c-wcow policy and blockcim tooling - #2870
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Add a small, pure-Go, cross-platform tool that reads the sealed root hash of a block CIM (containerd's layer.vhd or the securitypolicy tooling's *.bcim) directly from its on-disk metadata, without the Windows CIM APIs. The sealed root hash is the value cimfs.GetVerificationInfo returns and what a confidential policy digest compares against, so being able to read it on any platform makes digest mismatches debuggable. The tool also prints the BlockDeviceHeader and PrimaryBlockTable (including each entry's CimName and content hash), which is what surfaced that the embedded CimName contributes to the root digest. - Cluster size is auto-detected from the header ((1<<Exponent)* SectorSize), overridable via -cluster. - -hash prints only the root hash for scripting. Signed-off-by: Maksim An <maksiman@microsoft.com>
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Pull request overview
This PR extends the security policy tooling and library to support C-WCOW (Windows) policy generation using Block CIM digests, introduces a standalone blockcimdump inspection tool, and removes legacy JSON policy output in favor of Rego.
Changes:
- Add Windows container policy config/model support (
windows_container), plus Windows-specific policy/fragment marshalling APIs. - Update
securitypolicytoolto target Linux vs Windows (-os) and restrict output types to Rego/fragment. - Add Windows Block CIM digest computation helpers and a new
blockcimdumptool for inspecting sealed root hashes.
Reviewed changes
Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.
Show a summary per file
| File | Description |
|---|---|
| test/pkg/securitypolicy/policy.go | Add test helpers to build Base64 Windows policies from config opts. |
| pkg/securitypolicy/windows_tooling_test.go | Add unit tests for Windows container policy creation/marshalling and escaping. |
| pkg/securitypolicy/securitypolicy.go | Add WindowsContainerConfig + PolicyConfig.WindowsContainers and Windows container policy builder. |
| pkg/securitypolicy/securitypolicy_marshal.go | Make Rego the default marshaller; add Windows policy/fragment marshalling; improve string escaping. |
| pkg/securitypolicy/securitypolicy_internal.go | Add Windows containers to fragments and include MountedCim in internal conversion. |
| pkg/securitypolicy/opts.go | Add Windows container config opts and WithWindowsContainers. |
| internal/tools/securitypolicy/README.md | Update docs for Rego-only output and add C-WCOW usage/examples. |
| internal/tools/securitypolicy/main.go | Add `-os [linux |
| internal/tools/securitypolicy/helpers/windows.go | Implement Windows Block CIM digest computation via CIM APIs. |
| internal/tools/securitypolicy/helpers/windows_test.go | Add validation test for Windows container configs (requires image_name). |
| internal/tools/securitypolicy/helpers/windows_others.go | Provide non-Windows stub error for digest computation. |
| internal/tools/securitypolicy/helpers/helpers.go | Add Windows-container policy materialization from image-based configs. |
| internal/tools/blockcimdump/main.go | New CLI tool to inspect Block CIM metadata/root hash without CIM APIs. |
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| func TestMarshalWindowsPolicyRejectsJSON(t *testing.T) { | ||
| _, err := MarshalWindowsPolicy("json", false, nil, nil, nil, false, false, false, false, false, false, false, false) | ||
| if err == nil { | ||
| t.Fatal("expected JSON marshalling to be rejected for Windows policies") | ||
| } | ||
| } |
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Extend the securitypolicy package and tooling to generate rego policies for Confidential WCOW (Windows) images, mirroring the existing C-LCOW image-based flow. The runtime enforcement side (verified CIM mounts) already existed; this adds the authoring side so a matching policy can be produced from an image reference. Key changes: - pkg/securitypolicy: add WindowsContainerConfig (image-based) and CreateWindowsContainerPolicy, WithWindows* opts, and Windows rego/ fragment marshalling. Windows policy is rego only; the JSON marshaller is rejected for Windows. regoString() escapes backslashes/quotes so Windows paths and user strings survive marshalling. - internal/tools/securitypolicy: add -os linux|windows and route marshalling per OS; PolicyWindowsContainersFromConfigs fetches the windows platform image and computes verified Block CIM digests. - helpers/windows.go: import each layer into a verified single-file Block CIM and read its sealed root digest. Each layer is imported into its own directory with CimName "layer.cim" (merged: "merged.cim"), exactly matching containerd's cimfs snapshotter/differ, since the embedded CimName contributes to the sealed root digest. Setting SECURITYPOLICY_BLOCKCIM_DIR preserves the intermediate *.bcim for inspection. Existing LCOW policy generation behavior is intentionally preserved; the Windows path is only taken for windows_container config entries. Signed-off-by: Maksim An <maksiman@microsoft.com>
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Add Confidential WCOW security-policy generation + a block CIM root-hash dumper
Summary
This PR adds authoring-side support for generating Confidential WCOW (Windows) security policies, mirroring the existing C‑LCOW image-based flow, plus a small standalone tool for reading a block CIM's sealed root hash. The runtime enforcement side (verified CIM mounts) already existed; this fills in the policy-generation side so a policy can be produced from an image reference and will match what the runtime computes at mount time.
Motivation
For Confidential WCOW, a policy must pin each layer's verified Block CIM root digest. Getting that digest to match the runtime turned out to be subtle: the
CimNameembedded in a block CIM's PrimaryBlockTable contributes to the sealed root hash. containerd's cimfs snapshotter names every layer's CIMlayer.cim(each in its own directory) and the merged CIMmerged.cim; the tooling must reproduce this exactly, otherwise identical layer content yields a different digest. The blockcimdump tool was built to diagnose this on-disk and is included as a reusable debugging aid.Changes
securitypolicy: Confidential WCOW policy generationWindowsContainerConfig(image-based) andCreateWindowsContainerPolicy,WithWindows*options, and Windows rego/fragment marshalling. Windows policy is rego-only; the JSON marshaller is rejected for Windows and removed as a registered marshaller.regoString()escapes backslashes/quotes so Windows paths and user strings survive marshalling.-os linux|windowsflag routing marshalling per OS;PolicyWindowsContainersFromConfigsfetches the Windows-platform image and computes verified Block CIM digests.helpers/windows.go: imports each layer into a verified single-file Block CIM and reads its sealed root digest. Each layer is imported into its own directory withCimName = "layer.cim"(merged:"merged.cim"), matching containerd's snapshotter/differ exactly, since the embeddedCimNamecontributes to the digest.SECURITYPOLICY_BLOCKCIM_DIRpreserves the intermediate*.bcimfor inspection.windows_containerconfig entries.tools/blockcimdump: block CIM root-hash dumperlayer.vhdor the tooling's*.bcim) directly from on-disk metadata, without the Windows CIM APIs — the same valuecimfs.GetVerificationInforeturns.(1<<Exponent)*SectorSize,-clusteroverrides);-hashprints only the root hash; also dumps theBlockDeviceHeaderand PrimaryBlockTable (per-entryCimName+ content hash).Testing
go buildofpkg/securitypolicy/...,internal/tools/..., and the test module — clean.go test pkg.— pass.blockcimdump -hashagainst a containerdlayer.vhdreturns the expected sealed root digest; after theCimNamefix, the tooling-produced layer reproduces the same digest.