On Thu, 2017-04-20 at 14:36:20 UTC, Michael Ellerman wrote: > Add powerpc support for mmap_rnd_bits and mmap_rnd_compat_bits, which are two > sysctls that allow a user to configure the number of bits of randomness used > for > ASLR. > > Because of the way the Kconfig for ARCH_MMAP_RND_BITS is defined, we have to > construct at least the MIN value in Kconfig, vs in a header which would be > more > natural. Given that we just go ahead and do it all in Kconfig. > > At least according to the code (the documentation makes no mention of it), the > value is defined as the number of bits of randomisation *of the page*, not the > address. This makes some sense, with larger page sizes more of the low bits > are > forced to zero, which would reduce the randomisation if we didn't take the > PAGE_SIZE into account. However it does mean the min/max values have to change > depending on the PAGE_SIZE in order to actually limit the amount of address > space consumed by the randomisation. > > The result of that is that we have to define the default values based on both > 32-bit vs 64-bit, but also the configured PAGE_SIZE. Furthermore now that we > have 128TB address space support on Book3S, we also have to take that into > account. > > Finally we can wire up the value in arch_mmap_rnd(). > > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > Signed-off-by: Bhupesh Sharma <bhsha...@redhat.com> > Reviewed-by: Kees Cook <keesc...@chromium.org> > Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
Applied to powerpc next. https://git.kernel.org/powerpc/c/9fea59bd7ca541e5d0851f0b6dbca8 cheers
