Don't ask libc for PT feature w/o kernel support.

Check that the kernel supports the Tagged Pointers feature before asking
libc to disable/enable pointer tagging.

Bug: 153114333
Test: Build coral, note no messages from SetHeapTaggingLevel.
Test: atest CtsTaggingHostTestCases

Change-Id: Id5fbd731aa70f7b0a75525387479f6123628a012
Merged-In: Id5fbd731aa70f7b0a75525387479f6123628a012

4 files changed, 30 insertions, 8 deletions

diff --git a/core/java/com/android/internal/os/Zygote.java b/core/java/com/android/internal/os/Zygote.java
index ff03f1a1a2ab..34f4957735fe 100644
--- a/core/java/com/android/internal/os/Zygote.java
+++ b/core/java/com/android/internal/os/Zygote.java
@@ -1060,4 +1060,11 @@ public final class Zygote {
      */
     @FastNative
     public static native int nativeParseSigChld(byte[] in, int length, int[] out);
+
+    /**
+     * Returns whether the kernel supports tagged pointers. Present in the
+     * Android Common Kernel from 4.14 and up. By default, you should prefer
+     * fully-feature Memory Tagging, rather than the static Tagged Pointers.
+     */
+    public static native boolean nativeSupportsTaggedPointers();
 }
diff --git a/core/java/com/android/internal/os/ZygoteInit.java b/core/java/com/android/internal/os/ZygoteInit.java
index ec1f516df5f3..c2b13c971020 100644
--- a/core/java/com/android/internal/os/ZygoteInit.java
+++ b/core/java/com/android/internal/os/ZygoteInit.java
@@ -757,9 +757,11 @@ public class ZygoteInit {
             Zygote.applyDebuggerSystemProperty(parsedArgs);
             Zygote.applyInvokeWithSystemProperty(parsedArgs);
 
-            /* Enable pointer tagging in the system server unconditionally. Hardware support for
-             * this is present in all ARMv8 CPUs; this flag has no effect on other platforms. */
-            parsedArgs.mRuntimeFlags |= Zygote.MEMORY_TAG_LEVEL_TBI;
+            if (Zygote.nativeSupportsTaggedPointers()) {
+                /* Enable pointer tagging in the system server. Hardware support for this is present
+                 * in all ARMv8 CPUs. */
+                parsedArgs.mRuntimeFlags |= Zygote.MEMORY_TAG_LEVEL_TBI;
+            }
 
             /* Enable gwp-asan on the system server with a small probability. This is the same
              * policy as applied to native processes and system apps. */
diff --git a/core/jni/com_android_internal_os_Zygote.cpp b/core/jni/com_android_internal_os_Zygote.cpp
index ea3c0fa9fc3c..38b88ec4af45 100644
--- a/core/jni/com_android_internal_os_Zygote.cpp
+++ b/core/jni/com_android_internal_os_Zygote.cpp
@@ -2405,6 +2405,15 @@ static jint com_android_internal_os_Zygote_nativeParseSigChld(JNIEnv* env, jclas
     return -1;
 }
 
+static jboolean com_android_internal_os_Zygote_nativeSupportsTaggedPointers(JNIEnv* env, jclass) {
+#ifdef __aarch64__
+  int res = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+  return res >= 0 && res & PR_TAGGED_ADDR_ENABLE;
+#else
+  return false;
+#endif
+}
+
 static const JNINativeMethod gMethods[] = {
         {"nativeForkAndSpecialize",
          "(II[II[[IILjava/lang/String;Ljava/lang/String;[I[IZLjava/lang/String;Ljava/lang/"
@@ -2440,6 +2449,8 @@ static const JNINativeMethod gMethods[] = {
          (void*)com_android_internal_os_Zygote_nativeBoostUsapPriority},
         {"nativeParseSigChld", "([BI[I)I",
          (void*)com_android_internal_os_Zygote_nativeParseSigChld},
+        {"nativeSupportsTaggedPointers", "()Z",
+         (void*)com_android_internal_os_Zygote_nativeSupportsTaggedPointers},
 };
 
 int register_com_android_internal_os_Zygote(JNIEnv* env) {
diff --git a/services/core/java/com/android/server/am/ProcessList.java b/services/core/java/com/android/server/am/ProcessList.java
index 595275d20154..cb6990a82f00 100644
--- a/services/core/java/com/android/server/am/ProcessList.java
+++ b/services/core/java/com/android/server/am/ProcessList.java
@@ -1846,11 +1846,13 @@ public final class ProcessList {
                 runtimeFlags |= Zygote.USE_APP_IMAGE_STARTUP_CACHE;
             }
 
-            // Enable heap pointer tagging, unless disabled by the app manifest, target sdk level,
-            // or the compat feature.
-            if (app.info.allowsNativeHeapPointerTagging()
-                    && mPlatformCompat.isChangeEnabled(NATIVE_HEAP_POINTER_TAGGING, app.info)) {
-                runtimeFlags |= Zygote.MEMORY_TAG_LEVEL_TBI;
+            if (Zygote.nativeSupportsTaggedPointers()) {
+                // Enable heap pointer tagging if supported by the kernel, unless disabled by the
+                // app manifest, target sdk level, or compat feature.
+                if (app.info.allowsNativeHeapPointerTagging()
+                        && mPlatformCompat.isChangeEnabled(NATIVE_HEAP_POINTER_TAGGING, app.info)) {
+                    runtimeFlags |= Zygote.MEMORY_TAG_LEVEL_TBI;
+                }
             }
 
             runtimeFlags |= decideGwpAsanLevel(app);