aproxy: decouple KBS backend and shift runtime_data hashing from kernel

Documentation/docs/developer/ATTESTATION.md

@@ -12,6 +12,7 @@
     - [Host Proxy Diagram](#host-proxy-diagram)
   - [Transport Methods](#transport-methods)
   - [Try for yourself](#try-for-yourself)
+  - [Try with Trustee KBS](#try-with-trustee-kbs)
 <!--toc:end-->
 
 ## Background
@@ -53,35 +54,22 @@ tuple [MAJOR, MINOR, PATCH]. The current version is 0.1.0.
 - `tee`: The TEE hardware architecture that SVSM is running on.
 
 The proxy will then complete the negotiation phase with the remote attestation
-server and reply with a list of negotiation parameters that must be included in
-the attestation evidence.
+server and reply with a challenge nonce that must be included in the attestation evidence.
 
 A `NegotiationResponse` is sent from the proxy to SVSM.
 An example `NegotiationResponse` is shown below.
 ```json
 {
     "challenge": "oFlY92ZdS3ymzxokYuDzxw==\",
-    "params": [
-                "EcPublicKeyBytes",
-                "Challenge"
-              ]
+
 }
 ```
 - `challenge`: The challenge nonce returned by the remote attestation server
 that will likely need to be hashed into the attestation evidence to ensure
 freshness. Represented as variably-sized array of bytes.
-- `params`: The negotiation parameters. Each `NegotiationParam` represents some
-form of data that must be hashed into the attestation evidence. This hash will
-be reconstructed by the remote attestation server when the evidence is presented
-from SVSM.
-
-The valid negotiation parameters are as follows:
-- `Challenge`: The bytes represented in the `challenge`.
-- `EcPublicKeyBytes`: The byte buffers of the public key's x and y coordinates
-(in that order).
 
-SVSM can then collect the attestation evidence (with the negotiation parameters
-embedded within the report data) and continue to the attestation phase.
+aproxy builds the entire KBS runtime JSON object, hashes it on the host using Sha384,
+and returns the hash as a single challenge for SVSM to put in its report.
 
 ### Attestation Phase
 
@@ -146,7 +134,7 @@ example).
 
 Valid evidence formats are the following:
 - `Snp`: SEV-SNP
-    - `report`: Attestation report bytes.
+    - `attestation_report`: Attestation report bytes.
     - `certs_buf`: Optional byte buffer representing SEV-SNP certificate chain
                    (ARK, ASK, VEK) set by the host hypervisor.
 
@@ -387,3 +375,8 @@ SEV-SNP machine with an SVSM-enabled kernel.
     cd kbs-test
     cargo run -- --measurement 9ef6c500d19addcd5937c6c8bd4e51b1893f048eea03d5407cfb0692c06615e3f6c044c667c32e520913d93234e836fe
     ```
+
+## Try with Trustee KBS
+
+You can also try with the official Trustee KBS and SVSM setup. See [KBS-SVSM](KBS-SVSM.md)
+

