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Commit bc8eb3ef authored by dcashman's avatar dcashman Committed by Mark Salyzyn
Browse files

arm: mm: support ARCH_MMAP_RND_BITS. 



Bug: 24047224
Signed-off-by: default avatarDaniel Cashman <dcashman@google.com>
Change-Id: Ie4b6d175f636a8ee4b25cdc0a0407d440278ff63
parent 565ef503

arch/arm/Kconfig

+24 −0
Original line number Diff line number Diff line
@@ -296,6 +296,30 @@ config MMU 
	  Select if you want MMU-based virtualised addressing space

	  support by paged memory management. If unsure, say 'Y'.



config ARCH_MMAP_RND_BITS_MIN

	int

	default 8



config ARCH_MMAP_RND_BITS_MAX

	int

	default 14 if MMU && PAGE_OFFSET=0x40000000

	default 15 if MMU && PAGE_OFFSET=0x80000000

	default 16 if MMU

	default 8



config ARCH_MMAP_RND_BITS

	int "Number of bits to use for ASLR of mmap base address" if EXPERT

	range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX

	default ARCH_MMAP_RND_BITS_MIN

	help

	  This value can be used to select the number of bits to use to

	  determine the random offset to the base address of vma regions

	  resulting from mmap allocations. This value will be bounded

	  by the architecture's minimum and maximum supported values.



	  This value can be changed after boot using the

	  /proc/sys/kernel/mmap_rnd_bits tunable



#

# The "ARM system type" choice list is ordered alphabetically by option

# text.  Please add new entries in the option alphabetic order.

arch/arm/mm/mmap.c

+5 −2
Original line number Diff line number Diff line
@@ -11,6 +11,10 @@ 
#include <linux/random.h>

#include <asm/cachetype.h>



int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;

int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;

int mmap_rnd_bits = CONFIG_ARCH_MMAP_RND_BITS;



#define COLOUR_ALIGN(addr,pgoff)		\

	((((addr)+SHMLBA-1)&~(SHMLBA-1)) +	\

	 (((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))
@@ -173,10 +177,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm) 
{

	unsigned long random_factor = 0UL;



	/* 8 bits of randomness in 20 address space bits */

	if ((current->flags & PF_RANDOMIZE) &&

	    !(current->personality & ADDR_NO_RANDOMIZE))

		random_factor = (get_random_int() % (1 << 8)) << PAGE_SHIFT;

		random_factor = (get_random_int() % (1 << mmap_rnd_bits)) << PAGE_SHIFT;



	if (mmap_is_legacy()) {

		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;