Rate-limit per-UID hardware keygen and harden importKey eviction
Sliding window limits each UID to 2 hardware generateKey calls per 30s burst window with max 2 concurrent. Overflow falls back to software cert generation. importKey post-hook retains patched chains instead of full eviction, preventing detectors from using generate-then-import to bypass attestation patching. getKeyEntry serves retained chains for imported keys that overwrote attested aliases.
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Enginex0
+9
-2
@@ -220,8 +220,15 @@ object Keystore2Interceptor : AbstractKeystoreInterceptor() {
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?.let { it.keyParameter.value.origin }
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if (origin == KeyOrigin.IMPORTED || origin == KeyOrigin.SECURELY_IMPORTED) {
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SystemLogger.info("[TX_ID: $txId] Skip patching for imported keys.")
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return TransactionResult.SkipTransaction
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val keyId = KeyIdentifier(callingUid, keyDescriptor.alias)
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val retainedChain = KeyMintSecurityLevelInterceptor.getPatchedChain(keyId)
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if (retainedChain == null) {
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SystemLogger.info("[TX_ID: $txId] Skip patching for imported key (no prior attestation).")
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return TransactionResult.SkipTransaction
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}
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SystemLogger.info("[TX_ID: $txId] Imported key overwrote attested alias, serving retained chain for $keyId")
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CertificateHelper.updateCertificateChain(response.metadata, retainedChain).getOrThrow()
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return InterceptorUtils.createTypedObjectReply(response)
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}
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if (originalChain == null || originalChain.size < 2) {
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+104
-45
@@ -16,6 +16,7 @@ import java.security.cert.Certificate
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import java.security.cert.CertificateFactory
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import java.security.spec.PKCS8EncodedKeySpec
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import java.util.concurrent.ConcurrentHashMap
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import java.util.concurrent.atomic.AtomicInteger
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import org.matrix.TEESimulator.attestation.AttestationPatcher
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import org.matrix.TEESimulator.attestation.KeyMintAttestation
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import org.matrix.TEESimulator.config.ConfigurationManager
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@@ -52,7 +53,7 @@ class KeyMintSecurityLevelInterceptor(
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GENERATE_KEY_TRANSACTION -> {
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logTransaction(txId, transactionNames[code]!!, callingUid, callingPid)
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if (!shouldSkip) return handleGenerateKey(callingUid, data)
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if (!shouldSkip) return handleGenerateKey(txId, callingUid, data)
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}
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CREATE_OPERATION_TRANSACTION -> {
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logTransaction(txId, transactionNames[code]!!, callingUid, callingPid)
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@@ -93,6 +94,11 @@ class KeyMintSecurityLevelInterceptor(
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reply: Parcel?,
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resultCode: Int,
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): TransactionResult {
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if (code == GENERATE_KEY_TRANSACTION && hardwareKeygenTxIds.remove(txId)) {
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val remaining = hardwareKeygenCount(callingUid).decrementAndGet()
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SystemLogger.info("[TX_ID: $txId] PERMIT_RELEASED uid=$callingUid concurrent_remaining=$remaining result=${if (resultCode == 0) "OK" else "ERROR($resultCode)"}")
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}
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// We only care about successful transactions.
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if (resultCode != 0 || reply == null || InterceptorUtils.hasException(reply))
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return TransactionResult.SkipTransaction
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@@ -104,7 +110,14 @@ class KeyMintSecurityLevelInterceptor(
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val keyDescriptor =
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data.readTypedObject(KeyDescriptor.CREATOR)
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?: return TransactionResult.SkipTransaction
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cleanupKeyData(KeyIdentifier(callingUid, keyDescriptor.alias))
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// Evict generated key data but retain patched chains so detectors
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// can't use importKey to force unpatched getKeyEntry responses.
