6539281: -Xcheck:jni should validate char* argument to ReleaseStringUTFChars

Tag allocated memory with a magic value and verify when releasing.

Reviewed-by: phh, stefank

hotspot/src/share/vm/classfile/javaClasses.cpp

@@ -313,6 +313,14 @@ char* java_lang_String::as_utf8_string(oop java_string) {
   return UNICODE::as_utf8(position, length);
 }
 
+char* java_lang_String::as_utf8_string(oop java_string, char* buf, int buflen) {
+  typeArrayOop value  = java_lang_String::value(java_string);
+  int          offset = java_lang_String::offset(java_string);
+  int          length = java_lang_String::length(java_string);
+  jchar* position = (length == 0) ? NULL : value->char_at_addr(offset);
+  return UNICODE::as_utf8(position, length, buf, buflen);
+}
+
 char* java_lang_String::as_utf8_string(oop java_string, int start, int len) {
   typeArrayOop value  = java_lang_String::value(java_string);
   int          offset = java_lang_String::offset(java_string);

hotspot/src/share/vm/classfile/javaClasses.hpp

@@ -104,6 +104,7 @@ class java_lang_String : AllStatic {
 
   // String converters
   static char*  as_utf8_string(oop java_string);
+  static char*  as_utf8_string(oop java_string, char* buf, int buflen);
   static char*  as_utf8_string(oop java_string, int start, int len);
   static char*  as_platform_dependent_str(Handle java_string, TRAPS);
   static jchar* as_unicode_string(oop java_string, int& length);

hotspot/src/share/vm/prims/jni.cpp

@@ -2113,11 +2113,10 @@ JNI_END
 JNI_ENTRY(const char*, jni_GetStringUTFChars(JNIEnv *env, jstring string, jboolean *isCopy))
   JNIWrapper("GetStringUTFChars");
   DTRACE_PROBE3(hotspot_jni, GetStringUTFChars__entry, env, string, isCopy);
-  ResourceMark rm;
+  oop java_string = JNIHandles::resolve_non_null(string);
-  char* str = java_lang_String::as_utf8_string(JNIHandles::resolve_non_null(string));
+  size_t length = java_lang_String::utf8_length(java_string);
-  int length = (int)strlen(str);
+  char* result = AllocateHeap(length + 1, "GetStringUTFChars");
-  char* result = AllocateHeap(length+1, "GetStringUTFChars");
+  java_lang_String::as_utf8_string(java_string, result, (int) length + 1);
-  strcpy(result, str);
   if (isCopy != NULL) *isCopy = JNI_TRUE;
   DTRACE_PROBE1(hotspot_jni, GetStringUTFChars__return, result);
   return result;

hotspot/src/share/vm/prims/jniCheck.cpp

@@ -1288,6 +1288,9 @@ JNI_ENTRY_CHECKED(jsize,
     return result;
 JNI_END
 
+// Arbitrary (but well-known) tag
+const jint STRING_TAG = 0x47114711;
+
 JNI_ENTRY_CHECKED(const jchar *,
   checked_jni_GetStringChars(JNIEnv *env,
                              jstring str,
@@ -1297,8 +1300,19 @@ JNI_ENTRY_CHECKED(const jchar *,
       checkString(thr, str);
     )
     const jchar *result = UNCHECKED()->GetStringChars(env,str,isCopy);
+    assert (isCopy == NULL || *isCopy == JNI_TRUE, "GetStringChars didn't return a copy as expected");
+
+    size_t len = UNCHECKED()->GetStringLength(env,str) + 1; // + 1 for NULL termination
+    jint* tagLocation = (jint*) AllocateHeap(len * sizeof(jchar) + sizeof(jint), "checked_jni_GetStringChars");
+    *tagLocation = STRING_TAG;
+    jchar* newResult = (jchar*) (tagLocation + 1);
+    memcpy(newResult, result, len * sizeof(jchar));
+    // Avoiding call to UNCHECKED()->ReleaseStringChars() since that will fire unexpected dtrace probes
+    // Note that the dtrace arguments for the allocated memory will not match up with this solution.
+    FreeHeap((char*)result);
+
     functionExit(env);
-    return result;
+    return newResult;
 JNI_END
 
 JNI_ENTRY_CHECKED(void,
@@ -1309,11 +1323,17 @@ JNI_ENTRY_CHECKED(void,
     IN_VM(
       checkString(thr, str);
     )
-    /* cannot check validity of copy, unless every request is logged by
+    if (chars == NULL) {
-     * checking code.  Implementation of this check is deferred until a
+       // still do the unchecked call to allow dtrace probes
-     * subsequent release.
+       UNCHECKED()->ReleaseStringChars(env,str,chars);
-     */
+    }
-    UNCHECKED()->ReleaseStringChars(env,str,chars);
+    else {
+       jint* tagLocation = ((jint*) chars) - 1;
+       if (*tagLocation != STRING_TAG) {
+          NativeReportJNIFatalError(thr, "ReleaseStringChars called on something not allocated by GetStringChars");
+       }
+       UNCHECKED()->ReleaseStringChars(env,str,(const jchar*)tagLocation);
+    }
     functionExit(env);
 JNI_END
 
@@ -1338,6 +1358,9 @@ JNI_ENTRY_CHECKED(jsize,
     return result;
 JNI_END
 
+// Arbitrary (but well-known) tag - different than GetStringChars
+const jint STRING_UTF_TAG = 0x48124812;
+
 JNI_ENTRY_CHECKED(const char *,
   checked_jni_GetStringUTFChars(JNIEnv *env,
                                 jstring str,
@@ -1347,8 +1370,19 @@ JNI_ENTRY_CHECKED(const char *,
       checkString(thr, str);
     )
     const char *result = UNCHECKED()->GetStringUTFChars(env,str,isCopy);
+    assert (isCopy == NULL || *isCopy == JNI_TRUE, "GetStringUTFChars didn't return a copy as expected");
+
+    size_t len = strlen(result) + 1; // + 1 for NULL termination
+    jint* tagLocation = (jint*) AllocateHeap(len + sizeof(jint), "checked_jni_GetStringUTFChars");
+    *tagLocation = STRING_UTF_TAG;
+    char* newResult = (char*) (tagLocation + 1);
+    strcpy(newResult, result);
+    // Avoiding call to UNCHECKED()->ReleaseStringUTFChars() since that will fire unexpected dtrace probes
+    // Note that the dtrace arguments for the allocated memory will not match up with this solution.
+    FreeHeap((char*)result);
+
     functionExit(env);
-    return result;
+    return newResult;
 JNI_END
 
 JNI_ENTRY_CHECKED(void,
@@ -1359,11 +1393,17 @@ JNI_ENTRY_CHECKED(void,
     IN_VM(
       checkString(thr, str);
     )
-    /* cannot check validity of copy, unless every request is logged by
+    if (chars == NULL) {
-     * checking code.  Implementation of this check is deferred until a
+       // still do the unchecked call to allow dtrace probes
-     * subsequent release.
+       UNCHECKED()->ReleaseStringUTFChars(env,str,chars);
-     */
+    }
-    UNCHECKED()->ReleaseStringUTFChars(env,str,chars);
+    else {
+       jint* tagLocation = ((jint*) chars) - 1;
+       if (*tagLocation != STRING_UTF_TAG) {
+          NativeReportJNIFatalError(thr, "ReleaseStringUTFChars called on something not allocated by GetStringUTFChars");
+       }
+       UNCHECKED()->ReleaseStringUTFChars(env,str,(const char*)tagLocation);
+    }
     functionExit(env);
 JNI_END