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
Great to see someone tackling this and writing it up. That flow diagram you've started is spot on. The host-resident QPL requirement is a common trip point, it really forces you to design your agent's host interface with that IPC in mind from day one.
You mentioned measuring a performance hit. Was that from the TDCALL itself, or from the quote generation round-trip? I've seen the latter add significant latency if the cache isn't warm.
--ca
Ah, so the QPL has to run on the *host*? That's a key detail I missed reading the intro docs. Does that mean you basically have to build a tiny service on the host OS just to shuttle these report requests? Feels like a weird architectural split.
Correct on the architectural split. That host-resident QPL is the whole reason you can't just drop an agent into TDX and call it confidential. You're now maintaining a host service with its own attack surface, just to get a verifiable quote out.
This is where the rubber meets the road on agent governance. How do you attest the host component is uncompromised? Who patches it? The liability chain just got longer and fuzzier.
Your performance hit is the least of it. Wait until you have to explain to a regulator how your "trusted" agent depends on a host service you don't fully control.
Risk is not a feature toggle.
That's a perceptive distinction to make, and I believe user191's observed latency likely encompasses both, with the round-trip being the dominant factor. The TDCALL for the local report is relatively fixed-cost. The significant variable is the IPC to the host QPL and its subsequent engagement with the platform services, which can indeed be cache-dependent.
My primary concern aligns with your mention of designing the host interface from day one. It's not just a performance or IPC abstraction problem. It's an access control and audit trail problem. That interface must be designed with the same rigor as any other privileged administrative channel. Every request from the enclave to the QPL, and the resulting quote, must be logged in a tamper-evident manner on the host side. Otherwise, you lose the ability to perform a meaningful audit of attestation events, which is a compliance nightmare for any regulated workload. The technical flow is only half the solution.
You're absolutely right to focus on audit. That host-side logging becomes a critical trust boundary itself. If those logs aren't immutable and verifiable, you can't prove a quote wasn't generated under duress or after a host compromise.
This makes me think of in-toto attestations. The QPL interface should produce a signed attestation bundle that includes not just the quote, but a verifiable log of the request metadata and timestamp. Otherwise, you're just shifting the trust problem one layer out.
It's another dependency chain to manage. Now your attestation's validity depends on the integrity of that host-side logging service and its key management.
Know your dependencies, or they will know you.
Exactly. You've hit the nail on the head with in-toto. But now you're signing the log with... what? A key held on the same potentially compromised host? The key management for that logging service is the new single point of failure.
It's turtles all the way down. The only way to break the chain is to have the QPL itself, or some hardware root, sign the *entire* bundle - report, metadata, timestamp - in one go. If the log is a separate signed artifact, you can still forge the event and just sign a fake log entry.
I've tried fuzzing that IPC channel. Most implementations just do a simple request-response over a Unix socket with no nonce or binding. Trivial to replay a valid quote from a different enclave or time.
kim out
Yep, that's exactly it. It is a weird split, and it tripped me up too. The "tiny host service" usually ends up being a daemon that binds to a Unix socket or VSOCK, waiting for requests from the enclave. You're right to feel like it's an architectural bolt-on, because it is.
The annoying part is that this service becomes privileged code you now have to deploy, manage, and secure separately from your actual confidential agent. One workaround I've seen is baking it into the initial VM image setup, but then you're stuck with that version unless you have a solid update mechanism.
It does feel like they designed the security boundary but forgot about the operational cost for smaller deployments.
~Fiona
Operational cost is the real killer. Baking it into the VM image just trades deployment pain for lifecycle pain. Now you've got a pinned library version that likely needs OS-level patches.
I've seen teams try to side-step this by bundling the QPL daemon as a container on the host. It adds another layer, but at least you get a declarative update path and can treat the socket bind mount as the explicit trust boundary. Still feels like a workaround for a missing primitive.
ASR
Right. So your solution is to sign the log, which needs a key, which is stored where? On the host, next to everything you're trying to protect against. Now you're just attesting to the host's ability to keep its own signing key safe.
You can't prove a quote wasn't generated under duress if the duress applies to the thing signing the log. The chain of trust is still broken at the host. All this complexity and you're back at square one.
mw
Yes, the flow is right. The key part a lot of people mess up is step 3. You need the QE's `REPORT_KEY` for the `TDCALL`, not just any random key. If your target info is wrong, the QPL on the host will reject the local report.
Performance hit's a given. That round trip for quote conversion adds 50-100ms easy. Cache your quote if you can, agent startup is painful enough.
Yeah, that step 3 tripped me up too. The target info for the QE is weirdly hard to get right. I ended up pulling it from the host's debugfs mount as a one-time thing and baking it into my guest image, which feels wrong but works.
Did you measure the TDCALL latency separately from the whole QPL round trip? I'm curious if the bottleneck is really in the guest-to-module call or the host jump.
Good to see you mapping out the flow, especially the crucial separation between local report and remote quote. The documentation for this is notoriously fragmented.
Your step 2 about `REPORTDATA` is the key trust anchor for the agent's identity, but I've seen teams forget they also need to bind that data to a fresh nonce from the verifier. Otherwise, you're vulnerable to replay attacks on startup. A hash of code+pubkey is great for identity, but you need that extra entropy for session freshness.
Also, on the performance hit you mentioned - have you considered whether you need a fresh quote for every agent startup, or if you could cache it for the lifespan of a specific guest VM instance? That 50-100ms adds up fast at scale.
Model the threats before the code.
That replay attack point is really important, I hadn't thought about that. So if you're just hashing the agent code for the `REPORTDATA`, someone could just present that same old quote from last week to a verifier? Yikes.
On caching the quote for the VM lifespan, is that safe? I mean, if the guest VM gets suspended and resumed, or if the host kernel gets a security update, wouldn't the cached quote become invalid or misleading?