Linaro Engineering Highlights: May 2020

21 mins read

Linaro AI Project: uTVM

By Tom Gall, Director, AI/ML Project Lead

AI icon

TVM is an AI compiler for inferencing which can create highly optimized binaries for deploying on ARM systems. Micro TVM or uTVM is an effort to leverage the advanced technology in the compiler infrastructure as applied to microcontroller devices.

From the Members meeting in January you might remember the exercise to determine what activities would bring value to Linaro members involving AI on microcontrollers. The recommendation delivered to the LITE-SC was to approve a uTVM project as part of the AI efforts within Linaro. The LITE-SC vote is in progress as this is being written.

If any individual member would like a briefing we are happy to do so.

A product level specification, internal to Members and Linaro only, has been created which documents the various modifications / goals that need to be completed in order to evolve uTVM from its current PoC/Alpha state to a mature piece of software which can be utilized within Member products. The creation of this document is a group effort by those engaged in the project. The document will serve as our roadmap to success

Engineering related to the project has already begun:

Arm Ethos-N integration RFC

First microTVM testcase (Merged)

The project is open to club/core Members to join. If a Member is not a club or core Member or part of the LITE-SC, they may also join by either joining LITE or by becoming a project member.

Email for details or questions.

Firmware Framework for Arm (FFA) Specification (1.0 EAC release)

By Mike Holmes, Director, Foundational Technologies

Core Engineering icon

Arm and Linaro have been collaborating on prototypes with changes in the OP-TEE kernel driver, OP-TEE OS and Trusted Firmware based on the different versions of the FFA (formerly SPCI) specification. Having the OP-TEE regression suite xtest pass has improved confidence in the different versions of the specifications. Later versions of the prototypes have also included a secure world (S-EL2) hypervisor based on Hafnium. Linaro created the first prototype and after that it has been a shared effort.

KissCache: A New Caching Server

By Ryan Arnold, Director, System Technologies

LKFT icon

KissCache, the “simple and stupid caching server”, is a newly released open source project from Linaro that is now used in production by the Linux Kernel Functional Test (LKFT) project. KissCache is used to cache and serve binary artifacts to Linaro’s LKFT LAVA instance. These artifacts are held in Amazon S3. Using Kisscache both saves Linaro money by caching artifacts in the Linaro lab (reducing bandwidth usages from S3) as well as increases job execution time because artifacts are served much more quickly, and therefore systems are provisioned more quickly.

Unlike classical proxies like Squid that transparently intercept traffic, in order to use KissCache one must explicitly prefix the requested URL by the URL of the local KissCache instance. KissCache will download the requested resource in the background while streaming it to the client. Kisscache’s primary use case is for downloading and caching https (secure) content. It preserves the chain of trust, whereas Squid really only works properly with non-secure content.

If many clients are requesting the same resource, KissCache will download it only once and stream the content to every client. In the last month, Linaro’s KissCache deployment handled more than 160k requests, serving 32TB of data while only downloading 1TB from outside of the Linaro lab. This has a real cost savings of over $2000 per month.

Tuxpub - The Serverless Cloud-Based Artifact Server

By Ryan Arnold, Director, System Technologies

LKFT icon

At Linaro, we have often hosted artifacts from Amazon S3 using a custom tool known as Linaro License Protection (LLP). LLP started life serving files from local disk storage, then later moved to use Amazon S3. Technically LLP provides an S3 browsing interface. However it was never designed to run under a serverless architecture. This coupled with other necessary Linaro/License features (such as authentication) means that LLP doesn’t fit a “simple serverless” model.

Linaro is presently working on a SaaS offering called TuxBuild (and companion service called TuxBoot). These technologies are implemented using the new serverless model and have a need to provide artifacts from cloud storage using a lightweight application that provides a file browser as a web-based user front end.

The original implementation of Tuxpub used Javascript, but we quickly realised it wasn’t scalable, it wasn’t conformant with what web tools expect, and it lacked features which our users were demanding (such as the ability to pull the file contents in JSON) for browsing programmatically. After searching for existing solutions we discovered that there were no available light-weight tools to solve our problems!

