Support key enumeration via listEntries interception (#84)

Previously, generated keys were functional but invisible to enumeration APIs like `KeyStore.aliases()`. Because these keys reside solely in the simulator's memory, the standard database query performed by the system Keystore does not return them.

This commit intercepts `listEntries` and `listEntriesBatched` to inject these generated keys into the results.

Key implementation details:
- ListEntriesHandler: Encapsulates the logic to merge hardware-backed keys with software-backed keys.
- Ordering: Uses a `TreeMap` to ensure merged results are lexicographically sorted, mimicking AOSP behavior.
- Binder Safety: Implements `estimateSafeAmountToReturn` to calculate the response size. The handler truncates the result list if it exceeds the binder transaction limit (~350KB) as done in AOSP.
- Pagination: Respects the `startPastAlias` parameter to support batched listing.

Co-authored-by: JingMatrix <jingmatrix@gmail.com>

app/src/main/java/org/matrix/TEESimulator/interception/keystore/InterceptorUtils.kt

@@ -65,6 +65,19 @@ object InterceptorUtils {
         return BinderInterceptor.TransactionResult.OverrideReply(parcel)
     }
 
+    /** Creates an `OverrideReply` parcel containing a typed array. */
+    fun <T : Parcelable> createTypedArrayReply(
+        array: Array<T>,
+        flags: Int = 0,
+    ): BinderInterceptor.TransactionResult.OverrideReply {
+        val parcel =
+            Parcel.obtain().apply {
+                writeNoException()
+                writeTypedArray(array, flags)
+            }
+        return BinderInterceptor.TransactionResult.OverrideReply(parcel)
+    }
+
     /** Creates an `OverrideReply` parcel containing a Parcelable object. */
     fun <T : Parcelable?> createTypedObjectReply(
         obj: T,

app/src/main/java/org/matrix/TEESimulator/interception/keystore/Keystore2Interceptor.kt

@@ -4,6 +4,7 @@ import android.annotation.SuppressLint
 import android.hardware.security.keymint.KeyOrigin
 import android.hardware.security.keymint.SecurityLevel
 import android.hardware.security.keymint.Tag
+import android.os.Build
 import android.os.IBinder
 import android.os.Parcel
 import android.system.keystore2.IKeystoreService
@@ -33,6 +34,11 @@ object Keystore2Interceptor : AbstractKeystoreInterceptor() {
         InterceptorUtils.getTransactCode(IKeystoreService.Stub::class.java, "deleteKey")
     private val UPDATE_SUBCOMPONENT_TRANSACTION =
         InterceptorUtils.getTransactCode(IKeystoreService.Stub::class.java, "updateSubcomponent")
+    private val LIST_ENTRIES_TRANSACTION =
+        InterceptorUtils.getTransactCode(IKeystoreService.Stub::class.java, "listEntries")
+    private val LIST_ENTRIES_BATCHED_TRANSACTION =
+        InterceptorUtils.getTransactCode(IKeystoreService.Stub::class.java, "listEntriesBatched")
+            .takeIf { Build.VERSION.SDK_INT >= 34 }
 
     private val transactionNames: Map<Int, String> by lazy {
         IKeystoreService.Stub::class
@@ -91,7 +97,28 @@ object Keystore2Interceptor : AbstractKeystoreInterceptor() {
         callingPid: Int,
         data: Parcel,
     ): TransactionResult {
-        if (
+        if (code == LIST_ENTRIES_TRANSACTION || code == LIST_ENTRIES_BATCHED_TRANSACTION) {
+            logTransaction(txId, transactionNames[code]!!, callingUid, callingPid)
+
+            if (ConfigurationManager.shouldSkipUid(callingUid))
+                return TransactionResult.ContinueAndSkipPost
+
+            return runCatching {
+                    val isBatchMode = code == LIST_ENTRIES_BATCHED_TRANSACTION
+                    if (ListEntriesHandler.cacheParameters(txId, data, isBatchMode)) {
+                        TransactionResult.Continue
+                    } else {
+                        TransactionResult.ContinueAndSkipPost
+                    }
+                }
+                .getOrElse {
+                    SystemLogger.error(
+                        "[TX_ID: $txId] Failed to parse parameters for ${transactionNames[code]!!}",
+                        it,
+                    )
+                    TransactionResult.ContinueAndSkipPost
+                }
+        } else if (
             code == GET_KEY_ENTRY_TRANSACTION ||
                 code == DELETE_KEY_TRANSACTION ||
                 code == UPDATE_SUBCOMPONENT_TRANSACTION
@@ -163,7 +190,22 @@ object Keystore2Interceptor : AbstractKeystoreInterceptor() {
         if (target != keystoreService || reply == null || InterceptorUtils.hasException(reply))
             return TransactionResult.SkipTransaction
 
