On 11/24/2015 08:40 PM, Michael Ellerman wrote: > On Wed, 2015-11-18 at 15:20 -0800, Daniel Cashman wrote: > >> From: dcashman <dcashman@xxxxxxxxxx> >> >> ASLR currently only uses 8 bits to generate the random offset for the >> mmap base address on 32 bit architectures. This value was chosen to >> prevent a poorly chosen value from dividing the address space in such >> a way as to prevent large allocations. This may not be an issue on all >> platforms. Allow the specification of a minimum number of bits so that >> platforms desiring greater ASLR protection may determine where to place >> the trade-off. > > ... > >> diff --git a/arch/Kconfig b/arch/Kconfig >> index 4e949e5..141823f 100644 >> --- a/arch/Kconfig >> +++ b/arch/Kconfig >> @@ -511,6 +511,70 @@ config ARCH_HAS_ELF_RANDOMIZE >> - arch_mmap_rnd() >> - arch_randomize_brk() >> >> +config HAVE_ARCH_MMAP_RND_BITS >> + bool >> + help >> + An arch should select this symbol if it supports setting a variable >> + number of bits for use in establishing the base address for mmap >> + allocations and provides values for both: >> + - ARCH_MMAP_RND_BITS_MIN >> + - ARCH_MMAP_RND_BITS_MAX >> + >> +config ARCH_MMAP_RND_BITS_MIN >> + int >> + >> +config ARCH_MMAP_RND_BITS_MAX >> + int >> + >> +config ARCH_MMAP_RND_BITS_DEFAULT >> + int >> + >> +config ARCH_MMAP_RND_BITS >> + int "Number of bits to use for ASLR of mmap base address" if EXPERT >> + range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX >> + default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT > > Here you support a default which is separate from the minimum. > >> + default ARCH_MMAP_RND_BITS_MIN >> + depends on HAVE_ARCH_MMAP_RND_BITS > > ... >> + >> +config ARCH_MMAP_RND_COMPAT_BITS >> + int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT >> + range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX >> + default ARCH_MMAP_RND_COMPAT_BITS_MIN > > But here you don't. > > Just forgot? Yes. Good catch. > I'd like to have a default which is separate from the minimum. That way we can > have a default which is reasonably large, but allow it to be lowered easily if > anything breaks. Will add it, along w/the documentation cleanup and other changes. Thank You, Dan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>