We built a wishlist of the following features and requirements that we felt a proper file server would honour and set about building tuxpub:

  • Serverless methodology for easy deployment and management
  • Ability to block the index page so people cannot browse other folders
  • Allow users to access a JSON output of the page for easy downloading

The following is a sample file browser front-end being served by tuxpub for the TuxBuild project:

sample file
How easy is it to deploy and manage?

Linaro can deploy our tuxpub instances with two lines of code and a config file! This procedure is documented in the TuxPub readme. To bring up a TuxPub instance a developer only needs to create an application shim with the following zappa code:

    "dev": {
        "app_function": "",
        "aws_region": "us-east-1",
        "project_name": "lkft-tuxpub",
        "runtime": "python3.7",
        "s3_bucket": "zappa-tuxpub",
        "environment_variables": {
          "S3_BUCKET": "",
          "S3_REGION": "us-east-1",
          "ROOT_INDEX_LISTING": "True",

With these files a developer needs to build up a pipenv file with “pipenv install –deploy”, and then deploy it into AWS Lambda with “zappa deploy dev”.

One can even run the application locally with “ S3_REGION=us-east-1 ROOT_INDEX_LISTING=True FLASK_APP=tuxpub flask run”.

What are the limitations?

Since tuxpub uses the AWS API, there are limitations set by the cloud provider. An index page with more than 1000 objects hits an API limit and generates a nasty error page. Because of this, we intend to implement ‘paging’ support. Tuxpub does not presently support user authentication and has no immediate plans to add it.

Can others use and contribute to tuxpub?

Linaro has made tuxpub available as open source software under the MIT license. This means that it’s free to deploy and modify. We’re very welcoming of pull requests! You can find the code here.

What is the future of tuxpub?

Linaro’s objective is to keep this application simple! We are being selective and do not want to add too many features that would bloat the application. Desirable features additions (most notably paging support) are being collected in tuxpub gitlab issues and addressed over time.

RDK and i.MX8

By Tom Gall, Director, Linaro Consumer Group

Multimedia icon

The RDK 3.0 port to iMX8M reached a new milestone where now contains detailed information on how to build and also run the RDK 3.0 on MCIMX8M-EVK NXP board. In addition, work has already progressed rapidly on the migration to Yocto Dunfell LTS release which is documented here. The i.MX8M SoC has become the Linaro reference SoC for secure video path developments for the major ecosystems Linaro is involved with for secure video (RDK, Linux & AOSP) where a fully secure video pipeline is required.

Features showcased in the i.MX8M RDK port include the App Manager framework. This is a cross platform application engine that allows STB applications to be written in JavaScript but access the native rendering functionality of the underlying platform. The other main showcased feature is the Thunder application framework (aka, WPEFramework) and the integration of DRM technologies from Linaro into the wpewebkit browser to facilitate the playback of protected content. Linaro has upstreamed many patches to meta-wpe, Thunder, ThunderNanoServices, WPEWebKit and the ocdm-* plugins as part of this project. It has been an example of the productive collaboration that can happen inside Linaro between Comcast, NXP and Linaro engineers.

Raspberry Pi Libcamera Initiative

By Tom Gall, Director, Linaro Consumer Group

Raspberry Pi Libcamera icon

The libcamera project reached a big new milestone with the joint announcement from RPi foundation and libcamera projects on the first fully open source camera stack including 3A (auto exposure, auto gain control, auto white balance) algorithms. This is the first SoC in libcamera to become fully enabled in terms of 3A, and as far as we are aware the first time 3A algorithms have been fully open sourced in any meaningful way. More about the announcement can be found here.

LEDGE Reference Platform Stage 3 available

By Francois Ozog, Director, Linaro Edge and Fog Computing

Ledge icon

The LEDGE Reference Platform builds on the Generic Kernel Image concept pioneered by Google for Android. The ultimate goal is that Linaro members and Linux distribution providers (commercial or not) can deliver a single binary image that can be booted on any Embedded Base Boot Requirement (EBBR) compliant platform. The LEDGE Reference Platform builds on the efforts of the Dependable Boot project which focuses on building an EBBR compliant firmware environment.

