ARC: Fix 32-bit wrap around in access_ok()

Anton reported

| LTP tests syscalls/process_vm_readv01 and process_vm_writev01 fail
| similarly in one testcase test_iov_invalid -> lvec->iov_base.
| Testcase expects errno EFAULT and return code -1,
| but it gets return code 1 and ERRNO is 0 what means success.

Essentially test case was passing a pointer of -1 which access_ok()
was not catching. It was doing [@addr + @sz <= TASK_SIZE] which would
pass for @addr == -1

Fixed that by rewriting as [@addr <= TASK_SIZE - @sz]

Reported-by: Anton Kolesov <[e-mail]>
Signed-off-by: Vineet Gupta <[e-mail]>

arch/arc/include/asm/uaccess.h

···
  * Because it essentially checks if buffer end is within limit and @len is
  * non-ngeative, which implies that buffer start will be within limit too.
  *
- * The reason for rewriting being, for majorit yof cases, @len is generally
+ * The reason for rewriting being, for majority of cases, @len is generally
  * compile time constant, causing first sub-expression to be compile time
  * subsumed.
  *
···
  *
  */
 #define __user_ok(addr, sz)	(((sz) <= TASK_SIZE) && \
-				 (((addr)+(sz)) <= get_fs()))
+				 ((addr) <= (get_fs() - (sz))))
 #define __access_ok(addr, sz)	(unlikely(__kernel_ok) || \
 				 likely(__user_ok((addr), (sz))))