Renew Attestation Policy After Measurement Mismatch

When a VM's attestation fails with a measurement mismatch error, it means the firmware measurement reported by the VM no longer matches the expected ("golden") measurement stored in Vault. This typica

Identifying the Problem

A failed attestation event looks like this:

json

{
  "Success": false,
  "Message": "verify: gcp-sev-snp-raw: measurement did not match, found: 12068361...6a3a5, expected: 7a5ed176...2434e",
  "Instance": "1f96b38e-331b-49dc-bcf8-342480abcafe",
  "resourceModel": "Virtual-machine"
}

The key fields:

• Success: false — attestation verification failed.

• Message — contains both the found (actual) measurement and the expected measurement currently stored in Vault.

• Provider — the attestation provider (e.g., gcp-sev-snp-raw, azure-sev-snp-vtpm, aws-sev-snp-raw).

Understanding createPolicy.js

The script scripts/common/vault/createPolicy.js is used to create or update the trusted attestation appraisal policy in Vault. It defines the "golden" measurements that Vault uses to verify a VM when it requests attestation.

Running this script with the new measurement effectively renews the attestation baseline that all future VMs of that configuration will be verified against.

What the Script Does

1. Validates the provided cloud provider (-cp) and measurement (-mt) arguments.

2. Connects to Vault and the database.

3. Gathers current policy names from the database and Vault.

4. Parses the -name argument to derive the firmware identity name.

5. Prompts for confirmation before making changes.

6. Updates Vault:

   • Creates (or overwrites) a firmware identity containing the new measurement.

   • Creates (or overwrites) the appraisal policy linking to the firmware identity and the correct hardware trust path based on the cloud provider.

Trust Path Mapping

Cloud Provider	Hardware Trust Path
Azure	AMD_SEV_SNP_MILAN_VCEK
GCP	AMD_SEV_SNP_MILAN_VCEK
AWS	AMD_SEV_SNP_MILAN_VLEK

Usage

Parameters

Flag	Description	Example
-cp	Cloud provider name	AZURE, AWS, GCP
-mt	The new firmware measurement hash	12068361369cf917...
-name	Full policy identifier: [provider]_[size]_[image]	gcp_n2d-standard-2_ubuntu

Example: Renewing a GCP Policy

Given this failed attestation:

found:    12068361369cf9179bb6ac08572b7e15ed0bc8abb698cb04d4f584f7ff512a4c2081c1f5b105351dbd45c035a7d6a3a5
expected: 7a5ed176bad8a9ff02cebb94b24b076a0b1905042a85d9fca7670d3a3ff466db3b1c2b76f8eca888f8d806d2ec92434e

Run the following to update Vault with the new measurement:

bash

node scripts/common/vault/createPolicy.js \
  -cp=GCP \
  -mt=12068361369cf9179bb6ac08572b7e15ed0bc8abb698cb04d4f584f7ff512a4c2081c1f5b105351dbd45c035a7d6a3a5 \
  -name=gcp_n2d-standard-2_ubuntu

The script will prompt you to type y to confirm.

Example: Renewing an Azure Policy

bash

node scripts/common/vault/createPolicy.js \
  -cp=AZURE \
  -mt=<new-measurement-hash> \
  -name=azure_standard-dc4as-v5_ubuntu

Example: Renewing an AWS Policy

bash

node scripts/common/vault/createPolicy.js \
  -cp=AWS \
  -mt=<new-measurement-hash> \
  -name=aws_m6a-large_ubuntu

After Renewal

Once the policy is updated in Vault, the VM's next attestation cycle will use the new expected measurement. No VM restart is required — the attestation will succeed on the next scheduled check.

Important Notes

• The -name must match the existing policy name exactly. Use the format [provider]_[size]_[image].

• This script updates the policy for all VMs of that provider/size/image combination, not just a single VM instance.

• Always verify the new measurement is legitimate (e.g., from a known firmware update) before accepting it into Vault.