linux-kernel - Re: [PATCH] mm: Add additional consistency check

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Date:   Tue, 4 Apr 2017 17:16:00 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Christoph Lameter <cl@...ux.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Add additional consistency check

On Tue 04-04-17 10:07:23, Cristopher Lameter wrote:
> On Tue, 4 Apr 2017, Michal Hocko wrote:
> 
> > NAK without a proper changelog. Seriously, we do not blindly apply
> > changes from other projects without a deep understanding of all
> > consequences.
> 
> Functionalitywise this is trivial. A page must be a slab page in order to
> be able to determine the slab cache of an object. Its definitely not ok if
> the page is not a slab page.

Yes, but we do not have to blow the kernel, right? Why cannot we simply
leak that memory?

> The main issue that may exist here is the adding of overhead to a critical
> code path like kfree().

Yes, nothing is for free. But if the attack space is real then we
probably want to sacrifice few cycles (to simply return ASAP without
further further processing). This all should be in the changelog ideally
with some numbers. I suspect this would be hard to measure in most
workloads.

-- 
Michal Hocko
SUSE Labs