s390/uaccess: add missing page table walk range check

When translating a user space address, the address must be checked against
the ASCE limit of the process. If the address is larger than the maximum
address that is reachable with the ASCE, an ASCE type exception must be
generated.

The current code simply ignored the higher order bits. This resulted in an
address wrap around in user space instead of an exception in user space.

Cc: stable@vger.kernel.org # v3.9+
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/lib/uaccess_pt.c

@@ -78,11 +78,14 @@ static size_t copy_in_kernel(size_t count, void __user *to,
  * contains the (negative) exception code.
  */
 #ifdef CONFIG_64BIT
+
 static unsigned long follow_table(struct mm_struct *mm,
 				  unsigned long address, int write)
 {
 	unsigned long *table = (unsigned long *)__pa(mm->pgd);
 
+	if (unlikely(address > mm->context.asce_limit - 1))
+		return -0x38UL;
 	switch (mm->context.asce_bits & _ASCE_TYPE_MASK) {
 	case _ASCE_TYPE_REGION1:
 		table = table + ((address >> 53) & 0x7ff);