openhcl: persist trusted host certification evidence by harshvirMangla · Pull Request #3978 · microsoft/openvmm

harshvirMangla · 2026-07-20T10:54:14Z

Summary

Negotiate Trusted Host Certification support through the existing IGVM attestation request capability.
Parse both legacy AK certificate responses and versioned responses containing an AK certificate and Trusted Host Certification evidence.
Add an explicit host-certified TPM mode and persist the AK certificate and evidence in separate TPM NV indices.
Renew the AK certificate and evidence together while preserving existing legacy behavior.

Behavior

The feature is disabled by default.
Existing callers continue to use the legacy AK certificate response.
Host-certified requests require a complete wrapped response and fail closed on missing or malformed evidence.
AK certificate and evidence writes are preflighted and persisted together.
Cold boot behavior preserves evidence when TPM seeds remain stable.

Validation

Full x64 OpenHCL IGVM image build completed on a WSL-enabled development environment.
cargo check passed for all eight modified crates.
cargo clippy --all-targets passed for all eight modified crates.
cargo doc --no-deps passed for all eight modified crates.
Windows-runnable unit tests passed 12/12.
cargo xtask fmt --fix completed successfully.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: c6d204c3-77b3-451b-ad13-9c41472fc091

microsoft-github-policy-service · 2026-07-20T10:54:27Z

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Copilot

Pull request overview

This PR adds opt-in “Trusted Host Certification” support to the OpenHCL vTPM AK certificate provisioning flow by negotiating the capability via IGVM attestation, parsing a wrapped response that includes both an AK certificate and host-certification evidence, and persisting both pieces into TPM NV indices with appropriate boot/renewal behavior.

Changes:

Introduces a new HostCertified AK cert mode and plumbs an opt-in enablement bit/config through DPS management VTL feature flags and Underhill options.
Extends the IGVM attestation AK cert request/response protocol to optionally carry host-certification evidence (capability bitmap + versioned wrapped response).
Updates TPM NV allocation/renewal behavior to preserve or refresh the attestation-report NV index depending on AK cert mode, and adds unit tests for host-certified persistence.

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
vm/devices/tpm/tpm_lib/src/lib.rs	Makes attestation index size public and adds optional preservation of the attestation-report NV index across re-allocation.
vm/devices/tpm/tpm_device/src/resolver.rs	Adds resolver support for the new `HostCertified` AK cert resource variant.
vm/devices/tpm/tpm_device/src/lib.rs	Adds host-certified NV write validation + dual-index persistence, updates renewal logic, and adds unit tests/serialization guard.
vm/devices/tpm/tpm_device/src/ak_cert.rs	Introduces `HostCertified` mode, refactors attestation-report behaviors, and changes AK cert request return type to include optional evidence.
vm/devices/tpm/tpm_device/Cargo.toml	Adds `futures` as a dev-dependency for async test locking.
vm/devices/tpm_resources/src/lib.rs	Adds `HostCertified` variant to the TPM AK cert type resource model.
vm/devices/get/get_protocol/src/dps_json.rs	Adds `tvm_host_certification` feature bit and a unit test asserting opt-in bit placement.
petri/src/vm/hyperv/powershell.rs	Mirrors the new management VTL feature bit in Hyper-V flag plumbing.
openhcl/underhill_core/src/worker.rs	Plumbs host-certification enablement from env/options into DPS and AK cert type selection.
openhcl/underhill_core/src/options.rs	Adds `HCL_TVM_HOST_CERTIFICATION` option/env parsing.
openhcl/underhill_core/src/lib.rs	Wires the new option into worker launch configuration.
openhcl/underhill_core/src/emuplat/tpm.rs	Adds request-time flag propagation and returns structured AK cert + optional evidence from the host agent response.
openhcl/underhill_attestation/src/lib.rs	Re-exports the structured AK cert response type for consumers.
openhcl/underhill_attestation/src/igvm_attest/mod.rs	Adds a capability bit to request host-certification evidence and includes it in request generation.
openhcl/underhill_attestation/src/igvm_attest/ak_cert.rs	Implements parsing/validation for legacy vs wrapped host-certified AK cert responses and adds coverage tests.
openhcl/openhcl_attestation_protocol/src/igvm_attest/get.rs	Defines on-wire structs/constants for host-certification evidence wrapper and capability bit; increases AK cert response buffer size.
Cargo.lock	Adds `futures` to the resolved dependency set due to new dev-dependency usage.