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val keyId = KeyIdentifier(callingUid, keyDescriptor.alias)
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if (generatedKeys.remove(keyId) != null) {
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SystemLogger.debug("Remove generated key on importKey $keyId")
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GeneratedKeyPersistence.delete(keyId)
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}
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attestationKeys.remove(keyId)
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} else if (code == CREATE_OPERATION_TRANSACTION) {
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logTransaction(txId, "post-${transactionNames[code]!!}", callingUid, callingPid)
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@@ -212,18 +225,17 @@ class KeyMintSecurityLevelInterceptor(
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return InterceptorUtils.createTypedObjectReply(response)
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}
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private fun handleGenerateKey(callingUid: Int, data: Parcel): TransactionResult {
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private fun handleGenerateKey(txId: Long, callingUid: Int, data: Parcel): TransactionResult {
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if (data.dataSize() > MAX_ALIAS_LENGTH) {
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SystemLogger.warning("Skipping oversized transaction: ${data.dataSize()} bytes")
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return TransactionResult.ContinueAndSkipPost
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}
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return runCatching {
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data.enforceInterface(IKeystoreSecurityLevel.DESCRIPTOR)
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val keyDescriptor = data.readTypedObject(KeyDescriptor.CREATOR)!!
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val attestationKey = data.readTypedObject(KeyDescriptor.CREATOR)
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// Reject oversized aliases to prevent binder buffer exhaustion (Issue #109)
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if (keyDescriptor.alias.length > MAX_ALIAS_LENGTH) {
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SystemLogger.warning("Rejecting oversized alias: ${keyDescriptor.alias.length} bytes (max: $MAX_ALIAS_LENGTH)")
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return TransactionResult.ContinueAndSkipPost
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}
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SystemLogger.debug(
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"Handling generateKey ${keyDescriptor.alias}, attestKey=${attestationKey?.alias}"
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)
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@@ -241,43 +253,26 @@ class KeyMintSecurityLevelInterceptor(
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isAttestationKey(KeyIdentifier(callingUid, attestationKey.alias)))
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if (needsSoftwareGeneration) {
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keyDescriptor.nspace = secureRandom.nextLong()
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SystemLogger.info(
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"Generating software key for ${keyDescriptor.alias}[${keyDescriptor.nspace}]."
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)
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val keyData =
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CertificateGenerator.generateAttestedKeyPair(
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callingUid,
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keyDescriptor.alias,
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attestationKey?.alias,
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parsedParams,
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securityLevel,
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) ?: throw Exception("CertificateGenerator failed to create key pair.")
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cleanupKeyData(keyId)
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val response =
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buildKeyEntryResponse(keyData.second, parsedParams, keyDescriptor)
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generatedKeys[keyId] =
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GeneratedKeyInfo(keyData.first, keyDescriptor.nspace, response)
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if (isAttestKeyRequest) attestationKeys.add(keyId)
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GeneratedKeyPersistence.save(
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keyId = keyId,
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keyPair = keyData.first,
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nspace = keyDescriptor.nspace,
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securityLevel = securityLevel,
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certChain = keyData.second.toList(),
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algorithm = parsedParams.algorithm,
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keySize = parsedParams.keySize,
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ecCurve = parsedParams.ecCurve,
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purposes = parsedParams.purpose,
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digests = parsedParams.digest,
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isAttestationKey = isAttestKeyRequest,
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)
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return InterceptorUtils.createTypedObjectReply(response.metadata)
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return doSoftwareKeyGen(callingUid, keyDescriptor, attestationKey, parsedParams, keyId, isAttestKeyRequest)
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} else if (parsedParams.attestationChallenge != null) {
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val windowUsed = hardwareKeygenWindowCount(callingUid)
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val concurrentUsed = hardwareKeygenCount(callingUid).get()
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// Sliding window rate limit
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if (windowUsed >= MAX_HW_KEYGEN_PER_WINDOW) {
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SystemLogger.info("[TX_ID: $txId] RATE_LIMITED uid=$callingUid window=$windowUsed/$MAX_HW_KEYGEN_PER_WINDOW concurrent=$concurrentUsed → software fallback")
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return doSoftwareKeyGen(callingUid, keyDescriptor, attestationKey, parsedParams, keyId, isAttestKeyRequest)
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}
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// Concurrent cap
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if (hardwareKeygenCount(callingUid).incrementAndGet() > MAX_CONCURRENT_HW_KEYGEN_PER_UID) {
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hardwareKeygenCount(callingUid).decrementAndGet()
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SystemLogger.info("[TX_ID: $txId] CONCURRENT_LIMITED uid=$callingUid window=$windowUsed/$MAX_HW_KEYGEN_PER_WINDOW concurrent=${concurrentUsed + 1}/$MAX_CONCURRENT_HW_KEYGEN_PER_UID → software fallback")
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return doSoftwareKeyGen(callingUid, keyDescriptor, attestationKey, parsedParams, keyId, isAttestKeyRequest)
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}
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// Both checks passed — commit the window permit and forward to hardware TEE
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recordHardwareKeygen(callingUid)
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hardwareKeygenTxIds.add(txId)
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SystemLogger.info("[TX_ID: $txId] HARDWARE_KEYGEN uid=$callingUid window=${windowUsed + 1}/$MAX_HW_KEYGEN_PER_WINDOW concurrent=${concurrentUsed + 1}/$MAX_CONCURRENT_HW_KEYGEN_PER_UID → forwarding to TEE")
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return TransactionResult.Continue
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}
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@@ -290,6 +285,43 @@ class KeyMintSecurityLevelInterceptor(
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}
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}
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private fun doSoftwareKeyGen(
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callingUid: Int,
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keyDescriptor: KeyDescriptor,
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attestationKey: KeyDescriptor?,
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parsedParams: KeyMintAttestation,
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keyId: KeyIdentifier,
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isAttestKeyRequest: Boolean,
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): TransactionResult {
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keyDescriptor.nspace = secureRandom.nextLong()
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SystemLogger.info("Generating software key for ${keyDescriptor.alias}[${keyDescriptor.nspace}].")