Documentation/docs/developer/KBS-SVSM.md

@@ -0,0 +1,201 @@
+# Attestation in SVSM using Trustee KBS
+
+We need,
+1. SVSM (with attest feature),
+    > git clone https://github.com/coconut-svsm/svsm.git
+2. The aproxy on the host.
+3. Trustee KBS server (For now, the KBS softhsm container, is not upstream)
+    > git clone https://github.com/armenon-rh/trustee.git
+
+This document explains the steps to perform a complete attestation.
+
+# Prerequisites & Architectural Overview
+The Key Broker Service (KBS) handles confidential computing attestation and secret provisioning. Depending on your security requirements, it can be deployed in one of the two modes:
+
+## Mode A: Resource Key-Value Storage Backend (Default)
+Act as a direct storage repository for secrets.
+- Flow: SVSM <--> aproxy <--> KBS (Resource kvstorage backend)
+- Concept: The user provisions a secret into the KBS storage via kbs-client. SVSM later presents its attestation token to retrieve that raw secret.
+
+## Mode B: PKCS#11 Plugin Backend (softHSM)
+Offloads cryptographic operations and key management to a Software HSM.
+- Flow: SVSM <--> aproxy <--> KBS(PKCS#11 plugin) <--> softHSM
+- Concept: The user generates a 32-byte symmetric key, which softHSM wraps (encrypts) using its internal public key. The user uses the raw key to encrypt vTPM state, but implants the wrapped key into the metadata header. During boot, SVSM hands the wrapped key to KBS, which requests softHSM to unwrap it, passing back the raw key only after attestation.
+
+# Step by Step implementation
+
+## 1. Build the image
+
+An Ubuntu based KBS container image that also has softHSM and opensc (pkcs11-tool to interact with softHSM) packages installed.
+
+```bash
+cd trustee/
+podman build -t kbs-service -f kbs/docker/kbs-softhsm-pkcs11/Dockerfile .
+```
+
+## 2. Initialize Host storage directories
+
+Create the required host workspaces to persist softHSM tokens and KBS resource assets
+
+```bash
+mkdir -p $HOME/kbs-workspace/softhsm_tokens
+mkdir -p $HOME/kbs-workspace/kbs-storage
+```
+
+## 3. Configure Attestation Policy
+Create the repository directory and establish the Open Policy Agent (OPA) Rego policy file that dictates KBS access rules.
+
+```bash
+mkdir -p kbs-workspace/repository/kbs && cd kbs-workspace/repository/kbs
+
+cat <<EOF > resource-policy.rego
+package policy
+
+default allow = false
+
+allow if {
+    true
+}
+EOF
+
+cd -
+```
+
+## 4. Run the KBS container
+Choose the configuration profile that fits your desired operational mode:
+
+### Option A: Run as Resource Backend (KV Storage)
+
+```bash
+podman run -d \
+    --name kbs-pkcs11-service \
+    -p 8080:8080 \
+    -v $HOME/kbs-workspace/repository/kbs/resource-policy.rego:/etc/kbs/repository/kbs/resource-policy.rego:Z \
+    -v $HOME/kbs-workspace/kbs-storage/:/opt/confidential-containers/storage:Z \
+    kbs-service:latest /usr/local/bin/kbs --config-file /etc/kbs/kbs-config-resource.toml
+```
+
+### Option B: Run as PKCS#11 Plugin Backend
+```bash
+podman run -d \
+    --name kbs-resource-service \
+    -p 8080:8080 \
+    -v $HOME/kbs-workspace/softhsm_tokens/:/var/lib/softhsm/tokens:Z \
+    -v $HOME/kbs-workspace/repository/kbs/resource-policy.rego:/etc/kbs/repository/kbs/resource-policy.rego:Z \
+    -v $HOME/test/trustee/kbs/docker/kbs-softhsm-pkcs11/config_pkcs11.toml:/etc/kbs/kbs-config.toml \
+    kbs-service:latest
+```
+
+## 5. Generate Cryptographic assets
+```bash
+openssl rand 32 > rand.bin
+echo "My secret" > secret.txt
+```
+The secret will be stored in kbs resource backend, whereas if we want to use the pkcs11 plugin then the key will be wrapped.
