x86: Fix norandmaps/ADDR_NO_RANDOMIZE

Documentation/admin-guide/kernel-parameters.txt says:

    norandmaps  Don't use address space randomization. Equivalent
                to echo 0 > /proc/sys/kernel/randomize_va_space

but it doesn't work because arch_rnd() which is used to randomize
mm->mmap_base returns a random value unconditionally. And as Kirill
pointed out, ADDR_NO_RANDOMIZE is broken by the same reason.

Just shift the PF_RANDOMIZE check from arch_mmap_rnd() to arch_rnd().

Fixes: 1b028f7 ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()")
Signed-off-by: Oleg Nesterov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Acked-by: Cyrill Gorcunov <[email protected]>
Reviewed-by: Dmitry Safonov <[email protected]>
Cc: [email protected]
Cc: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]

arch/x86/mm/mmap.c

@@ -79,13 +79,13 @@ static int mmap_is_legacy(void)
 
 static unsigned long arch_rnd(unsigned int rndbits)
 {
+	if (!(current->flags & PF_RANDOMIZE))
+		return 0;
 	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
 }
 
 unsigned long arch_mmap_rnd(void)
 {
-	if (!(current->flags & PF_RANDOMIZE))
-		return 0;
 	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
 }