linux-kernel - Re: [PATCH v4 1/3] mm: Shuffle initial free memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20181016111230.GR18839@dhcp22.suse.cz>
Date:   Tue, 16 Oct 2018 13:12:30 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] mm: Shuffle initial free memory

On Mon 15-10-18 15:25:47, Kees Cook wrote:
> On Wed, Oct 10, 2018 at 6:36 PM, Dan Williams <dan.j.williams@...el.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?)

Sure, making this a opt-in is really necessary but it would be even
_better_ to actually evaluate how much security relevance it has as
well. If for nothing else then to allow an educated decision rather than
a fear driven one. And that pretty much involves evaluation on how hard
it is to bypass the randomness. If I am going to pay some overhead I
would like to know how much hardening I get in return, right? Something
completely missing in the current evaluation so far.
-- 
Michal Hocko
SUSE Labs