[analyzer] pr36458: Fix retrieved value cast for symbolic void pointers.

C allows us to write any bytes into any memory region. When loading weird bytes
from memory regions of known types, the analyzer is required to make sure that
the loaded value makes sense by casting it to an appropriate type.

Fix such cast for loading values that represent void pointers from non-void
pointer type places.

Differential Revision: https://reviews.llvm.org/D46415

llvm-svn: 331562

clang/lib/StaticAnalyzer/Core/Store.cpp

@@ -378,6 +378,20 @@ SVal StoreManager::CastRetrievedVal(SVal V, const TypedValueRegion *R,
   if (castTy.isNull() || V.isUnknownOrUndef())
     return V;
 
+  // When retrieving symbolic pointer and expecting a non-void pointer,
+  // wrap them into element regions of the expected type if necessary.
+  // SValBuilder::dispatchCast() doesn't do that, but it is necessary to
+  // make sure that the retrieved value makes sense, because there's no other
+  // cast in the AST that would tell us to cast it to the correct pointer type.
+  // We might need to do that for non-void pointers as well.
+  // FIXME: We really need a single good function to perform casts for us
+  // correctly every time we need it.
+  if (castTy->isPointerType() && !castTy->isVoidPointerType())
+    if (const auto *SR = dyn_cast_or_null<SymbolicRegion>(V.getAsRegion()))
+      if (SR->getSymbol()->getType().getCanonicalType() !=
+          castTy.getCanonicalType())
+        return loc::MemRegionVal(castRegion(SR, castTy));
+
   return svalBuilder.dispatchCast(V, castTy);
 }
 

clang/test/Analysis/casts.c

@@ -149,3 +149,25 @@ void multiDimensionalArrayPointerCasts() {
 
   clang_analyzer_eval(*((char *)y1) == *((char *) y3)); // expected-warning{{TRUE}}
 }
+
+void *getVoidPtr();
+
+void testCastVoidPtrToIntPtrThroughIntTypedAssignment() {
+  int *x;
+  (*((int *)(&x))) = (int)getVoidPtr();
+  *x = 1; // no-crash
+}
+
+void testCastUIntPtrToIntPtrThroughIntTypedAssignment() {
+  unsigned u;
+  int *x;
+  (*((int *)(&x))) = (int)&u;
+  *x = 1;
+  clang_analyzer_eval(u == 1); // expected-warning{{TRUE}}
+}
+
+void testCastVoidPtrToIntPtrThroughUIntTypedAssignment() {
+  int *x;
+  (*((int *)(&x))) = (int)(unsigned *)getVoidPtr();
+  *x = 1; // no-crash
+}