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val keyData = CertificateGenerator.generateAttestedKeyPair(
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callingUid, keyDescriptor.alias, attestationKey?.alias, parsedParams, securityLevel,
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) ?: throw Exception("CertificateGenerator failed to create key pair.")
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cleanupKeyData(keyId)
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val response = buildKeyEntryResponse(keyData.second, parsedParams, keyDescriptor)
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generatedKeys[keyId] = GeneratedKeyInfo(keyData.first, keyDescriptor.nspace, response)
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if (isAttestKeyRequest) attestationKeys.add(keyId)
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GeneratedKeyPersistence.save(
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keyId = keyId,
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keyPair = keyData.first,
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nspace = keyDescriptor.nspace,
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securityLevel = securityLevel,
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certChain = keyData.second.toList(),
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algorithm = parsedParams.algorithm,
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keySize = parsedParams.keySize,
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ecCurve = parsedParams.ecCurve,
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purposes = parsedParams.purpose,
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digests = parsedParams.digest,
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isAttestationKey = isAttestKeyRequest,
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)
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return InterceptorUtils.createTypedObjectReply(response.metadata)
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}
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private fun buildKeyEntryResponse(
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chain: List<Certificate>,
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params: KeyMintAttestation,
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@@ -395,6 +427,33 @@ class KeyMintSecurityLevelInterceptor(
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// Maximum alias length to prevent binder buffer exhaustion (Issue #109)
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// Binder buffer is ~1MB; 256KB provides 4x safety margin for transaction overhead
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private const val MAX_ALIAS_LENGTH = 256 * 1024
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private const val MAX_CONCURRENT_HW_KEYGEN_PER_UID = 2
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// Sliding window: max hardware keygen permits per UID within the burst window
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private const val MAX_HW_KEYGEN_PER_WINDOW = 2
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private const val BURST_WINDOW_MS = 30_000L
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private val uidHardwareKeygenCount = ConcurrentHashMap<Int, AtomicInteger>()
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private val hardwareKeygenTxIds = ConcurrentHashMap.newKeySet<Long>()
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private val uidKeygenTimestamps = ConcurrentHashMap<Int, MutableList<Long>>()
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private fun hardwareKeygenCount(uid: Int): AtomicInteger =
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uidHardwareKeygenCount.computeIfAbsent(uid) { AtomicInteger(0) }
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private fun hardwareKeygenWindowCount(uid: Int): Int {
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val now = System.currentTimeMillis()
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val timestamps = uidKeygenTimestamps.computeIfAbsent(uid) { mutableListOf() }
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synchronized(timestamps) {
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timestamps.removeAll { now - it > BURST_WINDOW_MS }
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return timestamps.size
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}
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}
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private fun recordHardwareKeygen(uid: Int) {
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val timestamps = uidKeygenTimestamps.computeIfAbsent(uid) { mutableListOf() }
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synchronized(timestamps) {
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timestamps.add(System.currentTimeMillis())
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}
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}
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private val GENERATE_KEY_TRANSACTION =
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InterceptorUtils.getTransactCode(IKeystoreSecurityLevel.Stub::class.java, "generateKey")
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