s3cme

Sample Go app repo with test and release pipelines optimized for software supply chain security (S3C).

• Repo Usage
• Provenance Verification
  • Manual
  • In Cluster

What's in the included workflow pipelines:

• on-push - PR qualification
  • Static code vulnerability scan using trivy
  • Repo security alerts based on sarif reports CodeQL scans
• on-tag Release (container image build)
  • Image build/push using ko (includes SBOM generation)
  • Image vulnerability scan using trivy with max severity checks parameter
  • Image signing and attestation using cosign
  • SLSA provenance generation using slsa-framework/slsa-github-generator
  • SLSA provenance verification using both, slsa-framework/slsa-verifier, CUE policy using cosign
• on-schedule - Repo hygiene
  • Semantic code analysis using CodeQL (every 4 hours)

Repo Usage

Use this template to create a new repo (click the green button and follow the wizard)

When done, clone your new repo locally, and navigate into it

git clone git@github.com:$GIT_HUB_USERNAME/$REPO_NAME.git
cd $REPO_NAME

Initialize your new repo. This will update all the references to your newly clone GitHub repository.

tools/init-repo

When completed, commit and push the updates to your repository:

git add --all
git commit -m 'repo init'
git push --all

The above push will trigger the on-push flow. You can navigate to the /actions in your repo to see the status of that pipeline.

Trigger release pipeline

The canonical version of the entire repo is stored in .version file. Feel free to edit it (by default: v0.0.1). When done, trigger the release pipeline:

If you did edit the version, make sure to commit and push that change to the repo first. You can also use make tag to automate the entire process.

export VERSION=$(cat .version)
git tag -s -m "initial release" $VERSION
git push origin $VERSION

Monitor the pipeline

Navigate to /actions in your repo to see the status of that release pipeline. Wait until all steps (aka jobs) have completed (green).

If any steps fail, click on them to see the cause. Fix it, commit/push changes to the repo, and tag a new release to re-trigger the pipeline again.

Review produced image

When successfully completed, that pipeline will create an image. Navigate to the registry to confirm the image was created.

This link will take you to the original template registry. Replace username and repo to navigate to yours.

https://github.com/mchmarny/s3cme/pkgs/container/s3cme

The image is the line item tagged with version (e.g. latest). The other three OCI artifacts named with the image digest in the registry are:

• .sig - cosign signature
• .att - SLSA attestations
• .sbom - SBOM (SPDX v2.3)

You can now take the image digest and query sigstore transparency service (Rekor). Easiest way to do that is to use the Chainguard's rekor-search-ui. Here is the entry for s3cme v0.6.35.

Provenance Verification

Whenever you tag a release in the repo and an image is push to the registry, that image has an "attached" attestation in a form of SLSA provenance (v0.2). This allows you to trace that image all the way to its source in the repo (including the GitHub Actions that were used to generate it). That ability for verifiable traceability is called provenance.

Manual

To verify the SLSA build provenance of an image that was generated by the on-tag pipeline manually cosign:

cosign verify-attestation \
   --type slsaprovenance \
   --certificate-identity-regexp "^https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@refs/tags/v[0-9]+.[0-9]+.[0-9]+$" \
   --certificate-oidc-issuer https://token.actions.githubusercontent.com \
   --policy policy/provenance.cue \
   $digest

The terminal output will include the checks that were executed as part of the validation, as well as information about the subject (URI of the tag ref that triggered that workflow), with its SHA, name, and Ref.

The following checks were performed on each of these signatures:
  - The cosign claims were validated
  - Existence of the claims in the transparency log was verified offline
  - The code-signing certificate was verified using trusted certificate authority certificates
Certificate subject: https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@refs/tags/v1.5.0
Certificate issuer URL: https://token.actions.githubusercontent.com
GitHub Workflow Trigger: push
GitHub Workflow SHA: 5ed1e3b75214316fd5cd09e77b88f41c01ea85ec
GitHub Workflow Name: on_tag
GitHub Workflow Repository: mchmarny/s3cme
GitHub Workflow Ref: refs/tags/v0.6.35

The output will also include JSON, which looks something like this (payload abbreviated):

{
   "payloadType": "application/vnd.in-toto+json",
   "payload": "eyJfdHl...V19fQ==",
   "signatures": [
      {
         "sig": "MEUCIQCl+9dSv9f9wqHTF9D6L1bizNJbrZwYz0oDtjQ1wiqmLwIgE1T1LpwVd5+lOnalkYzNftTup//6H9i6wKDoCNNhpeo="
      }
   ]
}

The payload field (abbreviated) is the base64 encoded in-toto statement containing the predicate containing the GitHub Actions provenance:

... | jq -r .payload | base64 -d | jq -r .

