On Wed, Oct 10, 2018 at 6:36 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > While SLAB_FREELIST_RANDOM reduces the predictability of some local slab > caches it leaves vast bulk of memory to be predictably in order > allocated. That ordering can be detected by a memory side-cache. > > The shuffling is done in terms of CONFIG_SHUFFLE_PAGE_ORDER sized free > pages where the default CONFIG_SHUFFLE_PAGE_ORDER is MAX_ORDER-1 i.e. > 10, 4MB this trades off randomization granularity for time spent > shuffling. MAX_ORDER-1 was chosen to be minimally invasive to the page > allocator while still showing memory-side cache behavior improvements, > and the expectation that the security implications of finer granularity > randomization is mitigated by CONFIG_SLAB_FREELIST_RANDOM. Perhaps it would help some of the detractors of this feature to make this a runtime choice? Some benchmarks show improvements, some show regressions. It could just be up to the admin to turn this on/off given their paranoia levels? (i.e. the shuffling could become a no-op with a given specific boot param?) -Kees -- Kees Cook Pixel Security
