diff --git a/compos/src/compos_key_host_main.rs b/compos/src/compos_key_host_main.rs
deleted file mode 100644
index 28b069a..0000000
--- a/compos/src/compos_key_host_main.rs
+++ /dev/null
@@ -1,45 +0,0 @@
-// Copyright 2021, The Android Open Source Project
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-//! Run the CompOS key management service in the host, using normal Binder.
-
-mod compos_key_service;
-
-use crate::compos_key_service::CompOsKeyService;
-use anyhow::{Context, Result};
-use compos_aidl_interface::aidl::com::android::compos::ICompOsKeyService::BnCompOsKeyService;
-use compos_aidl_interface::binder::{add_service, BinderFeatures, ProcessState};
-use log::{info, Level};
-
-const LOG_TAG: &str = "CompOsKeyService";
-const OUR_SERVICE_NAME: &str = "android.system.composkeyservice";
-
-fn main() -> Result<()> {
-    android_logger::init_once(
-        android_logger::Config::default().with_tag(LOG_TAG).with_min_level(Level::Trace),
-    );
-
-    // We need to start the thread pool for Binder to work properly.
-    ProcessState::start_thread_pool();
-
-    let service = CompOsKeyService::new()?;
-    let service = BnCompOsKeyService::new_binder(service, BinderFeatures::default());
-
-    add_service(OUR_SERVICE_NAME, service.as_binder()).context("Adding service failed")?;
-    info!("It's alive!");
-
-    ProcessState::join_thread_pool();
-
-    Ok(())
-}
diff --git a/compos/src/compos_key_main.rs b/compos/src/compos_key_main.rs
new file mode 100644
index 0000000..9135c18
--- /dev/null
+++ b/compos/src/compos_key_main.rs
@@ -0,0 +1,72 @@
+// Copyright 2021, The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Run the CompOS key management service, either in the host using normal Binder or in the
+//! VM using RPC Binder.
+
+mod compos_key_service;
+
+use crate::compos_key_service::{CompOsKeyService, KeystoreNamespace};
+use anyhow::{bail, Context, Result};
+use binder::unstable_api::AsNative;
+use compos_aidl_interface::aidl::com::android::compos::ICompOsKeyService::BnCompOsKeyService;
+use compos_aidl_interface::binder::{add_service, BinderFeatures, ProcessState};
+use log::{info, Level};
+
+const LOG_TAG: &str = "CompOsKeyService";
+const OUR_SERVICE_NAME: &str = "android.system.composkeyservice";
+const OUR_VSOCK_PORT: u32 = 3142;
+
+fn main() -> Result<()> {
+    android_logger::init_once(
+        android_logger::Config::default().with_tag(LOG_TAG).with_min_level(Level::Info),
+    );
+
+    let matches = clap::App::new("compos_key_main")
+        .arg(clap::Arg::with_name("rpc_binder").long("rpc-binder"))
+        .get_matches();
+
+    let rpc_binder = matches.is_present("rpc_binder");
+
+    let key_namespace =
+        if rpc_binder { KeystoreNamespace::VmPayload } else { KeystoreNamespace::Odsign };
+    let service = CompOsKeyService::new(key_namespace)?;
+    let mut service =
+        BnCompOsKeyService::new_binder(service, BinderFeatures::default()).as_binder();
+
+    if rpc_binder {
+        info!("Starting RPC service");
+        // SAFETY: Service ownership is transferring to the server and won't be valid afterward.
+        // Plus the binder objects are threadsafe.
+        let retval = unsafe {
+            binder_rpc_unstable_bindgen::RunRpcServer(
+                service.as_native_mut() as *mut binder_rpc_unstable_bindgen::AIBinder,
+                OUR_VSOCK_PORT,
+            )
+        };
+        if retval {
+            info!("RPC server has shut down gracefully");
+        } else {
+            bail!("Premature termination of RPC server");
+        }
+    } else {
+        info!("Starting binder service");
+        add_service(OUR_SERVICE_NAME, service).context("Adding service failed")?;
+        info!("It's alive!");
+
+        ProcessState::join_thread_pool();
+    }
+
+    Ok(())
+}
diff --git a/compos/src/compos_key_service.rs b/compos/src/compos_key_service.rs
index 654eedd..66451b3 100644
--- a/compos/src/compos_key_service.rs
+++ b/compos/src/compos_key_service.rs
@@ -38,8 +38,17 @@
 use scopeguard::ScopeGuard;
 use std::ffi::CString;
 
