Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit d6c763af authored by Yann Droneaud's avatar Yann Droneaud Committed by Will Deacon
Browse files

arm64/mm: Remove hack in mmap randomize layout 



Since commit 8a0a9bd4 ('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
1d18c47c ('arm64: MMU fault handling and page table management')
are incorrects.

Commit 1d18c47c seems to use the same hack introduced by
commit a5adc91a ('powerpc: Ensure random space between stack
and mmaps'), latter copied in commit 5a0efea0 ('sparc64: Sharpen
address space randomization calculations.').

But both architectures were cleaned up as part of commit
fa8cbaaf ('powerpc+sparc64/mm: Remove hack in mmap randomize
layout') as hack is no more needed since commit 8a0a9bd4.

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: default avatarWill Deacon <will.deacon@arm.com>
Acked-by: default avatarDan McGee <dpmcgee@gmail.com>
Signed-off-by: default avatarYann Droneaud <ydroneaud@opteya.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 7d57511d

arch/arm64/mm/mmap.c

+2 −10
Original line number Diff line number Diff line
@@ -47,22 +47,14 @@ static int mmap_is_legacy(void) 
	return sysctl_legacy_va_layout;

}



/*

 * Since get_random_int() returns the same value within a 1 jiffy window, we

 * will almost always get the same randomisation for the stack and mmap

 * region. This will mean the relative distance between stack and mmap will be

 * the same.

 *

 * To avoid this we can shift the randomness by 1 bit.

 */

static unsigned long mmap_rnd(void)

{

	unsigned long rnd = 0;



	if (current->flags & PF_RANDOMIZE)

		rnd = (long)get_random_int() & (STACK_RND_MASK >> 1);

		rnd = (long)get_random_int() & STACK_RND_MASK;



	return rnd << (PAGE_SHIFT + 1);

	return rnd << PAGE_SHIFT;

}



static unsigned long mmap_base(void)