From d51891f0fd12b5ad52bc9056933132f2b24f3407 Mon Sep 17 00:00:00 2001 From: dcashman Date: Tue, 12 Jan 2016 09:51:16 -0800 Subject: [PATCH] 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: Ic38735a8de2943843a73b5c20855ccfa92513422 --- arch/x86/Kconfig | 16 ++++++++++++++++ arch/x86/mm/mmap.c | 12 ++++++------ 2 files changed, 22 insertions(+), 6 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index db3622f22b61..ae3c83e8bde8 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -46,6 +46,8 @@ config X86 select ARCH_WANTS_DYNAMIC_TASK_STRUCT select ARCH_WANT_FRAME_POINTERS select ARCH_WANT_IPC_PARSE_VERSION if X86_32 + select HAVE_ARCH_MMAP_RND_BITS if MMU + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT select ARCH_WANT_OPTIONAL_GPIOLIB select BUILDTIME_EXTABLE_SORT select CLKEVT_I8253 @@ -183,6 +185,20 @@ config HAVE_LATENCYTOP_SUPPORT config MMU def_bool 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 844b06d67df4..96bd1e2bffaf 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void) { unsigned long rnd; - /* - * 8 bits of randomness in 32bit mmaps, 20 address space bits - * 28 bits of randomness in 64bit mmaps, 40 address space bits - */ if (mmap_is_ia32()) - rnd = (unsigned long)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 = (unsigned long)get_random_int() % (1<<28); + rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1); return rnd << PAGE_SHIFT; } -- 2.34.1