Alright, I've been deep in the weeds this week trying to get our Rust-based agent to properly generate and verify attestation reports inside an Intel TDX enclave. The goal was to have the agent, upon startup, produce a local attestation quote, then use the Intel TDX Quote Provider Library (QPL) to convert that into a verifiable remote attestation report for our central verifier. The documentation felt a bit... scattered, so here’s my hands-on walkthrough, including the performance hit I measured.
First, the big picture: You can't get a remotely verifiable quote directly from the guest. The flow is:
1. Agent runtime inside TDX guest generates a **local attestation report** (a `REPORT` structure).
2. This report, specifically its `REPORTDATA` field (the first 64 bytes), contains a hash of our agent's critical code and its public key.
3. The guest makes a call (via `TDCALL[TDG.MR.REPORT]`) to the TDX Module to generate this report targeting the **Quoting Enclave (QE)** as the target.
4. We then need to pass this local report to the **TDX Quote Provider Library** (running in the host, not the guest) to convert it into a **TDX Quote**.
5. This quote is what we send to our remote verifier (like Intel's PCCS or our own service) for final validation.
The tricky part is step 4. The QPL isn't a simple library you link into your guest agent. It's a host-side service. So our enclaved agent needs a secure channel to request quote generation from the host. In our setup, we used a simple vsock channel for this request/response.
Here's the core of our Rust code that constructs the local report for the QE. We used the `tdx-tdcall` crate for the `tdcall` invocation:
```rust
use tdx_tdcall::tdcall;
fn generate_local_report_for_qe(
report_data: &[u8; 64],
target_info: &TARGET_INFO, // QE's TARGET_INFO, obtained via a prior call
) -> Result {
let mut report: REPORT = Default::default();
let mut td_report_mac_struct = TD_REPORT {
report: &mut report as *mut REPORT,
report_size: size_of::() as u32,
report_mac: [0u8; 32],
};
// Prepare REPORTDATA (e.g., hash of our public key and code)
report.reportdata[..64].copy_from_slice(report_data);
// Copy QE's TARGET_INFO
report.targetinfo = *target_info;
unsafe {
match tdcall::td_report(&mut td_report_mac_struct) {
Ok(_) => Ok(report),
Err(e) => Err(TdxError::from(e)),
}
}
}
```
Once we have the local `REPORT`, we serialize it and send it via vsock to a host-side daemon we wrote. This daemon uses the **QPL** (`libtdx_attest.so`) to generate the final quote:
```c
// Excerpt from our host-side service (C)
tdx_attest_error_t err = tdx_att_get_quote(
(const uint8_t *)&local_report_buffer, // Our serialized REPORT from the guest
sizeof_local_report,
NULL, 0, // p_supplemental_data is optional
"e_buffer,
"e_size,
&supplemental_data_size
);
```
**Performance & Operational Notes:**
* The round-trip (guest local report -> vsock -> host QPL -> vsock -> guest) added a **consistent 80-110ms** overhead to our agent's startup sequence. This is on a 3rd Gen Xeon Scalable (Ice Lake) with the host service pre-initialized.
* You **must** provision the host with the QPL and the PCCS client configured correctly. The QPL needs to fetch certs from Intel's PCCS. If PCCS is unreachable, cached certs are used, but initial setup is a dependency.
* We're now exporting this latency as a Prometheus gauge: `agent_attestation_duration_seconds`. It's a great canary for TEE health.
**Where this fits:** For regulated deployments where you need hardware-backed attestation to a specific known TCB (like a bank's audit requirement), this flow is non-negotiable. The operational complexity is high—you're managing a host-side service *and* the guest agent. If you don't need per-agent hardware proofs, something like AWS Nitro Enclaves (with its simpler KMS integration) might be less ops-heavy.
Has anyone else built a similar pipeline? I'm particularly curious if you've found ways to cache or batch these quote generation calls to amortize the cost for short-lived agent tasks. Also, any gotchas with the supplemental data field validation?
- Aisha