From b14c867ed7fc877f2148a67ecb729dd17f63a979 Mon Sep 17 00:00:00 2001 From: dcashman Date: Tue, 29 Dec 2015 15:07:17 -0800 Subject: [PATCH] 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 Signed-off-by: Daniel Cashman Change-Id: I2f6c18a0060e1c21b53200ecdcfde9a8c2e3db98 Signed-off-by: Kevin F. Haggerty --- arch/arm/Kconfig | 9 +++++++++ arch/arm/mm/mmap.c | 3 +-- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 388d860da77..3580f421f77 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -16,6 +16,7 @@ config ARM select HAVE_KPROBES if !XIP_KERNEL select HAVE_KRETPROBES if (HAVE_KPROBES) select HAVE_FUNCTION_TRACER if (!XIP_KERNEL) + select HAVE_ARCH_MMAP_RND_BITS if MMU select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL) select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) select HAVE_FUNCTION_GRAPH_TRACER if (!THUMB2_KERNEL) @@ -312,6 +313,14 @@ 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 1b5c90a8c02..b2acc9a9fdb 100644 --- a/arch/arm/mm/mmap.c +++ b/arch/arm/mm/mmap.c @@ -280,10 +280,9 @@ 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;