UEFI secure boot enabled by default UEFI Secure Boot is a verification mechanism for ensuring that code launched by a computer’s UEFI firmware is trusted. It is designed to protect a system against malicious code being loaded and executed early in the boot process before the operating system has been loaded.

  • Measured boot. With a discrete or firmware, TPM Measured Boot is a method where each of the software layers in the boot sequence of the device, measures the next layer in the execution order and extends the value in a designated TPM PCR. Measured boot further validates the boot process beyond Secure Boot.

  • Dual banked firmware updates with rollback and bricking protection provides protection to the firmware update mechanism and shield the device against bricking as well as rollback attacks.

Requirements and specifications

Trusted Substrate interfaces rely on a combination of existing standards:

  • SystemReady compliance

  • SystemReady BBSR compliance (optional in the main case)

  • PSA Firmware Framework A specification compliance (Trust Services)

  • PSCI compliance

  • SCMI compliance

  • ParSec compliance

  • Global Platform TEE compliance

You can find a complete list of the requirements here


The following diagram shows how Trusted Substrate can be seen from upper layers:

Trusted Substrate exists in two flavours that build on SystemReady counterparts: TrustedSubstrate-IR and TrustedSubstrate-ES:

  • TrustedSubstrate-IR implementation is built on Trusted Firmware A, OP-TEE, and U-Boot and uses Device Tree as hardware description. 

  • TrustedSubstrate-ES implementation is built on EDK2, OP-TEE and uses ACPI as hardware description (the main difference with typical data center firmware is the presence of OP-TEE). There are discussions to extend U-Boot to offer full ACPI support in this context.


The primary goal of the project is to upstream all necessary technologies in a number of open-source projects to seed SystemReady compliance. Linaro Edge & Fog computing group hardware as well as Qemu (64 & 32 bits) will be used as reference platforms for the development.

Development of Trusted Substrate is "feature orientated" rather than upstream project orientated. In other words, when a feature is planned, activities in relevant upstream projects is identified and monitored for completion as a whole. Each upstream project has its own roadmap that is not related to SystemReady compliance and is independent from other projects. So if you are evaluating what community to join, the decision criteria is whether your goal is holistic or just focused at an individual project.

NOTE: more details on Trusted Substrate: whys, what, how (note: This presentation was produced before SystemReady was announced. a new version will be authored)

Related Linaro software development  projects

The trusted Substrate project covers a wide range of software components as stated above. To orchestrate engineering activities in manageable pieces, the development is split between the following projects (Trusted Substrate project leadership ensure coherency and completeness across projects):

  • Dependable Boot - ensure SystemReady boot flow conformance across firmware projects (TF-A, OP-TEE, U-Boot, Linux kernel). This project collates work from different teams in Linaro (Kernel Working Group, Security Working Group, LEDGE)

  • - efforts to create a System Device Tree that covers asymmetric computing platforms and to change the lifecycle of Device Tree so that it is provided by firmware to operating systems

  • - while most OP-TEE activities related to SystemReady are guided by Dependable Boot, some long term changes such as Trusted Application lifecycle and distribution scenarios may actually be driven by this project.

  • - the service may be hosted in the SCP, as a TA or even as a VM. When it is distributed as a TA or in the SCP firmware, this service is an integral part of the Trusted Substrate.


Trusted Substrate project deliverables are upstream patches in many upstream projects. The development is driven by the Linaro projects as said above.

Upstream activity can be found in:

  • meta-ts

  • U-Boot, EDK2

  • Trusted-Firmware A, OP-TEE

  • Linux kernel

  • FreeBSD

Currently, TrustedSubstrate-IR for Qemu-BSA 32 bits (U-Boot/DT) and Qemu-BSA 64 bits (EDK2/ACPI and U-Boot/DT) are accessible through the LEDGE Reference Platform downloads.


Linaro is evaluating the opportunity to create SystemReady and Trusted Substrate services such as:

  • Board SystemReady-IR readiness, i.e. making sure the board will pass SystemReady-IR certification

  • include SystemReady-IR CI/CD loops

  • Collaborative maintenance of Trusted Substrate project members defined LTSes (this is very early stages of thinking)

Should you want to have more information or more generally discuss any of the above, please contact us

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Continuous integration


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