lkml.org 
[lkml]   [2018]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v4 1/3] mm: Shuffle initial free memory
On Wed, Oct 10, 2018 at 6:36 PM, Dan Williams <dan.j.williams@intel.com> 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

\
 
 \ /
  Last update: 2018-10-16 00:26    [W:0.049 / U:12.412 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site