+
+## 6. Provision or Wrap the cryptographic assets
+
+### Option A: Store Secret in Resource Backend
+
+```bash
+make -C kbs cli FEATURES
+./target/release/kbs-client --url http://0.0.0.0:8080 config  set-resource --path default/sample/test --resource-file secret.txt
+```
+The secret will be store in KBS.
+
+### Option B: Wrap Key via PKCS#11 Plugin
+```bash
+curl -X POST http://0.0.0.0:8080/kbs/v0/pkcs11/wrap-key \
+     -H "Content-Type: application/octet-stream" \
+     --data-binary @rand.bin \
+     --output wrapped_rand.bin
+```
+wrapped_rand.bin will contain the wrapped key
+
+## 7. Use [tpm provisioner](https://github.com/armenon-rh/tpm_provisioner) to create an NVChip file
+
+```bash
+cd ../
+git clone https://github.com/armenon-rh/tpm_provisioner.git && cd tpm_provisioner
+
+podman build -t tpm-provisioner -f Dockerfile .
+
+podman run -it --name tpm-lab tpm-provisioner
+
+cargo run && verify
+
+# Generate the ek public key from tpm, store it in ek.pub --> 1
+tpm2_createek -T mssim:host=localhost,port=2321 -c ek.ctx -u ek.pub -G rsa
+
+# print the public part of it the endorsement key  --> 2
+tpm2_print -t TPM2B_PUBLIC ek.pub
+
+# Retrieve the certificate from nvram, in DER format --> 3
+tpm2_nvread -T mssim:host=localhost,port=2321 -C o 0x1c00002 -o ek_cert.der
+
+# Extract public key from certificate, in PEM format --> 4
+openssl x509 -in ek_cert.der -inform DER -pubkey -noout > cert_key.pem
+
+# print the public key, modulus will be printed --> 5
+openssl rsa -pubin -in cert_key.pem -text -noout
+
+# modulus in 2 and 5 should match!
+
+# copy the important files to host
+# ek_cert.der, ek_cert.pem, local_ca.pem, cert_key.pem, NVChip
+podman cp tpm-lab:/app/tpm_provisioner/<file_name> /path/on/host/<file_name>
+
+```
+
+## 8. Use [vtpm-to-svsm-blk](https://github.com/armenon-rh/vtpm-to-svsm-blk) to create a virtio block image
+- use rand.bin from step 5 as key for encryption param
+- use wrapped_rand.bin from step 6 as wrapped key param
+vtpm_state.img is ready, which has payload encrypted and a header with the wrapped key.
+
+```bash
+git clone https://github.com/armenon-rh/vtpm-to-svsm-blk.git && cd vtpm-to-svsm-blk
+
+cargo build
+
+cargo run -- -k rand.bin -w wrapped_rand.bin -s /path/on/host/<NVChip> -o /path/on/host/to/store/vtpm_state.img
+
+# This will create a vTPM image, that can be attached to SVSM as a virtio block
+
+```
+
+## 9. Run Aproxy on the host
+
+```bash
+cd svsm/
+make aproxy
+./bin/aproxy --protocol kbs \
+    --url http://0.0.0.0:8080 \
+    --unix /tmp/svsm-proxy.sock \
+    --force > aproxy.log 2>&1 &
+```
+
+## 10. Launch the confidential guest
+
+Assuming that qemu is compiled using the [svsm](https://github.com/coconut-svsm/qemu.git) branch and SVSM is compiled using the latest [OVMF.FD file](https://github.com/coconut-svsm/edk2.git), and the fedora image is built using [image builder](https://github.com/stefano-garzarella/snp-svsm-vtpm/blob/main/build-vm-image.sh)
+
+```bash
+./scripts/launch_guest.sh --aproxy /tmp/svsm-proxy.sock \
+    --qemu $HOME/test/qemu/bin/qemu-system-x86_64 \
+    --image $HOME/test/snp-svsm-vtpm/images/fedora-luks.qcow2 \
+    --state ../vtpm_state.img
+```
+
+Note: Make sure to add the option --pcd PcdUninstallMemAttrProtocol=TRUE while building edk2 for Fedora 42 images
+
+```bash
+export PYTHON3_ENABLE=TRUE
+export PYTHON_COMMAND=python3
+make -j16 -C BaseTools/
+source ./edksetup.sh --reconfig
+build -p OvmfPkg/OvmfPkgX64.dsc -a X64 \
+      -b DEBUG -t GCC \
+      -D DEBUG_ON_SERIAL_PORT \
+      -D DEBUG_VERBOSE \
+      -D TPM2_ENABLE
+      --pcd PcdUninstallMemAttrProtocol=TRUE
+```

