Firmware Over The Air

The firmware update is critical since its alteration back to compromise the entire system. It is therefore necessary to take appropriate protective measures.

AGL includes the meta-updater Yocto layer that enables OTA software updates via Uptane, an automotive-specific extension to The Update Framework. Uptane and TUF are open standards that define a secure protocol for delivering and verifying updates even when the servers and network–internet and car-internal–aren’t fully trusted.

meta-updater includes the application aktualizr, developed Advanced Telematic Systems (now part of HERE Technologies) that enables OTA for an ECU. aktualizr combined with Uptane is suitable for updating the firmware, software, and other packages on even functionally critical ECUs. aktualizr can be enabled with the free, open souce backend ota-community-edition.

This FOTA update mechanism can be enabled through the agl-sota feature.

Building

To build an AGL image that uses aktualizr, the following can be used.

source meta-agl/scripts/aglsetup.sh -m <machine> agl-sota <other-features...>

During the build, meta-updater will use credentials downloaded from ota-community-edition to sign metadata verifying the build as authentic. These signatures are part of the Uptane framework and are used to verify FOTA updates.

Atomic Upgrades with Rollbacks

aktualizr’s primary method of updating firmware is to use libostree with binary diffs. The binary diffs use the least amout of bandwidth, and by it’s nature libostree stores current and previous firmware versions on disk or in flash memory to allow for rollbacks.

libostree is a content addressable object store much like git. Versions are specified via SHA2-256. These hashes are signed in the Uptane metadata and are robust against cryptographic compromise.