diff options
| author | dcashman <dcashman@google.com> | 2015-12-29 15:07:17 -0800 |
|---|---|---|
| committer | Moyster <oysterized@gmail.com> | 2016-09-10 16:51:12 +0200 |
| commit | 53d1ed7798ca6200040c0052121efbafe1874594 (patch) | |
| tree | 90cc505af314bec890a994f1a4292dc454dd6194 /arch | |
| parent | bd4cf354cc5f4a7c5c64b5bae1f6167423ae39c2 (diff) | |
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: Daniel Cashman <dcashman@android.com>
Signed-off-by: Daniel Cashman <dcashman@google.com>
Change-Id: I89c23a8737c981116a67381c241fdd5556e2b043
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm/Kconfig | 9 | ||||
| -rw-r--r-- | arch/arm/mm/mmap.c | 3 |
2 files changed, 10 insertions, 2 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index a2ad72521..f6de5b921 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -24,6 +24,7 @@ config ARM select HARDIRQS_SW_RESEND 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 select HAVE_ARCH_TRACEHOOK select HAVE_BPF_JIT @@ -282,6 +283,14 @@ 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. diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c index 5ef506c6f..2761c8613 100644 --- a/arch/arm/mm/mmap.c +++ b/arch/arm/mm/mmap.c @@ -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; |