[Stack Switching] Validate continuation function subtyping (#7847)

Author: kripken

src/wasm/wasm-validator.cpp

@@ -3979,10 +3979,18 @@ void FunctionValidator::visitContNew(ContNew* curr) {
   }
   shouldBeTrue(curr->type.isExact(), curr, "cont.new should be exact");
 
-  shouldBeTrue(curr->type.isContinuation() &&
-                 curr->type.getHeapType().getContinuation().type.isSignature(),
+  if (!shouldBeTrue(curr->type.isContinuation(),
+                    curr,
+                    "cont.new must be annotated with a continuation type")) {
+    return;
+  }
+
+  auto cont = curr->type.getHeapType().getContinuation();
+  assert(cont.type.isSignature());
+
+  shouldBeTrue(HeapType::isSubType(curr->func->type.getHeapType(), cont.type),
                curr,
-               "cont.new must be annotated with a continuation type");
+               "cont.new function reference must be a subtype");
 }
 
 void FunctionValidator::visitContBind(ContBind* curr) {

test/spec/cont.wast

@@ -242,6 +242,26 @@
   (type $c2 (cont $f2))
 )
 
+(assert_invalid
+  (module
+    (rec
+      (type $fA (func))
+      (type $fB (func))
+      (type $cont (cont $fA))
+    )
+    (elem declare func $b)
+    (func $a
+      (drop
+        (cont.new $cont ;; expects a ref of $fA, not $fB
+          (ref.func $b)
+        )
+      )
+    )
+    (func $b (type $fB)
+    )
+  )
+  "type mismatch")
+
 ;; Simple state example
 
 (module $state