[ARM] add address randomization to mmap()

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

arch/arm/mm/mmap.c

@@ -7,6 +7,7 @@
 #include <linux/shm.h>
 #include <linux/sched.h>
 #include <linux/io.h>
+#include <linux/random.h>
 #include <asm/cputype.h>
 #include <asm/system.h>
 
@@ -80,6 +81,9 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	        start_addr = addr = TASK_UNMAPPED_BASE;
 	        mm->cached_hole_size = 0;
 	}
+	/* 8 bits of randomness in 20 address space bits */
+	if (current->flags & PF_RANDOMIZE)
+		addr += (get_random_int() % (1 << 8)) << PAGE_SHIFT;
 
 full_search:
 	if (do_align)