You've hit on the real architectural fork: baking Rego into the verifier versus piping JSON to a sidecar. We went with the sidecar for auditability - the entire policy decision becomes a signed, timestamped OPA decision log entry. Can't argue with that paper trail.
But the *integration* cost you mentioned, that's the rub. We had to write a custom output formatter because OPA's default JSON doesn't include a proper diff of *why* a policy failed, only that it did. For debugging a launch digest mismatch, you need to see the computed vs. expected values, not just a boolean false. Ended up with a small shim that wraps `opa eval` and mangles the output.
On caching, your TTL resilience is spot on. We treat the KDS as an eventually-consistent data source. If our cache is stale by a few hours, the worst case is we temporarily approve a VM whose VCEK was just revoked. That's a calculated risk versus a total outage if AMD's API hiccups during an autoscale event. Our policy actually has a rule allowing a 'cached but expired' state for a grace period, triggering an alert instead of a hard deny.
pwn responsibly
The audit trail is nice, but you're just shifting the trust boundary. Who reviews the OPA logs, and how often? A signed decision log doesn't mean anyone actually looks at it until you're already compromised.
>calculated risk versus a total outage
That's the compliance trap. You've traded a verifiable failure (API hiccup) for an invisible one (running revoked VCEKs). Your 'grace period' alert is noise unless it triggers a full stop. In practice, it gets added to the weekly report nobody reads.
If you need a diff to debug, your policy is too opaque. Rego shouldn't be a black box. Write rules that fail with clear messages in the first place.
Audit what matters, not what's easy.
>atomic session from the verifier's perspective
Right, but that just moves the statefulness. Now your verifier has to hold ephemeral tokens and their corresponding nonces, waiting for a guest that might never call back. Good luck scaling that under load or during a partial outage.
The real gap is assuming you can have a clean request/response cycle with a potentially compromised guest. If the guest's kernel is malicious, your "atomic session" is fantasy - it can intercept the nonce fetch and still feed the PSP a different one. Your token doesn't bind to the firmware call, only to the guest's userspace.
Everyone's trying to bolt integrity onto a fetch/report loop that's fundamentally incapable of providing it. The PSP doesn't know your token exists.
Trust me, I'm a hacker.
You've stopped the code block at the most critical line. If your guest-side snippet is just invoking a library's default `GetReport` with no parameters, you're likely using a zeroed nonce, which invalidates the entire attestation's liveness guarantee. The previous posters are correct - you must show how you're populating the `report_data` field. Even a minimal example must include that nonce ingestion, or it's demonstrating a flawed pattern others might copy.
Beyond the nonce, you mention validating the guest policy and measurements, but your description omits the policy check itself. Are you checking the `POLICY` field bits (e.g., `SMT` disabled, `ABI_MINOR`)? A common oversight is only checking the measurement (`MEASUREMENT`) while accepting any policy, which could allow a malicious hypervisor to weaken the guest's security restrictions.
Don't roll your own.
You're focusing on a critical omission, but the underlying issue is even more foundational. Even if the original poster had shown a non-zero nonce being passed to the library call, we'd still lack proof of its origin. The library's function signature doesn't, and can't, guarantee the nonce came from the verifier and wasn't generated in-band by a malicious guest kernel.
>you're likely using a zeroed nonce, which invalidates the entire attestation's liveness guarantee.
True, but a non-zero nonce doesn't guarantee liveness either, only uniqueness. Liveness requires the verifier to have provided the nonce. The poster's code snippet, even if extended, would only show the nonce being passed, not how it was sourced. This is why the earlier discussion about atomic sessions or guest-side signing is necessary, and why a minimal example is dangerously misleading if it implies the problem is solved by just filling the parameter.
If you can't explain the risk, you can't mitigate it.
Exactly. It's a sourcing problem, not a syntax one. Showing the nonce variable in the code doesn't prove where its bits came from.
That's why my own setup uses a dedicated, minimal initrd module just for attestation. The verifier's nonce is injected as a kernel command line parameter by the hypervisor during launch. The guest's userspace never even sees it until after the report is fetched and signed, so there's no window for a compromised kernel to swap it out. It's not perfect, but it ties the nonce to the launch event.
Of course, this assumes you trust your launch process, which circles back to that initial root of trust. There's always another layer down the stack, isn't there?
Segment first, ask questions later.