On Wed, 25 Nov 2015 11:07:09 -0800 Daniel Cashman <dcashman@xxxxxxxxxxx> wrote: > On 11/24/2015 04:39 PM, Andrew Morton wrote: > > > mips, powerpc and s390 also implement arch_mmap_rnd(). Are there any > > special considerations here, or it just a matter of maintainers wiring > > it up and testing it? > > I had not yet looked at those at all, as I had no way to do even a > rudimentary "does it boot" test and opted to post v3 first. Upon first > glance, it should just be a matter of wiring it up: > > Mips is divided into 12/16 bits for 32/64 bit (assume baseline 4k page) > w/COMPAT kconfig, powerpc is 11/18 w/COMPAT, s390 is 11/11 w/COMPAT. > s390 is a bit strange as COMPAT is for a 31-bit address space, although > is_32bit_task() is used to determine which mask to use, and the mask > itself for 64-bit only introduces 11 bits of entropy, but while still > affecting larger chunks of the address space (mask is 0x3ff80, resulting > in an effective 0x7ff shift of PAGE_SIZE + 7 bits). s390 uses a mmap randomization of 11 bits but applies it to different bits dependent if the task is a compat task or not. From the machine perspective we would like to always use the randomization bits for normal, non-compat tasks. But as the 2GB address space for compat tasks is really limited the randomization is applied in bits 2^12..2^22 for compat tasks vs 2^19..2^29 for normal tasks at the cost of performance. This has to do with the cache aliasing on z13. By the way we will replace is_32bit_task with() is_compat_task(), I have a patch from Heiko pending for that. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
