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? 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. cheers -- 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>