In more technical terms, LEDGE Reference Platform is a lightweight highly secure and robust container runtime environment that has dependable boot and update capabilities. It comes with a full set of security policies with SELinux, Integrity Measurement Architecture enabled and other technologies that can be further adapted to specific markets.

There are actually three images built: 64 bits, 32 bits, 32 bits with LPAE enabled. With Stage 3, the LEDGE Reference Platform can be booted with UEFI SecureBoot (U-Boot or EDK2) and it was verified that:

  • A single 64 bits image can be booted on QEMU, NXP LS21060ARDB, Socionext Synquacer( and expect to achieve this with kernel 5.8 on TI AM65XX)
  • A single 32 bits image can be booted on TI AM572x and BEAGLEBOARD-X15, ST STM32MP157C-DK2 and QEMU

Reference Platform stage 4 has started. It will come with an integrated standard and generalized firmware update features based on UEFI update capsules. We shall build on system-d defined boot-blessing capabilities to provide a robust boot orchestration scheme that will leverage hardware anti-bricking and anti-rollback features.

Linaro Tech Days Sessions from LITE team

By Vicky Janicki, Linaro IoT and Embedded Group

Lite icon

The Linaro Embedded and IoT Team ran a 3 session series in April and May under the Linaro Tech Days Banner. Vincent Wan (TI) reviewed “Power Management On Zephyr” to start. For the second session, Paul Sokolovskyy (Linaro) presented “Update on LAVA Testing for Bare Metal Systems” which charted LITE’s effort to enhance LAVA to work more effectively with MCU’s. Manivannan Sadhasivam, a kernel engineer from Linaro Developer Services presented “LoRa Meets Zephyr” which included a brief history of LoRa, what is currently working and what remains. All three sessions can be found on the Linaro Tech Days Resource Page.

Trusted-Firmware-M Integration with Zephyr 2.3

By Kevin Townsend, Senior Engineer, Linaro IoT and Embedded Group

Lite icon

The upcoming 2.3 release of Zephyr now features out of the box support for Trusted-Firmware-M, including hardware emulation via QEMU, meaning you don’t require physical access to a supported development board.

Zephyr is configured to run in the non-secure processing environment, and TF-M is used in the secure processing environment, with communication between the two environments happening over TF-M’s IPC mechanism. Both secure and non-secure images are signed, and validated by the secure BL2 bootloader at startup. Zephyr applications can make direct use of the PSA APIs for Cryptography, Initial Attestation, etc., and the IPC mechanism will be handled transparently from an application point of view.

General Requirements

This post details some of the steps required to test TF-M integration in Zephyr using QEMU, with only minor changes required to run the samples on actual hardware.

NOTE : Zephyr currently supports TF-M integration with the MPS2 AN521 and Musca B1 board targets, with LPCXpresso55S69 support planned in the near future now that LPC55S69 support is available upstream in TF-M. The AN521 build target has been setup in Zephyr to optionally work with QEMU.

Zephyr 2.3 RC1 was used writing this, but 2.3 may be finalised by the time you read this. The instructions found here should remain consistent with anything from 2.3 RC1 and higher.

At present, the TF-M integration has been tested on the following platforms, and will not work on Windows out of the box:

  • Ubuntu 18.04 using Zephyr SDK 0.11.3
  • macOS Mojave using QEMU 4.2.0 with gcc-arm-none-eabi-7-2018-q2-update
Zephyr Setup

Follow Zephyr’s Getting Started Guide available here.

TF-M Setup

TF-M has a few additional requirements to enable building the secure-side firmware image. The following Python packages must be available on your system, since they are used by TF-M when signing binary images for secure bootloader verification at startup:

$ pip3 install --user cryptography pyasn1 pyyaml cbor>=1.0.0

Additionally, the srec_cat utility is required when merging signed application images at the end of the build process. This can be installed via the srecord package available on both Linux(-y) distributions and OS X via some variation of:

$ sudo apt-get install srecord

Or in the case of OS X:

$ brew install srecord
QEMU Setup

If you are using the Zephyr SDK on Linux, QEMU 4.2.0 is already included in the SDK and no further action is required.

