policy: builder-image v1 with attested inputs, SBOMs, and VEX

.github/scripts/verify_builder_policy.py

@@ -136,6 +136,95 @@ def check_image_attested(ctx, params):
     return errs
 
 
+def _digest_ok(ctx, a, errs):
+    d = ctx.digests.get(a)
+    if isinstance(d, str) and DIGEST_RE.match(d):
+        return d
+    errs.append(f"{a}: image digest missing or malformed: {d!r}")
+    return None
+
+
+def _attested_predicates(ctx, a, d, params, ptype, source_ref, errs):
+    """gh attestation verify the image digest for one predicate type; return the list of
+    verified predicates (empty list if none), or None after recording an error."""
+    rc, out = ctx.run([
+        "gh", "attestation", "verify", f"oci://{params['image']}@{d}",
+        "--repo", params["repo"],
+        "--signer-workflow", params["signer_workflow"],
+        "--source-ref", source_ref,
+        "--source-digest", ctx.tag_sha,
+        "--predicate-type", ptype,
+        "--format", "json",
+    ])
+    if rc != 0:
+        errs.append(f"{a}: gh attestation verify failed for {ptype} on {d}")
+        return None
+    try:
+        results = json.loads(out)
+    except ValueError:
+        errs.append(f"{a}: gh attestation verify output is not JSON ({ptype})")
+        return None
+    preds = []
+    for r in results if isinstance(results, list) else []:
+        stmt = ((r or {}).get("verificationResult") or {}).get("statement") or {}
+        preds.append(stmt.get("predicate"))
+    if not preds:
+        errs.append(f"{a}: no {ptype} attestation returned for {d}")
+        return None
+    return preds
+
+
+def _predicate_equals(ctx, a, d, params, ptype, source_ref, doc, label, errs):
+    if not isinstance(doc, dict):
+        errs.append(f"{a}: released {label} missing")
+        return
+    preds = _attested_predicates(ctx, a, d, params, ptype, source_ref, errs)
+    if preds is not None and doc not in preds:
+        errs.append(f"{a}: released {label} differs from the attested predicate on {d}")
+
+
+def check_inputs_attested(ctx, params):
+    """builder-inputs.<arch>.json is the predicate of a verified attestation on that arch's
+    image digest (named workflow, main, tagged commit, named predicate type)."""
+    errs = []
+    for a in ARCHES:
+        d = _digest_ok(ctx, a, errs)
+        if d:
+            _predicate_equals(ctx, a, d, params, params["predicate_type"], params["source_ref"],
+                              ctx.inputs.get(a), "builder-inputs.json", errs)
+    return errs
+
+
+def check_sbom_attested(ctx, params):
+    """The released CycloneDX and SPDX SBOMs are the predicates of verified attestations on the
+    image digest, made by the release workflow from the release tag."""
+    errs = []
+    sref = params["source_ref_template"].format(tag=ctx.tag)
+    for a in ARCHES:
+        d = _digest_ok(ctx, a, errs)
+        if not d:
+            continue
+        cdx, spdx = ctx.sboms.get(a), ctx.spdx.get(a)
+        _predicate_equals(ctx, a, d, params, params["cyclonedx_predicate_type"], sref, cdx, "CycloneDX SBOM", errs)
+        ver = str((spdx or {}).get("spdxVersion", "")).partition("-")[2]
+        if not ver:
+            errs.append(f"{a}: SPDX SBOM missing or has no spdxVersion")
+            continue
+        _predicate_equals(ctx, a, d, params, params["spdx_predicate_type_prefix"] + ver, sref, spdx, "SPDX SBOM", errs)
+    return errs
+
+
+def check_vex_attested(ctx, params):
+    """The released OpenVEX file is the predicate of a verified attestation on each image digest."""
+    errs = []
+    sref = params["source_ref_template"].format(tag=ctx.tag)
+    for a in ARCHES:
+        d = _digest_ok(ctx, a, errs)
+        if d:
+            _predicate_equals(ctx, a, d, params, params["predicate_type"], sref, ctx.vex, "builder.openvex.json", errs)
+    return errs
+
+
 def check_gate_script_hash(ctx, params):
     import hashlib
     want = hashlib.sha256(ctx.git_show(params["script_path"])).hexdigest()

.github/workflows/build-environment-image.yml

@@ -14,6 +14,7 @@ on:
 env:
   IMAGE: ghcr.io/${{ github.repository_owner }}/python-wheels-builder-alpine
   CONTEXT: environments/alpine-3.24-musl
+  INPUTS_PREDICATE_TYPE: https://github.com/patrickryankenneth/python-wheels-builder/predicate/builder-inputs/v1
 
 # No default permissions; each job asks for exactly what it needs.
 permissions: {}
@@ -106,7 +107,7 @@ jobs:
           echo "\`$IMAGE@$DIGEST\`" >> "$GITHUB_STEP_SUMMARY"
 
       - name: Attest build provenance
-        uses: actions/attest-build-provenance@96278af6caaf10aea03fd8d33a09a777ca52d62f # v3.2.0
+        uses: actions/attest@1e69f48acb82d1966a394da916b4c1698aa569d6 # v4.2.2
         with:
           subject-name: ghcr.io/${{ github.repository_owner }}/python-wheels-builder-alpine
           subject-digest: ${{ steps.push.outputs.digest }}
@@ -176,6 +177,29 @@ jobs:
               builder_image:$builder_image, source_commit:$commit}' > "builder-inputs.$ARCH.json"
           cat "builder-inputs.$ARCH.json"
 
+      - name: Attest builder inputs
+        uses: actions/attest@1e69f48acb82d1966a394da916b4c1698aa569d6 # v4.2.2
+        with:
+          subject-name: ghcr.io/${{ github.repository_owner }}/python-wheels-builder-alpine
+          subject-digest: ${{ steps.push.outputs.digest }}
+          predicate-type: ${{ env.INPUTS_PREDICATE_TYPE }}
+          predicate-path: builder-inputs.${{ matrix.arch }}.json
+          push-to-registry: true
+
+      - name: Verify the builder-inputs attestation we just made
+        env:
+          GH_TOKEN: ${{ github.token }}
+          DIGEST: ${{ steps.push.outputs.digest }}
+          ARCH: ${{ matrix.arch }}
+        run: |
+          set -euo pipefail
+          gh attestation verify "oci://$IMAGE@$DIGEST" \
+            --repo "${{ github.repository }}" \
+            --signer-workflow "${{ github.repository }}/.github/workflows/build-environment-image.yml" \
+            --predicate-type "$INPUTS_PREDICATE_TYPE" --format json \
+            | jq -e --slurpfile want "builder-inputs.$ARCH.json" \
+                'any(.[]; .verificationResult.statement.predicate == $want[0])' > /dev/null
+
       - name: Upload digest and inputs
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with: