8238460: Provide warnings about the use of JNI RegisterNatives to rebind native methods for boot/platform classes in other classloaders

Reviewed-by: jwilhelm, lfoltan

src/hotspot/share/prims/jni.cpp

@@ -2811,6 +2811,20 @@ JNI_ENTRY(jint, jni_RegisterNatives(JNIEnv *env, jclass clazz,
 
   Klass* k = java_lang_Class::as_Klass(JNIHandles::resolve_non_null(clazz));
 
+  // There are no restrictions on native code registering native methods, which
+  // allows agents to redefine the bindings to native methods. But we issue a
+  // warning if any code running outside of the boot/platform loader is rebinding
+  // any native methods in classes loaded by the boot/platform loader.
+  Klass* caller = thread->security_get_caller_class(1);
+  bool do_warning = false;
+  oop cl = k->class_loader();
+  if (cl ==  NULL || SystemDictionary::is_platform_class_loader(cl)) {
+    // If no caller class, or caller class has a different loader, then
+    // issue a warning below.
+    do_warning = (caller == NULL) || caller->class_loader() != cl;
+  }
+
+
   for (int index = 0; index < nMethods; index++) {
     const char* meth_name = methods[index].name;
     const char* meth_sig = methods[index].signature;
@@ -2823,13 +2837,19 @@ JNI_ENTRY(jint, jni_RegisterNatives(JNIEnv *env, jclass clazz,
     TempNewSymbol  signature = SymbolTable::probe(meth_sig, (int)strlen(meth_sig));
 
     if (name == NULL || signature == NULL) {
-      ResourceMark rm;
+      ResourceMark rm(THREAD);
       stringStream st;
       st.print("Method %s.%s%s not found", k->external_name(), meth_name, meth_sig);
       // Must return negative value on failure
       THROW_MSG_(vmSymbols::java_lang_NoSuchMethodError(), st.as_string(), -1);
     }
 
+    if (do_warning) {
+      ResourceMark rm(THREAD);
+      log_warning(jni, resolve)("Re-registering of platform native method: %s.%s%s "
+              "from code in a different classloader", k->external_name(), meth_name, meth_sig);
+    }
+
     bool res = Method::register_native(k, name, signature,
                                        (address) methods[index].fnPtr, THREAD);
     if (!res) {

test/hotspot/jtreg/runtime/jni/registerNativesWarning/TestRegisterNativesWarning.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.process.ProcessTools;
+
+/*
+ * @test
+ * @bug 8238460
+ * @summary Check that re-registering a native method of a boot class
+ *          generates a warning when not done from a boot class
+ *
+ * @library /test/lib
+ * @run main/othervm/native TestRegisterNativesWarning
+ */
+
+public class TestRegisterNativesWarning {
+
+    static {
+        System.loadLibrary("registerNativesWarning");
+    }
+
+    /*
+     * We will replace:
+     *   java/lang/Thread.java:    public static native void yield();
+     *
+     * as it is simple and innocuous.
+     */
+    native static void test(Class<?> jlThread);
+
+    // Using a nested class that invokes an enclosing method makes it
+    // easier to setup and use the native library.
+    static class Tester {
+        public static void main(String[] args) throws Exception {
+            System.out.println("Running test() in class loader " +
+                               Tester.class.getClassLoader());
+            test(Thread.class);
+            Thread.yield();
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        String warning = "Re-registering of platform native method: java.lang.Thread.yield()V from code in a different classloader";
+
+        OutputAnalyzer output = ProcessTools.executeTestJvm(Tester.class.getName());
+        output.shouldContain(warning);
+        output.shouldHaveExitValue(0);
+        output.reportDiagnosticSummary();
+
+        // If we run everything from the "boot" loader there should be no warning
+        String cp = System.getProperty("test.class.path");
+        String libp = System.getProperty("java.library.path");
+        output = ProcessTools.executeTestJvm("-Xbootclasspath/a:" + cp,
+                                             "-Dsun.boot.library.path=" + libp,
+                                             Tester.class.getName());
+        output.shouldNotContain(warning);
+        output.shouldHaveExitValue(0);
+        output.reportDiagnosticSummary();
+    }
+}

test/hotspot/jtreg/runtime/jni/registerNativesWarning/libregisterNativesWarning.c

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include <stdio.h>
+
+#include "jni.h"
+#include "jni_util.h"
+
+/*
+ * We will replace:
+ *   java/lang/Thread.java:    public static native void yield();
+ *
+ * as it is simple and innocuous.
+ */
+static void myYield(JNIEnv* env, jclass cls) {
+  printf("myYield executed\n");
+}
+
+
+JNIEXPORT void JNICALL
+Java_TestRegisterNativesWarning_test
+(JNIEnv *env, jclass cls, jclass jlThread) {
+  JNINativeMethod nativeMethods[] = {
+    {
+      (char*) "yield",  // name
+      (char*) "()V",    // sig
+      (void*) myYield   // native method ptr
+    }
+  };
+  (*env)->RegisterNatives(env, jlThread, nativeMethods, 1);
+}