SLSA build level 3 compliance on Linux and macOS for Eclipse Temurin


Supply-chain Levels for Software Artifacts, or SLSA, is a framework with individual levels that software producers can work towards to make their software more secure, and consumers can use to make decisions based on the software package’s security posture. The Adoptium project has worked closely with the Eclipse Foundation security team to work towards making the Eclipse Temurin compliant with the SLSA specification’s build requirements.

At the end of 2022 we achieved compliance with level 2 of the SLSA v0.1 specification. In April 2023 SLSA version 1.0 was released and split the specification into multiple “tracks”, of which the build track is the only one currently published. If you’re not familiar with the changes, check out this lightning talk from one of my colleagues. We have been able to build on our work done previously to meet build level 3 for Linux and macOS for Eclipse Temurin’s build and distribution.

What have you done since declaring SLSA level 2?

We have built on top of the work covered in the earlier blog to meet the requirements of SLSA build level 3. The additional requirements were as follows:

Prevent runs from influencing one another, even within the same project

In order to achieve independence between build runs, we perform all of our Linux builds in Docker containers. These containers are instantiated, the build is run and the results saved, and then we shut down the container. This way there can be no influencing from caching or from one run impacting a subsequent one.

We have implemented a comparable system on macOS by using MacStadium’s Orka which allows us to dynamically spin up virtual machines for each build run to give us a comparable level of isolation.

For other operating systems that we build on - Windows, AIX and Solaris - we are not currently set up to do something equivalent which is why we are not claiming SLSA build level 3 for those builds.

Verifying provenance artifacts

We have introduced a build verification step which can take the Software Bill of Materials (SBoM) produced as part of the build output and verify its contents as far as is practical. This will do some checks to ensure that the fields are valid and match expectations about how the product has been built. This job is stored in as which performs SHA and GPG checks as well as running some basic checks on the downloads. It also calls to check the SBoM contents to make sure the dependencies, including compilers, listed in there match expectations. The SBoM contents now also includes the SHA256 checksums of all of the build artifacts in the components section. There is information on programatically verifying the GPG signatures in an earlier blog

In addition to all these checks we also verify after each build that the build code has the features enabled that it should have. This is done using a custom AQA test job called “smoke tests” which use the tests in the build repository in the buildAndPackage directory and test various aspects of the built JDK If these checks fail then these will be trapped early on.

We expect that all of these checks will be enhanced over time, particularly as we add more details into the SBoM.

The current SBoM can be downloaded via the adoptium API. If you are already familiar with the API for downloading JDKs, then replacing jdk with sbom in the URL will let you download the SBoM. For example, this will download the latest GA SBoM for Temurin 21 on Linux/x64:

Note that there is an enhanced version of the SBoM which includes more details on the artifacts that is already in the nightly builds and will be included for the January 2024 GA releases and beyond. We will not (and should not) regenerate the SBoM for older releases.

Prevent secret material used to sign the provenance from being accessible to user-defined build steps

The signing jobs that we use are all contained within our Jenkins CI system. These are independent of the build jobs and run as a subsequent step to avoid the credentials ever being available to the build jobs.

What’s in the future?

At the moment SLSA build level 3 is the highest level available. We will look to keep up to date as updates to the specification are made available. We expect a “level 4” on the build track, and also other tracks to cover source code.

We are also continuing to work on our reproducible builds which gives an extra layer of confidence that any customers of Temurin are able to rebuild from source code in order to independently verify that nothing in our build systems have been tampered with or introduced any unexpected code. Anyone (yes, even you!) can use our fully open-source setup and build scripts to rebuild the Temurin JDK, and we encourage you to give it a try!


Do you have questions or want to discuss this post? Hit us up on the Adoptium Slack workspace!

Stewart X Addison

Posted by Stewart X AddisonAdoptium PMC and steering WG member working for Red Hat