kernel/src/attest.rs

@@ -33,7 +33,6 @@ use cocoon_tpm_utils_common::{
 use kbs_types::Tee;
 use libaproxy::*;
 use serde::Serialize;
-use sha2::{Digest, Sha512};
 use zerocopy::{FromBytes, IntoBytes};
 
 // TODO: Make the IO port configurable/discoverable or drop the support entirely.
@@ -128,6 +127,19 @@ impl TryFrom<Tee> for AttestationDriver<'_> {
 }
 
 impl AttestationDriver<'_> {
+    /// Extracts the public key coordinates as a TPM ECC point from the internal `EccKey`.
+    fn get_tpm_pub_key(&self) -> Result<TpmsEccPoint<'static>, AttestationError> {
+        let curve =
+            Curve::new(self.ecc.pub_key().get_curve_id()).map_err(AttestationError::Crypto)?;
+
+        let curve_ops = curve.curve_ops().map_err(AttestationError::Crypto)?;
+
+        self.ecc
+            .pub_key()
+            .to_tpms_ecc_point(&curve_ops)
+            .map_err(AttestationError::Crypto)
+    }
+
     /// Attest SVSM's launch state by communicating with the attestation proxy.
     pub fn attest(&mut self) -> Result<SecretSlice, SvsmError> {
         let negotiation = self.negotiation()?;
@@ -139,9 +151,12 @@ impl AttestationDriver<'_> {
     /// that should be included in attestation evidence (e.g. through SEV-SNP's REPORT_DATA
     /// mechanism).
     fn negotiation(&mut self) -> Result<NegotiationResponse, AttestationError> {
+        let pub_key = self.get_tpm_pub_key()?;
+
         let request = NegotiationRequest {
             version: (0, 1, 0), // Only version supported at present.
             tee: self.tee,
+            key: (self.ecc.pub_key().get_curve_id(), &pub_key).into(),
         };
 
         self.write(request)?;
@@ -154,16 +169,9 @@ impl AttestationDriver<'_> {
     /// containing the status (success/fail) and an optional secret returned from the server upon
     /// successful attestation.
     fn attestation(&mut self, n: NegotiationResponse) -> Result<SecretSlice, AttestationError> {
-        let curve =
-            Curve::new(self.ecc.pub_key().get_curve_id()).map_err(AttestationError::Crypto)?;
+        let pub_key = self.get_tpm_pub_key()?;
 
-        let pub_key = self
-            .ecc
-            .pub_key()
-            .to_tpms_ecc_point(&curve.curve_ops().map_err(AttestationError::Crypto)?)
-            .map_err(AttestationError::Crypto)?;
-
-        let evidence = evidence(&self.tee, hash(&n, &pub_key)?)?;
+        let evidence = evidence(&self.tee, prepare_report_data(&n)?)?;
 
         let req = AttestationRequest {
             tee: self.tee,
@@ -397,26 +405,9 @@ fn evidence(tee: &Tee, hash: Vec<u8>) -> Result<AttestationEvidence, Attestation
     Ok(evidence)
 }
 
-/// Hash the negotiation parameters from the attestation server for inclusion in the
-/// attestation evidence.
-fn hash(
-    n: &NegotiationResponse,
-    pub_key: &TpmsEccPoint<'static>,
-) -> Result<Vec<u8>, AttestationError> {
-    let mut sha = Sha512::new();
-
-    for p in &n.params {
-        match p {
-            NegotiationParam::Challenge => {
-                sha.update(&n.challenge);
-            }
-            #[allow(irrefutable_let_patterns)]
-            NegotiationParam::EcPublicKeyBytes => {
-                sha.update(&*pub_key.x.buffer);
-                sha.update(&*pub_key.y.buffer);
-            }
-        }
-    }
-
-    try_to_vec(&sha.finalize()).or(Err(AttestationError::VecAlloc))
+/// Take 48 byte negotiation challenge nonce from aproxy into 64 byte array required for the TEE attestation evidence report
+fn prepare_report_data(n: &NegotiationResponse) -> Result<Vec<u8>, AttestationError> {
+    let mut report_data = [0u8; 64];
+    report_data[..48].copy_from_slice(&n.challenge);
+    Ok(report_data.to_vec())
 }

libaproxy/src/negotiation.rs

@@ -18,15 +18,7 @@ pub struct NegotiationRequest {
     /// Version of the attestation protocol, represented as semver (MAJOR.MINOR.PATCH).
     pub version: (u32, u32, u32),
     pub tee: kbs_types::Tee,
-}
-
-/// A parameter that must be hashed into the negotiation hash.
-#[derive(Serialize, Deserialize, Debug)]
-pub enum NegotiationParam {
-    /// Hash the challenge returned from attestation server.
-    Challenge,
-    /// Hash the EC public key's `Elliptic-Curve-Point-to-Octet-String` encoding.
-    EcPublicKeyBytes,
+    pub key: EcP256PublicKey,
 }
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -37,6 +29,4 @@ pub struct NegotiationResponse {
         deserialize_with = "deserialize_base64"
     )]
     pub challenge: Vec<u8>,
-    /// Parameters to be hashed in the specific order defined by the array
-    pub params: Vec<NegotiationParam>,
 }

tools/aproxy/Cargo.toml

@@ -16,6 +16,8 @@ libaproxy.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 vsock = "0.5.1"
+sha2 = { workspace = true }
+sev = { version = "8.0.0", features = ["snp", "serde"] }
 
 [lints]
 workspace = true