1 files changed, 29 insertions, 0 deletions
diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 52526aa..a699784 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -9,9 +9,11 @@
 #include "filesys/filesys.h"
 #include "filesys/off_t.h"
 #include "lib/pid_t.h"
+#include "userprog/pagedir.h"
 #include "userprog/process.h"
 #include "threads/init.h"
 #include "threads/malloc.h"
+#include "threads/vaddr.h"
 
 static void syscall_handler (struct intr_frame *);
 
@@ -162,13 +164,40 @@ exec (const char *file_name)
   return process_execute (file_name);
 }
 
+static bool
+ptr_is_valid (const void *ptr)
+{
+  // uintptr_t ptr = _ptr;
+  if (!is_user_vaddr (ptr))
+    return false;
+
+  struct thread *t = thread_current ();
+
+  if (pagedir_get_page (t->pagedir, ptr) == NULL)
+    return false;
+
+  return true;
+}
+
 // cast to TYPE and deref argument N from f->esp
 #define INTR_ESP(N, TYPE) *(TYPE *)(f->esp+(4*(N)))
 
+#define CHECK_ESP_AND_MAYBE_EXIT(N)          \
+  do {                                       \
+    if (!ptr_is_valid ((f->esp+(4*(N))))) {  \
+      exit (-1);                             \
+      return;                                \
+    }                                        \
+  } while (0)
+
+
 static void
 syscall_handler (struct intr_frame *f UNUSED) 
 {
+  // check esp
+  CHECK_ESP_AND_MAYBE_EXIT (0);
   int syscall_number = INTR_ESP (0, int);
+
   switch (syscall_number) {
     case 0:
       // halt