Returns:

{
    "_type": "https://in-toto.io/Statement/v0.1",
    "predicateType": "https://slsa.dev/provenance/v0.2",
    "subject": [
        {
            "name": "ghcr.io/mchmarny/s3cme",
            "digest": {
                "sha256": "c85cdbb4cff81cd12f12af9cc7da4929f1b653a55896501e18755674739403fa"
            }
        }
    ],
    "predicate": {...}
}

In Cluster

You can also verify the provenance of an image in your Kubernetes cluster.

This assumes you already configured the sigstore admission controller in your Kubernetes cluster. If not, you can use the provided tools/gke-cluster script to create a cluster and configure sigstore policy-controller.

First, review the policy/cluster.yaml file, and make sure the glob pattern matches your Artifact Registry (** will match any character). You can make this as specific as you want (e.g. any image in the project in specific region)

images:
- glob: ghcr.io/mchmarny/**

Next, check the subject portion of the issuer identity (in this case, the SLSA generator workflow for containers, with the repo tag)

identities:
- issuer: https://token.actions.githubusercontent.com
  subjectRegExp: "^https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@refs/tags/v[0-9]+.[0-9]+.[0-9]+$"

Finally, the policy data that checks for predicateType on the image should include the content of the same policy (policy/provenance.cue) we've used during the SLSA verification using image release and in the above manual verification process.

policy:
   type: cue
   data: |
     predicateType: "https://slsa.dev/provenance/v0.2"
     ...

Make sure the content is indented correctly

When finished, apply the policy into the cluster:

kubectl apply -f policy/slsa.yaml

To verify SLSA provenance on any namespace in your cluster, add a sigstore inclusion label to that namespace (e.g. demo):

kubectl label ns demo policy.sigstore.dev/include=true

Now, you should see an error when deploying images that don't have SLSA attestation created by your release pipeline:

kubectl run test --image=nginxdemos/hello -n demo

Will result in:

admission webhook "policy.sigstore.dev" denied the request: validation failed: no matching policies: spec.containers[0].image
index.docker.io/nginxdemos/hello@sha256:46bd594006f4bacc8a6c1cc2941ef842caf2358bc258619f7bea1558bc461b38

That policy failed because the image URI doesn't match the images glob we've specified (glob: ghcr.io/mchmarny/**). How about if we try to deploy image that does, but does not have SLSA attestation:

kubectl run test -n demo --image ghcr.io/mchmarny/s3cme-no-slsa@sha256:0d8b8a9e3635545476b880612d5a058616d7ac378b79b67ad412e9a9c11e7e45

Now the failure is on the SLSA policy due to lack of verifiable attestations:

admission webhook "policy.sigstore.dev" denied the request: validation failed: failed policy: slsa-attestation-image-policy: spec.containers[0].image
ghcr.io/mchmarny/s3cme@sha256:c85cdbb4cff81cd12f12af9cc7da4929f1b653a55896501e18755674739403fa attestation keyless validation failed for authority authority-0 for ghcr.io/mchmarny/s3cme@sha256:0d8b8a9e3635545476b880612d5a058616d7ac378b79b67ad412e9a9c11e7e45: no matching attestations:

Finally deploy image form the trusted registry and with SLSA attestation:

kubectl run test -n demo --image ghcr.io/mchmarny/s3cme@sha256:c85cdbb4cff81cd12f12af9cc7da4929f1b653a55896501e18755674739403fa

Now, the response is simple:

pod/test created

This demonstrates how the policy-controller admission controller enforces SLSA provenance policy in your cluster based on verifiable supply-chain metadata from cosign.

Disclaimer

This is my personal project and it does not represent my employer. While I do my best to ensure that everything works, I take no responsibility for issues caused by this code.