more incorrect cast to uint

user/usertests.c

@@ -1908,15 +1908,18 @@ stacktest(char *s)
     exit(xstatus);
 }
 
-// copyinstr() used to cast the virtual page address to uint,
-// which (with certain wild system call arguments) could
-// result in a kernel page fault.
+// copyin(), copyout(), and copyinstr() used to cast the virtual page
+// address to uint, which (with certain wild system call arguments)
+// resulted in a kernel page faults.
 void
 pgbug(char *s)
 {
   char *argv[1];
   argv[0] = 0;
   exec((char*)0xeaeb0b5b00002f5e, argv);
+
+  pipe((int*)0xeaeb0b5b00002f5e);
+
   exit(0);
 }