arm64/mm: Remove hack in mmap randomize layout

commit d6c763afab142a85e4770b4bc2a5f40f256d5c5d upstream.

Since commit 8a0a9bd4db63 ('random: make get_random_int() more
random'), get_random_int() returns a random value for each call,
so comment and hack introduced in mmap_rnd() as part of commit
1d18c47c735e ('arm64: MMU fault handling and page table management')
are incorrects.

Commit 1d18c47c735e seems to use the same hack introduced by
commit a5adc91a4b44 ('powerpc: Ensure random space between stack
and mmaps'), latter copied in commit 5a0efea09f42 ('sparc64: Sharpen
address space randomization calculations.').

But both architectures were cleaned up as part of commit
fa8cbaaf5a68 ('powerpc+sparc64/mm: Remove hack in mmap randomize
layout') as hack is no more needed since commit 8a0a9bd4db63.

So the present patch removes the comment and the hack around
get_random_int() on AArch64's mmap_rnd().

Cc: David S. Miller <davem@davemloft.net>
Cc: Anton Blanchard <anton@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Dan McGee <dpmcgee@gmail.com>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 83c3df2cb16276d120d7674cb3e9c22b0d313d4b..1bb487528a7772ba808c21cb979a9173170f53a2 100644 (file)
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -54,11 +54,12 @@ static unsigned long mmap_rnd(void)
        if (current->flags & PF_RANDOMIZE) {
 #ifdef CONFIG_COMPAT
                if (test_thread_flag(TIF_32BIT))
-                       rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
+                       rnd = get_random_long() & (1UL << mmap_rnd_compat_bits);
                else
 #endif
-                       rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
+                       rnd = get_random_long() & (1UL << mmap_rnd_bits);
        }
+
        return rnd << PAGE_SHIFT;
 }