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feat(build): attach a provenance attestation beside the SBOM
An image built with SBOM=1 says what is in it and nothing about how it was built: BUILDX_ARGS set --provenance=false for every build, from when any attestation broke the single-platform stitch. SBOM=1 now also passes --attest type=provenance,mode=min, which BuildKit writes into the same attestation manifest as the SBOM, so the index shape the stitch and the gate read since #4997 is unchanged and a signature over the index covers it. mode=min records the build times, the platform, the frontend and the BuildKit version and leaves out build arguments and secrets, which is what lets it ride every release image. A build without SBOM=1 keeps --provenance=false: the default docker driver cannot attach it, and a PR image turned into an index would buy nothing. Refs #3278 Assisted-by: LLM Signed-off-by: Marian Koreniuk <[email protected]>
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‎docs/release.md‎

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@@ -355,7 +355,7 @@ The script runs the same `cosign verify-blob` before it returns, so a signature
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### SBOM of the container images
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The container images a release pins by digest each carry an SPDX SBOM of the packages in them, which BuildKit attaches at build time as an attestation (`SBOM=1` in `tags.yaml`, scanner and flags in [`hack/common-envs.mk`](../hack/common-envs.mk)). The attestation is an entry of the image's index, so the digest the release pins names both, and promotion copies it with the image. Read it with `docker buildx imagetools inspect <image>@<digest> --format '{{ json .SBOM }}'`, which prints one document per platform. The attestations are not signed. A release cut before `SBOM=1` was set has none, and neither has the Talos installer image, which the imager builds and `skopeo` pushes, nor the third-party images `packages/` vendors by digest.
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The container images a release pins by digest each carry an SPDX SBOM of the packages in them, which BuildKit attaches at build time as an attestation (`SBOM=1` in `tags.yaml`, scanner and flags in [`hack/common-envs.mk`](../hack/common-envs.mk)). The attestation is an entry of the image's index, so the digest the release pins names both, and promotion copies it with the image. Read it with `docker buildx imagetools inspect <image>@<digest> --format '{{ json .SBOM }}'`, which prints one document per platform. The same attestation manifest carries a SLSA provenance statement of the build, in BuildKit's `mode=min` (build times, platform, frontend and BuildKit version, no build arguments and no secrets), which `docker buildx imagetools inspect <image>@<digest> --format '{{ json .Provenance }}'` prints. The attestations are not signed. A release cut before `SBOM=1` was set has none, and neither has the Talos installer image, which the imager builds and `skopeo` pushes, nor the third-party images `packages/` vendors by digest.
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## Nightly builds
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‎hack/common-envs.mk‎

