ARM: use simpler API for random address requests

Currently, all callers to randomize_range() set the length to 0 and
calculate end by adding a constant to the start address.  We can simplify
the API to remove a bunch of needless checks and variables.

Use the new randomize_addr(start, range) call to set the requested
address.

Link: http://lkml.kernel.org/r/20160803233913.32511-4-jason@lakedaemon.netSigned-off-by: NJason Cooper <jason@lakedaemon.net>
Acked-by: NKees Cook <keescook@chromium.org>
Cc: "Russell King - ARM Linux" <linux@arm.linux.org.uk>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/arm/kernel/process.c

@@ -318,8 +318,7 @@ unsigned long get_wchan(struct task_struct *p)
 
 unsigned long arch_randomize_brk(struct mm_struct *mm)
 {
-	unsigned long range_end = mm->brk + 0x02000000;
-	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
+	return randomize_page(mm->brk, 0x02000000);
 }
 
 #ifdef CONFIG_MMU