LockAgent: Add ability to generate a native crash

Use the crasher to create a tombstone with the violation as the abort
message.

Test: m
Test: manual
Change-Id: I8c5041a4fbffedb11b6b9c564ab1e214551896bf

tools/lock_agent/Android.bp

@@ -15,6 +15,8 @@ cc_library {
     include_dirs: [
         // NDK headers aren't available in platform NDK builds.
         "libnativehelper/include_jni",
+        // Use ScopedUtfChars.
+        "libnativehelper/header_only_include",
     ],
     header_libs: [
         "libopenjdkjvmti_headers",
@@ -33,6 +35,8 @@ cc_binary_host {
     include_dirs: [
         // NDK headers aren't available in platform NDK builds.
         "libnativehelper/include_jni",
+        // Use ScopedUtfChars.
+        "libnativehelper/header_only_include",
     ],
     header_libs: [
         "libopenjdkjvmti_headers",

tools/lock_agent/agent.cpp

@@ -19,6 +19,8 @@
 #include <memory>
 #include <sstream>
 
+#include <unistd.h>
+
 #include <jni.h>
 
 #include <jvmti.h>
@@ -26,10 +28,14 @@
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/macros.h>
+#include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 
 #include <fcntl.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
+
+#include <nativehelper/scoped_utf_chars.h>
 
 // We need dladdr.
 #if !defined(__APPLE__) && !defined(_WIN32)
@@ -61,6 +67,7 @@
 namespace {
 
 JavaVM* gJavaVM = nullptr;
+bool gForkCrash = false;
 
 // Converts a class name to a type descriptor
 // (ex. "java.lang.String" to "Ljava/lang/String;")
@@ -372,7 +379,7 @@ void prepareHook(jvmtiEnv* env) {
     }
 }
 
-jint attach(JavaVM* vm, char* options ATTRIBUTE_UNUSED, void* reserved ATTRIBUTE_UNUSED) {
+jint attach(JavaVM* vm, char* options, void* reserved ATTRIBUTE_UNUSED) {
     gJavaVM = vm;
 
     jvmtiEnv* env;
@@ -383,9 +390,59 @@ jint attach(JavaVM* vm, char* options ATTRIBUTE_UNUSED, void* reserved ATTRIBUTE
 
     prepareHook(env);
 
+    std::vector<std::string> config = android::base::Split(options, ",");
+    for (const std::string& c : config) {
+        if (c == "native_crash") {
+            gForkCrash = true;
+        }
+    }
+
     return JVMTI_ERROR_NONE;
 }
 
+extern "C" JNIEXPORT
+jboolean JNICALL Java_com_android_lock_1checker_LockHook_getNativeHandlingConfig(JNIEnv*, jclass) {
+    return gForkCrash ? JNI_TRUE : JNI_FALSE;
+}
+
+extern "C" JNIEXPORT void JNICALL Java_com_android_lock_1checker_LockHook_nWtf(JNIEnv* env, jclass,
+        jstring msg) {
+    if (!gForkCrash || msg == nullptr) {
+        return;
+    }
+
+    // Create a native crash with the given message. Decouple from the current crash to create a
+    // tombstone but continue on.
+    //
+    // TODO: Once there are not so many reports, consider making this fatal for the calling process.
+    ScopedUtfChars utf(env, msg);
+    if (utf.c_str() == nullptr) {
+        return;
+    }
+    const char* args[] = {
+        "/system/bin/lockagent_crasher",
+        utf.c_str(),
+        nullptr
+    };
+    pid_t pid = fork();
+    if (pid < 0) {
+        return;
+    }
+    if (pid == 0) {
+        // Double fork so we return quickly. Leave init to deal with the zombie.
+        pid_t pid2 = fork();
+        if (pid2 == 0) {
+            execv(args[0], const_cast<char* const*>(args));
+            _exit(1);
+            __builtin_unreachable();
+        }
+        _exit(0);
+        __builtin_unreachable();
+    }
+    int status;
+    waitpid(pid, &status, 0);  // Ignore any results.
+}
+
 extern "C" JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM* vm, char* options, void* reserved) {
     return attach(vm, options, reserved);
 }

tools/lock_agent/java/com/android/lock_checker/LockHook.java

@@ -72,14 +72,20 @@ public class LockHook {
 
     private static final LockChecker[] sCheckers;
 
+    private static boolean sNativeHandling = false;
+
     static {
         sHandlerThread = new HandlerThread("LockHook:wtf", Process.THREAD_PRIORITY_BACKGROUND);
         sHandlerThread.start();
         sHandler = new WtfHandler(sHandlerThread.getLooper());
 
         sCheckers = new LockChecker[] { new OnThreadLockChecker() };
+
+        sNativeHandling = getNativeHandlingConfig();
     }
 
+    private static native boolean getNativeHandlingConfig();
+
     static <T> boolean shouldDumpStacktrace(StacktraceHasher hasher, Map<String, T> dumpedSet,
             T val, AnnotatedStackTraceElement[] st, int from, int to) {
         final String stacktraceHash = hasher.stacktraceHash(st, from, to);
@@ -175,8 +181,13 @@ public class LockHook {
     private static void handleViolation(Violation v) {
         String msg = v.toString();
         Log.wtf(TAG, msg);
+        if (sNativeHandling) {
+            nWtf(msg);  // Also send to native.
+        }
     }
 
+    private static native void nWtf(String msg);
+
     /**
      * Generates a hash for a given stacktrace of a {@link Throwable}.
      */