+        if let Some(evidence) = evidence {
+            self.tpm_engine_helper
+                .write_to_nv_index(auth_value, TPM_NV_INDEX_ATTESTATION_REPORT, evidence)
+                .map_err(TpmErrorKind::WriteToNvIndex)?;


mingweishih · 2026-07-21T04:47:56Z

 /// Number of pages required by the response buffer of AK_CERT request
-/// Currently the AK cert request only requires 1 page.
-pub const AK_CERT_RESPONSE_BUFFER_SIZE: usize = PAGE_SIZE;
+pub const AK_CERT_RESPONSE_BUFFER_SIZE: usize = 2 * PAGE_SIZE;


I don't think this would work.

Thanks for flagging this. Could you clarify whether the concern is the one page AK_CERT contract or multi GPA handling in the production transport? I’ll verify that constraint before updating

It's the hard limit --- we currently only reserve one shared page for AK cert request/response.

mingweishih · 2026-07-21T22:40:20Z

+
+    let (response_header, _) = TvmHostCertificationResponseHeader::read_from_prefix(payload)
+        .map_err(|_| AkCertError::InvalidHostCertificationResponse)?;
+    let response_total_size = usize::try_from(response_header.total_size)


Are all these type conversions necessary? Can't const match the same type when possible?

mingweishih · 2026-07-21T22:40:48Z

+            payload[..size_of::<u32>()]
+                .try_into()
+                .expect("fixed-size slice"),
+        ) != TVM_HOST_CERTIFICATION_RESPONSE_MAGIC


I'd recommend putting the new logic into a separate helper function.

mingweishih · 2026-07-21T22:43:53Z

+
+    /// Returns true if the attestation report must be preserved across boot.
+    pub fn preserves_attestation_report(&self) -> bool {
+        matches!(self, TpmAkCertType::HostCertified(_, _))


attestation report is only relevant for HwAttested/SwAttested types.

mingweishih · 2026-07-21T22:45:49Z

+                TPM_NV_INDEX_AIK_CERT,
+                response.ak_cert.len(),
+            )?;
+            self.validate_host_certification_nv_write(


does this feature apply to isolated VMs?

mingweishih · 2026-07-21T22:47:36Z

                // Parse the response. Empty response indicates that the host agent is unavailable.
                let response = match result {
-                    Ok(data) if !data.is_empty() => {
-                        // Set the renew time if successfully receiving the data.


we should preserve the comments if it's just a refactoring.

mingweishih · 2026-07-21T22:49:20Z

Can you clarify if this feature applies to CVMs?

openhcl: persist trusted host certification evidence

060adf6

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: c6d204c3-77b3-451b-ad13-9c41472fc091

Copilot AI review requested due to automatic review settings July 20, 2026 10:54

Copilot started reviewing on behalf of harshvirMangla July 20, 2026 10:54 View session

Copilot AI reviewed Jul 20, 2026

View reviewed changes

Comment thread vm/devices/tpm/tpm_device/src/lib.rs

Comment on lines +1214 to +1217

if let Some(evidence) = evidence {

self.tpm_engine_helper

.write_to_nv_index(auth_value, TPM_NV_INDEX_ATTESTATION_REPORT, evidence)

.map_err(TpmErrorKind::WriteToNvIndex)?;

mingweishih reviewed Jul 21, 2026

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openhcl: persist trusted host certification evidence#3978

openhcl: persist trusted host certification evidence#3978
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harshvirMangla commented Jul 20, 2026

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