[S390] Randomize lower bits of stack address

Randomize the lower bits of the stack address like x86 and powerpc.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/system.h

@@ -449,7 +449,7 @@ extern void (*_machine_restart)(char *command);
 extern void (*_machine_halt)(void);
 extern void (*_machine_power_off)(void);
 
-#define arch_align_stack(x) (x)
+extern unsigned long arch_align_stack(unsigned long sp);
 
 static inline int tprot(unsigned long addr)
 {

arch/s390/kernel/process.c

@@ -30,9 +30,11 @@
 #include <linux/tick.h>
 #include <linux/elfcore.h>
 #include <linux/kernel_stat.h>
+#include <linux/personality.h>
 #include <linux/syscalls.h>
 #include <linux/compat.h>
 #include <linux/kprobes.h>
+#include <linux/random.h>
 #include <asm/compat.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
@@ -332,3 +334,10 @@ unsigned long get_wchan(struct task_struct *p)
 	}
 	return 0;
 }
+
+unsigned long arch_align_stack(unsigned long sp)
+{
+	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
+		sp -= get_random_int() & ~PAGE_MASK;
+	return sp & ~0xf;
+}