Add more tests for system calls to deal with bad buffers given to read and write

src/tests/userprog/write-bad-buf.c

@@ -0,0 +1,17 @@
+/* Passes a buffer to the write system call that starts in valid memory, but runs into kernel space.
+   The process must be terminated with -1 exit code.
+*/
+
+#include <syscall.h>
+#include "tests/lib.h"
+#include "tests/main.h"
+
+void
+test_main (void)
+{
+  int handle;
+  CHECK ((handle = open ("sample.txt")) > 1, "open \"sample.txt\"");
+
+  write (handle, (char *) 0xbffffff0, 32);
+  fail ("should have exited with -1");
+}