+/// Keystore2 namespace IDs, used for access control to keys.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum KeystoreNamespace {
+    /// In the host we re-use the ID assigned to odsign. See system/sepolicy/private/keystore2_key_contexts.
+    // TODO(alanstokes): Remove this.
+    Odsign = 101,
+    /// In a VM we can use the generic ID allocated for payloads. See microdroid's keystore2_key_contexts.
+    VmPayload = 140,
+}
+
 const KEYSTORE_SERVICE_NAME: &str = "android.system.keystore2.IKeystoreService/default";
-const COMPOS_NAMESPACE: i64 = 101;
 const PURPOSE_SIGN: KeyParameter =
     KeyParameter { tag: Tag::PURPOSE, value: KeyParameterValue::KeyPurpose(KeyPurpose::SIGN) };
 const ALGORITHM: KeyParameter =
@@ -57,10 +66,11 @@
 const NO_AUTH_REQUIRED: KeyParameter =
     KeyParameter { tag: Tag::NO_AUTH_REQUIRED, value: KeyParameterValue::BoolValue(true) };
 
-const KEY_DESCRIPTOR: KeyDescriptor =
-    KeyDescriptor { domain: Domain::BLOB, nspace: COMPOS_NAMESPACE, alias: None, blob: None };
+const BLOB_KEY_DESCRIPTOR: KeyDescriptor =
+    KeyDescriptor { domain: Domain::BLOB, nspace: 0, alias: None, blob: None };
 
 pub struct CompOsKeyService {
+    namespace: KeystoreNamespace,
     random: SystemRandom,
     security_level: Strong<dyn IKeystoreSecurityLevel>,
 }
@@ -94,11 +104,12 @@
 }
 
 impl CompOsKeyService {
-    pub fn new() -> Result<Self> {
+    pub fn new(namespace: KeystoreNamespace) -> Result<Self> {
         let keystore_service = wait_for_interface::<dyn IKeystoreService>(KEYSTORE_SERVICE_NAME)
             .context("No Keystore service")?;
 
         Ok(Self {
+            namespace,
             random: SystemRandom::new(),
             security_level: keystore_service
                 .getSecurityLevel(SecurityLevel::TRUSTED_ENVIRONMENT)
@@ -107,6 +118,7 @@
     }
 
     fn do_generate(&self) -> Result<CompOsKeyData> {
+        let key_descriptor = KeyDescriptor { nspace: self.namespace as i64, ..BLOB_KEY_DESCRIPTOR };
         let key_parameters =
             [PURPOSE_SIGN, ALGORITHM, PADDING, DIGEST, KEY_SIZE, EXPONENT, NO_AUTH_REQUIRED];
         let attestation_key = None;
@@ -115,7 +127,7 @@
 
         let key_metadata = self
             .security_level
-            .generateKey(&KEY_DESCRIPTOR, attestation_key, &key_parameters, flags, &entropy)
+            .generateKey(&key_descriptor, attestation_key, &key_parameters, flags, &entropy)
             .context("Generating key failed")?;
 
         if let (Some(certificate), Some(blob)) = (key_metadata.certificate, key_metadata.key.blob) {
@@ -139,7 +151,11 @@
     }
 
     fn do_sign(&self, key_blob: &[u8], data: &[u8]) -> Result<Vec<u8>> {
-        let key_descriptor = KeyDescriptor { blob: Some(key_blob.to_vec()), ..KEY_DESCRIPTOR };
+        let key_descriptor = KeyDescriptor {
+            nspace: self.namespace as i64,
+            blob: Some(key_blob.to_vec()),
+            ..BLOB_KEY_DESCRIPTOR
+        };
         let operation_parameters = [PURPOSE_SIGN, ALGORITHM, PADDING, DIGEST];
         let forced = false;