-fsanitize=vptr warnings on bad static types in dynamic_cast and typeid

...when such an operation is done on an object during con-/destruction.

This is the cfe part of a patch covering both cfe and compiler-rt.

Differential Revision: https://reviews.llvm.org/D40295

llvm-svn: 321519

clang/lib/CodeGen/CGExpr.cpp

@@ -570,7 +570,7 @@ static llvm::Value *emitHash16Bytes(CGBuilderTy &Builder, llvm::Value *Low,
 
 bool CodeGenFunction::isNullPointerAllowed(TypeCheckKind TCK) {
   return TCK == TCK_DowncastPointer || TCK == TCK_Upcast ||
-         TCK == TCK_UpcastToVirtualBase;
+         TCK == TCK_UpcastToVirtualBase || TCK == TCK_DynamicOperation;
 }
 
 bool CodeGenFunction::isVptrCheckRequired(TypeCheckKind TCK, QualType Ty) {
@@ -578,7 +578,7 @@ bool CodeGenFunction::isVptrCheckRequired(TypeCheckKind TCK, QualType Ty) {
   return (RD && RD->hasDefinition() && RD->isDynamicClass()) &&
          (TCK == TCK_MemberAccess || TCK == TCK_MemberCall ||
           TCK == TCK_DowncastPointer || TCK == TCK_DowncastReference ||
-          TCK == TCK_UpcastToVirtualBase);
+          TCK == TCK_UpcastToVirtualBase || TCK == TCK_DynamicOperation);
 }
 
 bool CodeGenFunction::sanitizePerformTypeCheck() const {

clang/lib/CodeGen/CGExprCXX.cpp

@@ -2056,6 +2056,15 @@ static llvm::Value *EmitTypeidFromVTable(CodeGenFunction &CGF, const Expr *E,
   // Get the vtable pointer.
   Address ThisPtr = CGF.EmitLValue(E).getAddress();
 
+  QualType SrcRecordTy = E->getType();
+
+  // C++ [class.cdtor]p4:
+  //   If the operand of typeid refers to the object under construction or
+  //   destruction and the static type of the operand is neither the constructor
+  //   or destructor’s class nor one of its bases, the behavior is undefined.
+  CGF.EmitTypeCheck(CodeGenFunction::TCK_DynamicOperation, E->getExprLoc(),
+                    ThisPtr.getPointer(), SrcRecordTy);
+
   // C++ [expr.typeid]p2:
   //   If the glvalue expression is obtained by applying the unary * operator to
   //   a pointer and the pointer is a null pointer value, the typeid expression
@@ -2064,7 +2073,6 @@ static llvm::Value *EmitTypeidFromVTable(CodeGenFunction &CGF, const Expr *E,
   // However, this paragraph's intent is not clear.  We choose a very generous
   // interpretation which implores us to consider comma operators, conditional
   // operators, parentheses and other such constructs.
-  QualType SrcRecordTy = E->getType();
   if (CGF.CGM.getCXXABI().shouldTypeidBeNullChecked(
           isGLValueFromPointerDeref(E), SrcRecordTy)) {
     llvm::BasicBlock *BadTypeidBlock =
@@ -2127,10 +2135,6 @@ llvm::Value *CodeGenFunction::EmitDynamicCast(Address ThisAddr,
   CGM.EmitExplicitCastExprType(DCE, this);
   QualType DestTy = DCE->getTypeAsWritten();
 
-  if (DCE->isAlwaysNull())
-    if (llvm::Value *T = EmitDynamicCastToNull(*this, DestTy))
-      return T;
-
   QualType SrcTy = DCE->getSubExpr()->getType();
 
   // C++ [expr.dynamic.cast]p7:
@@ -2151,6 +2155,18 @@ llvm::Value *CodeGenFunction::EmitDynamicCast(Address ThisAddr,
     DestRecordTy = DestTy->castAs<ReferenceType>()->getPointeeType();
   }
 
+  // C++ [class.cdtor]p5:
+  //   If the operand of the dynamic_cast refers to the object under
+  //   construction or destruction and the static type of the operand is not a
+  //   pointer to or object of the constructor or destructor’s own class or one
+  //   of its bases, the dynamic_cast results in undefined behavior.
+  EmitTypeCheck(TCK_DynamicOperation, DCE->getExprLoc(), ThisAddr.getPointer(),
+                SrcRecordTy);
+
+  if (DCE->isAlwaysNull())
+    if (llvm::Value *T = EmitDynamicCastToNull(*this, DestTy))
+      return T;
+
   assert(SrcRecordTy->isRecordType() && "source type must be a record type!");
 
   // C++ [expr.dynamic.cast]p4: 

clang/lib/CodeGen/CodeGenFunction.h

@@ -2371,7 +2371,10 @@ public:
     /// object within its lifetime.
     TCK_UpcastToVirtualBase,
     /// Checking the value assigned to a _Nonnull pointer. Must not be null.
-    TCK_NonnullAssign
+    TCK_NonnullAssign,
+    /// Checking the operand of a dynamic_cast or a typeid expression.  Must be
+    /// null or an object within its lifetime.
+    TCK_DynamicOperation
   };
 
   /// Determine whether the pointer type check \p TCK permits null pointers.

clang/test/CodeGenCXX/ubsan-vtable-checks.cpp

@@ -38,3 +38,15 @@ void delete_it(T *t) {
   // CHECK-VPTR: load {{.*}} (%struct.T*{{.*}})**, {{.*}} (%struct.T*{{.*}})***
   delete t;
 }
+
+// ITANIUM: define %struct.U* @_Z7dyncastP1T
+// MSABI: define %struct.U* @"\01?dyncast
+U* dyncast(T *t) {
+  // First, we check that dynamic_cast is not called before a type check.
+  // CHECK-VPTR-NOT: call i8* @__{{dynamic_cast|RTDynamicCast}}
+  // CHECK-VPTR: br i1 {{.*}} label %{{.*}}
+  // CHECK-VPTR: call void @__ubsan_handle_dynamic_type_cache_miss_abort
+  // Second, we check that dynamic_cast is actually called once the type check is done.
+  // CHECK-VPTR: call i8* @__{{dynamic_cast|RTDynamicCast}}
+  return dynamic_cast<U*>(t);
+}