Update validate_user_pointer to check if the ptr is mapped to a physical memory address, w/ E

src/userprog/syscall.c

@@ -5,6 +5,7 @@
 #include "threads/interrupt.h"
 #include "threads/thread.h"
 #include "userprog/process.h"
+#include "userprog/pagedir.h"
 #include <stdio.h>
 #include <syscall-nr.h>
 
@@ -227,8 +228,9 @@ validate_user_pointer (const void *ptr, size_t size)
 {
   if (size > 0 && (ptr == NULL ||
                    !is_user_vaddr (ptr) ||
-                   !is_user_vaddr (ptr + size - 1)))
+                   !is_user_vaddr (ptr + size - 1) ||
+                   pagedir_get_page (thread_current()->pagedir, ptr) == NULL))
     thread_exit ();
 
-  return ptr;
+  return (void *) ptr;
 }