From bfb69c912b280fdf56fcf2c26d8fc996cabc9f87 Mon Sep 17 00:00:00 2001 From: dcashman Date: Tue, 29 Dec 2015 15:44:12 -0800 Subject: FROMLIST: x86: mm: support ARCH_MMAP_RND_BITS. (cherry picked from commit https://lkml.org/lkml/2015/12/21/339) x86: arch_mmap_rnd() uses hard-coded values, 8 for 32-bit and 28 for 64-bit, 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: Daniel Cashman Signed-off-by: Daniel Cashman Change-Id: Id1fb53df5fedc909b79f3d952f120e6104900f24 --- arch/x86/Kconfig | 16 ++++++++++++++++ arch/x86/mm/mmap.c | 12 ++++++------ 2 files changed, 22 insertions(+), 6 deletions(-) (limited to 'arch') diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 90bf314..383c7f9 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -70,6 +70,8 @@ config X86 select IRQ_FORCED_THREADING select USE_GENERIC_SMP_HELPERS if SMP select HAVE_BPF_JIT if (X86_64 && NET) + select HAVE_ARCH_MMAP_RND_BITS if MMU + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT config INSTRUCTION_DECODER def_bool (KPROBES || PERF_EVENTS) @@ -119,6 +121,20 @@ config ZONE_DMA If unsure, say Y. +config ARCH_MMAP_RND_BITS_MIN + default 28 if 64BIT + default 8 + +config ARCH_MMAP_RND_BITS_MAX + default 32 if 64BIT + default 16 + +config ARCH_MMAP_RND_COMPAT_BITS_MIN + default 8 + +config ARCH_MMAP_RND_COMPAT_BITS_MAX + default 16 + config SBUS bool diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c index f927429..88bd010 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -81,15 +81,15 @@ static unsigned long mmap_rnd(void) { unsigned long rnd = 0; - /* - * 8 bits of randomness in 32bit mmaps, 20 address space bits - * 28 bits of randomness in 64bit mmaps, 40 address space bits - */ if (current->flags & PF_RANDOMIZE) { if (mmap_is_ia32()) - rnd = get_random_int() % (1<<8); +#ifdef CONFIG_COMPAT + rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_compat_bits) - 1); +#else + rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1); +#endif else - rnd = get_random_int() % (1<<28); + rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1); } return rnd << PAGE_SHIFT; } -- cgit v1.1