Define and implement a service for key management in CompOS.
This is based on the interface prototyped in
system/security/ondevice-signing/FakeCompOs.h.
For now, to allow manual testing, this is a standalone binary.
Bug: 191763370
Test: Builds.
Change-Id: I307ba9144fa51cca7ebee2142980f3a1cd436ef2
diff --git a/compos/src/compos_key_service.rs b/compos/src/compos_key_service.rs
new file mode 100644
index 0000000..97fd855
--- /dev/null
+++ b/compos/src/compos_key_service.rs
@@ -0,0 +1,196 @@
+// 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.
+
+//! Provides a binder service for key generation & verification for CompOs. We assume we have
+//! access to Keystore in the VM, but not persistent storage; instead the host stores the key
+//! on our behalf via this service.
+
+use android_hardware_security_keymint::aidl::android::hardware::security::keymint::{
+ Algorithm::Algorithm, Digest::Digest, KeyParameter::KeyParameter,
+ KeyParameterValue::KeyParameterValue, KeyPurpose::KeyPurpose, PaddingMode::PaddingMode,
+ SecurityLevel::SecurityLevel, Tag::Tag,
+};
+use android_system_keystore2::aidl::android::system::keystore2::{
+ Domain::Domain, IKeystoreSecurityLevel::IKeystoreSecurityLevel,
+ IKeystoreService::IKeystoreService, KeyDescriptor::KeyDescriptor,
+};
+use anyhow::{anyhow, Context, Result};
+use compos_aidl_interface::aidl::com::android::compos::{
+ CompOsKeyData::CompOsKeyData,
+ ICompOsKeyService::{BnCompOsKeyService, ICompOsKeyService},
+};
+use compos_aidl_interface::binder::{
+ self, add_service, get_interface, BinderFeatures, ExceptionCode, Interface, ProcessState,
+ Status, Strong,
+};
+use log::{info, warn, Level};
+use ring::rand::{SecureRandom, SystemRandom};
+use ring::signature;
+use scopeguard::ScopeGuard;
+use std::ffi::CString;
+use std::sync::Mutex;
+
+const LOG_TAG: &str = "CompOsKeyService";
+const OUR_SERVICE_NAME: &str = "android.system.composkeyservice";
+
+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 =
+ KeyParameter { tag: Tag::ALGORITHM, value: KeyParameterValue::Algorithm(Algorithm::RSA) };
+const PADDING: KeyParameter = KeyParameter {
+ tag: Tag::PADDING,
+ value: KeyParameterValue::PaddingMode(PaddingMode::RSA_PKCS1_1_5_SIGN),
+};
+const DIGEST: KeyParameter =
+ KeyParameter { tag: Tag::DIGEST, value: KeyParameterValue::Digest(Digest::SHA_2_256) };
+const KEY_SIZE: KeyParameter =
+ KeyParameter { tag: Tag::KEY_SIZE, value: KeyParameterValue::Integer(2048) };
+const EXPONENT: KeyParameter =
+ KeyParameter { tag: Tag::RSA_PUBLIC_EXPONENT, value: KeyParameterValue::LongInteger(65537) };
+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 };
+
+struct CompOsKeyService {
+ random: SystemRandom,
+ state: Mutex<State>,
+}
+
+struct State {
+ security_level: Strong<dyn IKeystoreSecurityLevel>,
+}
+
+impl Interface for CompOsKeyService {}
+
+impl ICompOsKeyService for CompOsKeyService {
+ fn generateSigningKey(&self) -> binder::Result<CompOsKeyData> {
+ self.do_generate()
+ .map_err(|e| new_binder_exception(ExceptionCode::ILLEGAL_STATE, e.to_string()))
+ }
+
+ fn verifySigningKey(&self, key_blob: &[u8], public_key: &[u8]) -> binder::Result<bool> {
+ Ok(if let Err(e) = self.do_verify(key_blob, public_key) {
+ warn!("Signing key verification failed: {}", e.to_string());
+ false
+ } else {
+ true
+ })
+ }
+}
+
+/// Constructs a new Binder error `Status` with the given `ExceptionCode` and message.
+fn new_binder_exception<T: AsRef<str>>(exception: ExceptionCode, message: T) -> Status {
+ Status::new_exception(exception, CString::new(message.as_ref()).ok().as_deref())
+}
+
+impl CompOsKeyService {
+ fn new(keystore_service: &Strong<dyn IKeystoreService>) -> Self {
+ Self {
+ random: SystemRandom::new(),
+ state: Mutex::new(State {
+ security_level: keystore_service
+ .getSecurityLevel(SecurityLevel::TRUSTED_ENVIRONMENT)
+ .unwrap(),
+ }),
+ }
+ }
+
+ fn security_level(&self) -> Strong<dyn IKeystoreSecurityLevel> {
+ // We need the Mutex because Strong<_> isn't sync. But we don't need to keep it locked
+ // to make the call, once we've cloned the pointer.
+ self.state.lock().unwrap().security_level.clone()
+ }
+
+ fn do_generate(&self) -> Result<CompOsKeyData> {
+ let key_parameters =
+ [PURPOSE_SIGN, ALGORITHM, PADDING, DIGEST, KEY_SIZE, EXPONENT, NO_AUTH_REQUIRED];
+ let attestation_key = None;
+ let flags = 0;
+ let entropy = [];
+
+ let key_metadata = self
+ .security_level()
+ .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) {
+ Ok(CompOsKeyData { certificate, keyBlob: blob })
+ } else {
+ Err(anyhow!("Missing cert or blob"))
+ }
+ }
+
+ fn do_verify(&self, key_blob: &[u8], public_key: &[u8]) -> Result<()> {
+ let mut data = [0u8; 32];
+ self.random.fill(&mut data).context("No random data")?;
+
+ let signature = self.sign(key_blob, &data)?;
+
+ let public_key =
+ signature::UnparsedPublicKey::new(&signature::RSA_PKCS1_2048_8192_SHA256, public_key);
+ public_key.verify(&data, &signature).context("Signature verification failed")?;
+
+ Ok(())
+ }
+
+ fn sign(&self, key_blob: &[u8], data: &[u8]) -> Result<Vec<u8>> {
+ let key_descriptor = KeyDescriptor { blob: Some(key_blob.to_vec()), ..KEY_DESCRIPTOR };
+ let operation_parameters = [PURPOSE_SIGN, ALGORITHM, PADDING, DIGEST];
+ let forced = false;
+
+ let response = self
+ .security_level()
+ .createOperation(&key_descriptor, &operation_parameters, forced)
+ .context("Creating key failed")?;
+ let operation = scopeguard::guard(
+ response.iOperation.ok_or_else(|| anyhow!("No operation created"))?,
+ |op| op.abort().unwrap_or_default(),
+ );
+
+ if response.operationChallenge.is_some() {
+ return Err(anyhow!("Key requires user authorization"));
+ }
+
+ let signature = operation.finish(Some(&data), None).context("Signing failed")?;
+ // Operation has finished, we're no longer responsible for aborting it
+ ScopeGuard::into_inner(operation);
+
+ signature.ok_or_else(|| anyhow!("No signature returned"))
+ }
+}
+
+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 keystore_service = get_interface::<dyn IKeystoreService>(KEYSTORE_SERVICE_NAME)
+ .context("No Keystore service")?;
+ let service = CompOsKeyService::new(&keystore_service);
+ 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(())
+}