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@@ -66,21 +66,29 @@ PLATFORM ?= $(if $(filter 1,$(LOAD)),,$(DEFAULT_PLATFORMS))
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BUILDX_EXTRA_ARGS ?=
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COZYSTACK_VERSION = $(patsubst v%,%,$(shell git describe --tags --match 'v*'))
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# SBOM=1 attaches an SPDX SBOM to every image as a BuildKit attestation. The
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# pushed ref then names an index of the image and its attestation manifest, not
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# the image itself, which hack/stitch-multiarch.sh and hack/verify-multiarch.sh
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# both handle. Attestations need the docker-container buildx driver. The scanner
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# is pinned by digest like every other build input, where --sbom=true would pull
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# SBOM=1 attaches an SPDX SBOM and a SLSA provenance statement to every image
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# as BuildKit attestations, in one attestation manifest per platform. The
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# pushed ref then names an index of the image and that manifest, not the image
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# itself, which hack/stitch-multiarch.sh and hack/verify-multiarch.sh both
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# handle. Attestations need the docker-container buildx driver. The scanner is
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# pinned by digest like every other build input, where --sbom=true would pull
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# a floating tag. Renovate bumps the version and the digest together, through
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# the manager in .github/renovate.json that reads the SBOM_SCANNER line below.
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#
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# The provenance is mode=min: build times, the build platform, the frontend
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# and BuildKit version, nothing of the build arguments or secrets, so it can
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# ride every release image. Without SBOM=1 provenance stays off: the default
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# docker driver cannot attach it, and it would turn every PR image into an
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# index for nothing that reads it.
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SBOM ?= 0
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SBOM_SCANNER ?= docker.io/docker/buildkit-syft-scanner:1.12.0@sha256:ae4f3b554449e7e25548e7d8ccc029d17357348e30c6e3df01b92bc93654d6a9
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# A variable, because the commas would split the arguments of $(if) below.
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# Variables, because the commas would split the arguments of $(if) below.
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SBOM_ATTEST := --attest type=sbom,generator=$(SBOM_SCANNER)
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PROVENANCE_ATTEST := --attest type=provenance,mode=min
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BUILDX_ARGS := --provenance=false --push=$(PUSH) --load=$(LOAD) \
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BUILDX_ARGS := --push=$(PUSH) --load=$(LOAD) \
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--label org.opencontainers.image.source=https://github.com/cozystack/cozystack \
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$(if $(filter 1,$(SBOM)),$(SBOM_ATTEST)) \
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$(if $(filter 1,$(SBOM)),$(SBOM_ATTEST) $(PROVENANCE_ATTEST),--provenance=false) \
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$(if $(strip $(BUILDER)),--builder=$(BUILDER)) \
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$(if $(strip $(PLATFORM)),--platform=$(PLATFORM)) \
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$(BUILDX_EXTRA_ARGS)

‎hack/common-envs_test.bats‎

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echo "$out" | grep -q -- '--push=0 --load=1'
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}
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@test "SBOM=1 attaches an SPDX attestation from a scanner pinned by digest, and the default builds none" {
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@test "SBOM=1 attaches an SPDX attestation from a scanner pinned by digest and a mode=min provenance, and the default builds none" {
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# An image built with an attestation is an index, not a plain manifest, which
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# the stitch and the gate have to read, so it stays off unless a build asks.
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# --sbom=true would pull the scanner by a floating tag.
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# --sbom=true would pull the scanner by a floating tag. Provenance rides the
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# same attestation manifest; mode=max would write build arguments into it.
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out=$(make -n -C packages/system/cozystack-controller image IMAGE_TAG=pr-1-abc COZYSTACK_VERSION=0 BUILDER=b)
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if echo "$out" | grep -q -- '--attest\|--sbom'; then echo "FAIL: an attestation without SBOM=1"; false; fi
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echo "$out" | grep -q -- '--provenance=false' || { echo "FAIL: provenance not switched off without SBOM=1"; false; }
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out=$(make -n -C packages/system/cozystack-controller image IMAGE_TAG=pr-1-abc COZYSTACK_VERSION=0 BUILDER=b SBOM=1)
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echo "$out" | grep -qE -- '--attest type=sbom,generator=[^ ]+@sha256:[0-9a-f]{64} ' || { echo "FAIL: no digest-pinned scanner"; false; }
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if echo "$out" | grep -q -- '--sbom'; then echo "FAIL: --sbom=true pulls a floating scanner tag"; false; fi
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echo "$out" | grep -q -- '--attest type=provenance,mode=min' || { echo "FAIL: no mode=min provenance beside the SBOM"; false; }
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if echo "$out" | grep -q -- '--provenance=false'; then echo "FAIL: --provenance=false cancels the provenance attestation"; false; fi
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if echo "$out" | grep -qE -- 'provenance,mode=max|--provenance=true'; then echo "FAIL: full provenance would carry build arguments"; false; fi
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# The environment reaches buildx as well, which is how the release workflow sets it.
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out=$(SBOM=1 make -n -C packages/system/cozystack-controller image IMAGE_TAG=pr-1-abc COZYSTACK_VERSION=0 BUILDER=b)
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echo "$out" | grep -q -- '--attest type=sbom,'

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