If you are using OS X, however, you will also need to install QEMU and make it available on your system path. QEMU 4.0.0 included support for the AN521 target, but we recommend using QEMU 4.2.0 or higher, which is the release used in the Zephyr SDK and during the TF-M/Zephyr integration work. This is generally as easy as running:

$ brew install qemu

You can test the installation and path access with the following command:

$ qemu-system-arm --version
QEMU emulator version 4.2.0
Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developers
Building a TF-M application

At this point we can build a test application in Zephyr via the following command sequence:

$ source zephyr/
$ west build -p -b mps2_an521_nonsecure zephyr/samples/tfm_integration/psa_level_1/ -t run

This will cause TF-M to be built in the background, and the S image (from TF-M- and NS image (from Zephyr) will both be signed with a signature that the BL2 secure bootloader will accept, and an optional binary for QEMU will be generated in addition to the standard AN521 binary images. The -t run flag will cause QEMU to execute the specially prepared binary once the build process is complete, and you should see some variation of the following output:

[INF] Starting bootloader
[INF] Image 0: version=0.0.0+1, magic= good, image_ok=0x3
[INF] Image 1: No valid image
[INF] Booting image from the primary slot
[INF] Bootloader chainload address offset: 0x80000
[INF] Jumping to the first image slot
[Sec Thread] Secure image initializing!
TF-M isolation level is: 1
Booting TFM v1.0
*** Booting Zephyr OS build v2.3.0-rc1  ***
[00:00:00.003,000] <inf> app: app_cfg: Creating new config file with UID 0x155cfda7a
[00:00:03.516,000] <inf> app: att: System IAT size is: 453 bytes.
[00:00:03.516,000] <inf> app: att: Requesting IAT with 64 byte challenge.
[00:00:06.922,000] <inf> app: att: IAT data received: 453 bytes.
          0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
00000000 D2 84 43 A1 01 26 A0 59 01 79 AA 3A 00 01 24 FF ..C..&.Y.y.:..$.
00000010 58 40 00 11 22 33 44 55 66 77 88 99 AA BB CC DD X@.."3DUfw......
00000020 EE FF 00 11 22 33 44 55 66 77 88 99 AA BB CC DD ...."3DUfw......
00000030 EE FF 00 11 22 33 44 55 66 77 88 99 AA BB CC DD ...."3DUfw......
00000040 EE FF 00 11 22 33 44 55 66 77 88 99 AA BB CC DD ...."3DUfw......
00000050 EE FF 3A 00 01 24 FB 58 20 A0 A1 A2 A3 A4 A5 A6 ..:..$.X .......
00000060 A7 A8 A9 AA AB AC AD AE AF B0 B1 B2 B3 B4 B5 B6 ................
00000070 B7 B8 B9 BA BB BC BD BE BF 3A 00 01 25 00 58 21 .........:..%.X!
00000080 01 FA 58 75 5F 65 86 27 CE 54 60 F2 9B 75 29 67 ..Xu_e.'.T`..u)g
00000090 13 24 8C AE 7A D9 E2 98 4B 90 28 0E FC BC B5 02 .$..z...K.(.....
000000A0 48 3A 00 01 24 FA 58 20 AA AA AA AA AA AA AA AA H:..$.X ........
000000B0 BB BB BB BB BB BB BB BB CC CC CC CC CC CC CC CC ................
000000C0 DD DD DD DD DD DD DD DD 3A 00 01 24 F8 20 3A 00 ........:..$. :.
000000D0 01 24 F9 19 30 00 3A 00 01 24 FD 81 A5 01 63 53 .$..0.:..$....cS
000000E0 50 45 04 65 30 2E 30 2E 30 05 58 20 BF E6 D8 6F PE.e0.0.0.X ...o
000000F0 88 26 F4 FF 97 FB 96 C4 E6 FB C4 99 3E 46 19 FC .&..........>F..
00000100 56 5D A2 6A DF 34 C3 29 48 9A DC 38 06 66 53 48 V].j.4.)H..8.fSH
00000110 41 32 35 36 02 58 20 C9 16 54 69 9C 13 DA 27 43 A256.X ..Ti...'C
00000120 5C D1 28 80 3D B6 B3 50 0A BC 70 87 39 97 BF 5E \.(.=..P..p.9..^
