SBOMs are not being signed

[mthalman]

The build stage of the pipeline generates SBOMs using this logic:

docker-tools/eng/common/templates/jobs/build-images.yml

Lines 128 to 176 in 9791b15

	# Define the task here to load it into the agent so that we can invoke the tool manually
	- task: AzureArtifacts.manifest-generator-task.manifest-generator-task.ManifestGeneratorTask@0
	inputs:
	BuildDropPath: $(Build.ArtifactStagingDirectory)
	displayName: Load Manifest Generator
	condition: and(succeeded(), ne(variables['BuildImages.builtImages'], ''))
	- powershell: |
	$images = "$(BuildImages.builtImages)"
	if (-not $images) { return 0 }
	# There can be leftover versions of the task left on the agent if it's not fresh. So find the latest version.
	$taskDir = $(Get-ChildItem -Recurse -Directory -Filter "ManifestGeneratorTask*" -Path '$(Agent.WorkFolder)')[-1].FullName
	$manifestToolDllPath = $(Get-ChildItem -Recurse -File -Filter "Microsoft.ManifestTool.dll" -Path $taskDir).FullName
	# Check whether the manifest task installed its own version of .NET.
	# To be more robust, we'll handle varying implementations that it's had.
	# First check for a dotnet folder in the task location
	$dotnetDir = $(Get-ChildItem -Recurse -Directory -Filter "dotnet-*" -Path $taskDir).FullName
	if (-not $dotnetDir) {
	# If it's not there, check in the agent tools location
	$dotnetDir = $(Get-ChildItem -Recurse -Directory -Filter "*dotnet-*" -Path "$(Agent.ToolsDirectory)").FullName
	}
	# If the manifest task installed its own version of .NET use that; otherwise it's reusing an existing install of .NET
	# which is executable by default.
	if ($dotnetDir) {
	$dotnetPath = "$dotnetDir/dotnet"
	}
	else {
	$dotnetPath = "dotnet"
	}
	# Call the manifest tool for each image to produce seperate SBOMs
	# Manifest tool docs: https://eng.ms/docs/cloud-ai-platform/devdiv/one-engineering-system-1es/1es-docs/secure-supply-chain/custom-sbom-generation-workflows
	$images -Split ',' | ForEach-Object {
	echo "Generating SBOM for $_";
	$formattedImageName = $_.Replace('$(acr.server)/$(stagingRepoPrefix)', "").Replace('/', '_').Replace(':', '_');
	$sbomChildDir = "$(sbomDirectory)/$formattedImageName";
	New-Item -Type Directory -Path $sbomChildDir > $null;
	& $dotnetPath "$manifestToolDllPath" `
	Generate `
	-BuildDropPath '$(Build.ArtifactStagingDirectory)' `
	-BuildComponentPath '$(Agent.BuildDirectory)' `
	-PackageName '.NET' `
	-PackageVersion '$(Build.BuildNumber)' `
	-ManifestDirPath $sbomChildDir `
	-DockerImagesToScan $_ `
	-Verbosity Information
	}
	displayName: Generate SBOMs

The use of the ManifestGeneratorTask is only used as an "installer" in order to acquire the manifest tool that gets executed in the second step. It's done this way because of the need to have a separate SBOM for each image (see #979). So the SBOM generation occurs in the second step. But the logic for signing the SBOMs actually occurs in the first step via the ManifestGeneratorTask. This means we're not getting the benefit of signing because we're not using the task to generate the SBOMs. And that means none of our SBOMs are signed.

I've logged a related issue for the manifest generator to have another tool that can be used for signing: https://github.com/microsoft/dropvalidator/issues/668

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[mthalman]

[Triage]
One option that could be explored is to include execution of the ManifestGeneratorTask after the explicit step which generates the SBOMs. That may perhaps detect the SBOMs on disk and get them signed. Not sure on that, but if it that works it's a hacky approach to solving this. Ideally, there would be a process that clearly indicates the intent to have the SBOMs signed.

[mthalman]

This work should be incorporated into the work for signing images: dotnet/dotnet-docker#4589.

[lbussell]

The implementation here that currently uses the ManifestGeneratorTask could potentially be simplified by acquiring the sbom-tool directly: https://github.com/microsoft/sbom-tool?tab=readme-ov-file#download-and-installation

EDIT: Even better, we could potentially include the sbom-tool in the ImageBuilder container and call it from there instead of using Pipeline code.