-        if (code == GET_KEY_ENTRY_TRANSACTION) {
+        if (code == LIST_ENTRIES_TRANSACTION || code == LIST_ENTRIES_BATCHED_TRANSACTION) {
+            logTransaction(txId, "post-${transactionNames[code]!!}", callingUid, callingPid)
+
+            return runCatching {
+                    val updatedKeyDescriptors =
+                        ListEntriesHandler.injectGeneratedKeys(txId, callingUid, reply)
+                    InterceptorUtils.createTypedArrayReply(updatedKeyDescriptors)
+                }
+                .getOrElse {
+                    SystemLogger.error(
+                        "[TX_ID: $txId] Failed to update the result of ${transactionNames[code]!!}.",
+                        it,
+                    )
+                    TransactionResult.SkipTransaction
+                }
+        } else if (code == GET_KEY_ENTRY_TRANSACTION) {
             logTransaction(txId, "post-${transactionNames[code]!!}", callingUid, callingPid)
 
             data.enforceInterface(IKeystoreService.DESCRIPTOR)

app/src/main/java/org/matrix/TEESimulator/interception/keystore/ListEntriesHandler.kt

@@ -0,0 +1,142 @@
+package org.matrix.TEESimulator.interception.keystore
+
+import android.os.Parcel
+import android.system.keystore2.Domain
+import android.system.keystore2.IKeystoreService
+import android.system.keystore2.KeyDescriptor
+import java.util.TreeMap
+import java.util.concurrent.ConcurrentHashMap
+import org.matrix.TEESimulator.interception.keystore.shim.KeyMintSecurityLevelInterceptor
+import org.matrix.TEESimulator.logging.SystemLogger
+
+/**
+ * Handler to intercept listEntries and listEntriesBatched transactions.
+ *
+ * References for all mentioned functions in AOSP:
+ * https://cs.android.com/android/platform/superproject/main/+/main:system/security/keystore2/src/database.rs
+ * https://cs.android.com/android/platform/superproject/main/+/main:system/security/keystore2/src/service.rs
+ * https://cs.android.com/android/platform/superproject/main/+/main:system/security/keystore2/src/utils.rs
+ */
+object ListEntriesHandler {
+
+    // Estimate for maximum size of a Binder response in bytes.
+    private const val RESPONSE_SIZE_LIMIT = 358400
+
+    // Parameters of AOSP function `list_key_entries` in utils.rs.
+    private data class ListEntriesParams(
+        val domain: Int,
+        val namespace: Long,
+        val startPastAlias: String?,
+    )
+
+    private val pendingParams = ConcurrentHashMap<Long, ListEntriesParams>()
+
+    // Based on AOSP function `estimate_safe_amount_to_return` in utils.rs.
+    private fun estimateSafeAmountToReturn(
+        keyDescriptors: Array<KeyDescriptor>,
+        responseSizeLimit: Int,
+    ): Int {
+        var itemsToReturn = 0
+        var returnedBytes = 0
+
+        for (kd in keyDescriptors) {
+            // 4 bytes for the Domain enum
+            // 8 bytes for the Namespace long
+            returnedBytes += 4 + 8
+
+            kd.alias?.let { returnedBytes += 4 + it.toByteArray(Charsets.UTF_8).size }
+            kd.blob?.let { returnedBytes += 4 + it.size }
+
+            if (returnedBytes > responseSizeLimit) {
+                SystemLogger.warning(
+                    "Key descriptors list (${keyDescriptors.size} items) may exceed binder size limit, returning $itemsToReturn items with estimated size: $returnedBytes bytes."
+                )
+                break
+            }
+            itemsToReturn++
+        }
+
+        return itemsToReturn
+    }
+
+    // Parse and store parameters for later use (in post-transaction).
+    fun cacheParameters(txId: Long, data: Parcel, isBatchMode: Boolean): Boolean {