00000130 9A 58 53 7E 24 4D F1 3A 00 01 25 01 77 77 77 77 .XS~$M.:..%.wwww
00000140 2E 74 72 75 73 74 65 64 66 69 72 6D 77 61 72 65 .trustedfirmware
00000150 2E 6F 72 67 3A 00 01 24 F7 71 50 53 41 5F 49 4F .org:..$.qPSA_IO
00000160 54 5F 50 52 4F 46 49 4C 45 5F 31 3A 00 01 24 FC T_PROFILE_1:..$.
00000170 72 30 36 30 34 35 36 35 32 37 32 38 32 39 31 30 r060456527282910
00000180 30 31 30 58 40 51 33 D9 87 96 A9 91 55 18 9E BF 010X@Q3.....U...
00000190 14 7A E1 76 F5 0F A6 3C 7B F2 3A 1B 59 24 5B 2E .z.v...<{.:.Y$[.
000001A0 67 A8 F8 AB 12 6E 7F 97 FB 28 35 97 89 A5 56 61 g....n...(5...Va
000001B0 8F 00 4E A7 D1 37 5B E5 C1 6A 30 3C F2 00 97 17 ..N..7[..j0<....
000001C0 04 0F 91 74 DA                              	...t.
[00:00:06.964,000] <inf> app: Persisting SECP256R1 key as #1
[00:00:09.402,000] <inf> app: Retrieving public key for key #1
          0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
00000000 04 47 EA AE D9 D6 6D 2E 1D 65 05 F5 04 FE CC 21 .G....m..e.....!
00000010 99 BE 5E 5A 56 6B 4F 1E 0C 43 E2 5B CE 1B 7D 06 ..^ZVkO..C.[..}.
00000020 D7 B3 71 E2 0A 3C 47 ED 84 9F 65 0E DB F9 3D D2 ..q..<G...e...=.
00000030 07 BB 81 A6 73 E6 3B 16 95 19 AC 01 02 CB 1C F5 ....s.;.........
00000040 35                         	                 5
[00:00:11.833,000] <inf> app: Calculating SHA-256 hash of value
          0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
00000000 50 6C 65 61 73 65 20 68 61 73 68 20 61 6E 64 20 Please hash and
00000010 73 69 67 6E 20 74 68 69 73 20 6D 65 73 73 61 67 sign this messag
00000020 65 2E                                       	e.
          0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
00000000 9D 08 E3 E6 DB 1C 12 39 C0 9B 9A 83 84 83 72 7A .......9......rz
00000010 EA 96 9E 1D 13 72 1E 4D 35 75 CC D4 C8 01 41 9C .....r.M5u....A.
[00:00:11.853,000] <inf> app: Signing SHA-256 hash
          0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
00000000 81 FC CE C2 02 96 79 E0 60 A8 0C 53 22 58 F3 17 ......y.`..S"X..
00000010 7A AC 46 60 7E 30 7F 60 03 53 1C 43 CA 31 97 B8 z.F`~0.`.S.C.1..
00000020 47 47 56 E9 19 45 F9 E2 DC 38 68 8D F1 A7 C7 48 GGV..E...8h....H
00000030 96 26 F6 0C 0F 94 D8 E3 9E 66 82 76 A6 BC B4 FC .&.......f.v....
[00:00:15.201,000] <inf> app: Verifying signature for SHA-256 hash
[00:00:20.987,000] <inf> app: Signature verified.
[00:00:23.441,000] <inf> app: Destroyed persistent key #1

Extending the TF-M Sample Applications

The sample application above can easily be extended, or a new application can be started based on one of the samples available here.

Consult the PSA API documentation or TF-M source code, linked below, for details on how to extend the samples:

Key References

The following links are useful to further develop custom applications based on Zephyr 2.3+ and TF-M:

  • PSA API Documentation: Click here
  • TF-M Source Code: Click here.
  • Zephyr’s fork of TF-M for any pull requests or bug reports: Click here.

Community News

By Mike Holmes, Foundational Technologies

Stewardship icon

The Linux Test Project test suite stable release for “May 2020” has been released with notable contributions from Linaro. Viresh Kumar (Kernel Working Group) was featured in the top three for his effort to provide complete coverage of the Syscalls in the LTP suite.

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