Commit 51d98c01 authored by dcashman's avatar dcashman Committed by mohancm100
Browse files

FROMLIST: arm64: mm: support ARCH_MMAP_RND_BITS. 

(cherry picked from commit https://lkml.org/lkml/2015/12/21/340

)

arm64: arch_mmap_rnd() uses STACK_RND_MASK to generate the
random offset for the mmap base address.  This value represents a
compromise between increased ASLR effectiveness and avoiding
address-space fragmentation. Replace it with a Kconfig option, which
is sensibly bounded, so that platform developers may choose where to
place this compromise. Keep default values as new minimums.

Bug: 24047224
Signed-off-by: default avatarDaniel Cashman <dcashman@android.com>
Signed-off-by: default avatarDaniel Cashman <dcashman@google.com>
Change-Id: Ie94f0068927861637414348077c7f33057bbbeb7
parent 7f9cae42

arch/arm64/Kconfig

+29 −0
Original line number Diff line number Diff line
@@ -37,6 +37,8 @@ config ARM64 
	select HAVE_ARCH_AUDITSYSCALL

	select HAVE_ARCH_JUMP_LABEL

	select HAVE_ARCH_KGDB

	select HAVE_ARCH_MMAP_RND_BITS

	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT

	select HAVE_ARCH_SECCOMP_FILTER

	select HAVE_ARCH_TRACEHOOK

	select HAVE_BPF_JIT
@@ -87,6 +89,33 @@ config ARCH_PHYS_ADDR_T_64BIT 
config MMU

	def_bool y



config ARCH_MMAP_RND_BITS_MIN

       default 14 if ARM64_64K_PAGES

       default 16 if ARM64_16K_PAGES

       default 18



# max bits determined by the following formula:

#  VA_BITS - PAGE_SHIFT - 3

config ARCH_MMAP_RND_BITS_MAX

       default 19 if ARM64_VA_BITS=36

       default 24 if ARM64_VA_BITS=39

       default 27 if ARM64_VA_BITS=42

       default 30 if ARM64_VA_BITS=47

       default 29 if ARM64_VA_BITS=48 && ARM64_64K_PAGES

       default 31 if ARM64_VA_BITS=48 && ARM64_16K_PAGES

       default 33 if ARM64_VA_BITS=48

       default 14 if ARM64_64K_PAGES

       default 16 if ARM64_16K_PAGES

       default 18



config ARCH_MMAP_RND_COMPAT_BITS_MIN

       default 7 if ARM64_64K_PAGES

       default 9 if ARM64_16K_PAGES

       default 11



config ARCH_MMAP_RND_COMPAT_BITS_MAX

       default 16



config NO_IOPORT_MAP

	def_bool y if !PCI

arch/arm64/mm/mmap.c

+9 −12
Original line number Diff line number Diff line
@@ -47,22 +47,19 @@ 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);



	return rnd << (PAGE_SHIFT + 1);

	if (current->flags & PF_RANDOMIZE) {

#ifdef CONFIG_COMPAT

		if (test_thread_flag(TIF_32BIT))

			rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_compat_bits) - 1);

		else

#endif

			rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);

	}

	return rnd << PAGE_SHIFT;

}



static unsigned long mmap_base(void)