Mitigating VMMethod::id() crash (#359)

Author: zhengyu123

ddprof-lib/src/main/cpp/safeAccess.h

@@ -73,6 +73,11 @@ class SafeAccess {
 
   NOINLINE __attribute__((aligned(16)))
   static void *loadPtr(void** ptr, void* default_value);
+
+  static inline bool isReadable(void* ptr) {
+    return load32((int32_t*)ptr, 1) != 1 ||
+           load32((int32_t*)ptr, -1) != -1; 
+  }
 };
 
 #endif // _SAFEACCESS_H

ddprof-lib/src/main/cpp/stackWalker.cpp

@@ -59,7 +59,7 @@ static inline void fillFrame(ASGCT_CallFrame& frame, FrameTypeId type, int bci,
 }
 
 static jmethodID getMethodId(VMMethod* method) {
-    if (!inDeadZone(method) && aligned((uintptr_t)method)) {
+    if (!inDeadZone(method) && aligned((uintptr_t)method) && SafeAccess::isReadable((void*)method)) {
         return method->validatedId();
     }
     return NULL;

ddprof-lib/src/test/cpp/safefetch_ut.cpp

@@ -105,6 +105,12 @@ TEST_F(SafeFetchTest, invalidAccessPtr) {
   EXPECT_EQ(res, bp);
 }
 
+TEST_F(SafeFetchTest, isReadable) {
+  char c = 'x';
+  EXPECT_TRUE(SafeAccess::isReadable(&c));
+  EXPECT_FALSE(SafeAccess::isReadable(nullptr));
+}
+
 /**
  * Tests that safeFetch32 correctly handles mprotected memory.
  *