+        data.enforceInterface(IKeystoreService.DESCRIPTOR)
+
+        val domain = data.readInt()
+        val namespace = data.readLong()
+        val startPastAlias = if (isBatchMode) data.readString() else null
+
+        // List entries is only supported for Domain::APP and Domain::SELINUX.
+        // See AOSP function `get_key_descriptor_for_lookup` in service.rs.
+        // Note that all generated keys belong to Domain::APP.
+        if (domain == Domain.APP) {
+            pendingParams[txId] = ListEntriesParams(domain, namespace, startPastAlias)
+            SystemLogger.debug("[TX_ID: $txId] Cached ${pendingParams[txId]}.")
+            return true
+        }
+
+        return false
+    }
+
+    // Merge software-backed keys with hardware-backed keys in the reply parcel.
+    fun injectGeneratedKeys(txId: Long, callingUid: Int, reply: Parcel): Array<KeyDescriptor> {
+        val params =
+            pendingParams.remove(txId)
+                ?: throw IllegalStateException("No params found for listing entries")
+
+        // By default we use the calling uid as namespace if domain is Domain::APP.
+        // The namespace parameter is thus ignored for non-privileged applications.
+        // See AOSP function `get_key_descriptor_for_lookup` in service.rs.
+        val keysToInject =
+            extractGeneratedKeyDescriptors(callingUid, callingUid.toLong(), params.startPastAlias)
+        val originalList = reply.createTypedArray(KeyDescriptor.CREATOR)!!
+        val mergedArray = mergeKeyDescriptors(originalList, keysToInject)
+
+        // Limit response size to avoid binder buffer overflow.
+        // See AOSP function `list_key_entries` in utils.rs.
+        val safeAmountToReturn = estimateSafeAmountToReturn(mergedArray, RESPONSE_SIZE_LIMIT)
+
+        return if (safeAmountToReturn < mergedArray.size) {
+            SystemLogger.debug(
+                "[TX_ID: $txId] Listing entries are truncated [${mergedArray.size} -> $safeAmountToReturn] to avoid transaction overflow."
+            )
+            mergedArray.copyOfRange(0, safeAmountToReturn)
+        } else {
+            SystemLogger.debug(
+                "[TX_ID: $txId] Listing entries returns ${mergedArray.size} [injected: ${keysToInject.size}] keys."
+            )
+            mergedArray
+        }
+    }
+
+    // Merge hardware and software key descriptors into a single sorted array.
+    private fun mergeKeyDescriptors(
+        hardwareKeys: Array<KeyDescriptor>,
+        keysToInject: List<KeyDescriptor>,
+    ): Array<KeyDescriptor> {
+        // Uses TreeMap to ensure alphabetical ordering and uniqueness (prefer injected keys).
+        val combinedMap = TreeMap<String, KeyDescriptor>()
+        hardwareKeys.forEach { key -> key.alias?.let { combinedMap[it] = key } }
+        keysToInject.forEach { key -> key.alias?.let { combinedMap[it] = key } }
+        return combinedMap.values.toTypedArray()
+    }
+
+    // Based on AOSP function `list_past_alias` in database.rs
+    private fun extractGeneratedKeyDescriptors(
+        uid: Int,
+        namespace: Long,
+        startPastAlias: String?,
+    ): List<KeyDescriptor> {
+        return KeyMintSecurityLevelInterceptor.generatedKeys.keys
+            .filter { it.uid == uid && (startPastAlias == null || it.alias < startPastAlias) }
+            .map { keyId ->
+                KeyDescriptor().apply {
+                    this.domain = Domain.APP
+                    this.nspace = namespace
+                    this.alias = keyId.alias
+                    this.blob = null
+                }
+            }
+    }
+}