[MTE] Parse MTE sysprop in system_server

The system server inherits the ELF note from the Zygote, but should also
be able to be overwritten by the system property. This needs to be
manually parsed.

Bug: 172365548
Test: 'adb shell setprop arm64.memtag.process.system_server 123' \
Test: ... kill the system_server, and and look in logcat for
Test  ... "Unknown memory tag level for the system server".
Test: 'adb shell setprop arm64.memtag.process.system_server sync' \
Test: ... kill the system_server, and look in logcat for
Test: ... "SetHeapTaggingLevel: tag level set to 3".

Change-Id: Icda4ff141646086ae85d751b8af9b1fe94bfd7b5

1 files changed, 32 insertions, 0 deletions

diff --git a/core/jni/com_android_internal_os_Zygote.cpp b/core/jni/com_android_internal_os_Zygote.cpp
index d7001d8d36ea..903ecaef4938 100644
--- a/core/jni/com_android_internal_os_Zygote.cpp
+++ b/core/jni/com_android_internal_os_Zygote.cpp
@@ -2526,6 +2526,36 @@ static jboolean com_android_internal_os_Zygote_nativeSupportsTaggedPointers(JNIE
 #endif
 }
 
+static jint com_android_internal_os_Zygote_nativeCurrentTaggingLevel(JNIEnv* env, jclass) {
+#if defined(__aarch64__)
+  int level = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+  if (level < 0) {
+    ALOGE("Failed to get memory tag level: %s", strerror(errno));
+    return 0;
+  } else if (!(level & PR_TAGGED_ADDR_ENABLE)) {
+    return 0;
+  }
+  // TBI is only possible on non-MTE hardware.
+  if (!mte_supported()) {
+    return MEMORY_TAG_LEVEL_TBI;
+  }
+
+  switch (level & PR_MTE_TCF_MASK) {
+    case PR_MTE_TCF_NONE:
+      return 0;
+    case PR_MTE_TCF_SYNC:
+      return MEMORY_TAG_LEVEL_SYNC;
+    case PR_MTE_TCF_ASYNC:
+      return MEMORY_TAG_LEVEL_ASYNC;
+    default:
+      ALOGE("Unknown memory tagging level: %i", level);
+      return 0;
+  }
+#else // defined(__aarch64__)
+  return 0;
+#endif // defined(__aarch64__)
+}
+
 static const JNINativeMethod gMethods[] = {
         {"nativeForkAndSpecialize",
          "(II[II[[IILjava/lang/String;Ljava/lang/String;[I[IZLjava/lang/String;Ljava/lang/"
@@ -2565,6 +2595,8 @@ static const JNINativeMethod gMethods[] = {
          (void*)com_android_internal_os_Zygote_nativeSupportsMemoryTagging},
         {"nativeSupportsTaggedPointers", "()Z",
          (void*)com_android_internal_os_Zygote_nativeSupportsTaggedPointers},
+        {"nativeCurrentTaggingLevel", "()I",
+         (void*)com_android_internal_os_Zygote_nativeCurrentTaggingLevel},
 };
 
 int register_com_android_internal_os_Zygote(JNIEnv* env) {