Commit 045d2c8d authored by dcashman's avatar dcashman Committed by mohancm100
Browse files

FROMLIST: arm: mm: support ARCH_MMAP_RND_BITS. 

(cherry picked from commit https://lkml.org/lkml/2015/12/21/341

)

arm: arch_mmap_rnd() uses a hard-code value of 8 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 8 as the minimum acceptable value.

Bug: 24047224
Signed-off-by: default avatarDaniel Cashman <dcashman@android.com>
Signed-off-by: default avatarDaniel Cashman <dcashman@google.com>
Change-Id: I0d5988d378bea2d7bf7ac8db90ddd95623a52c68
parent 51d98c01

arch/arm/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ config ARM 
	select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT)

	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL

	select HAVE_ARCH_KGDB

	select HAVE_ARCH_MMAP_RND_BITS if MMU

	select HAVE_ARCH_SECCOMP_FILTER if (AEABI && !OABI_COMPAT)

	select HAVE_ARCH_TRACEHOOK

	select HAVE_BPF_JIT
@@ -296,6 +297,14 @@ 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

	default 8



config ARCH_MMAP_RND_BITS_MAX

	default 14 if PAGE_OFFSET=0x40000000

	default 15 if PAGE_OFFSET=0x80000000

	default 16



#

# 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

+1 −2
Original line number Diff line number Diff line
@@ -173,10 +173,9 @@ 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) - 1)) << PAGE_SHIFT;



	if (mmap_is_legacy()) {

		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;