linux-kernel - Re: [PATCH v7 1/3] mm: Shuffle initial free memory to improve memory-side-cache utilization

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Message-ID: <CAGXu5jL1sivv70_Uahbg=cMZP2UM=eYBn4u8nx3NU5ayzHf28g@mail.gmail.com>
Date:   Thu, 10 Jan 2019 14:52:29 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Mel Gorman <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Keith Busch <keith.busch@...el.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/3] mm: Shuffle initial free memory to improve
 memory-side-cache utilization

On Thu, Jan 10, 2019 at 1:29 PM Dan Williams <dan.j.williams@...el.com> wrote:
> Note that higher order merging is not a current concern since the
> implementation is already randomizing on MAX_ORDER sized pages. Since
> memory side caches are so large there's no worry about a 4MB
> randomization boundary.
>
> However, for the (unproven) security use case where folks want to
> experiment with randomizing on smaller granularity, they should be
> wary of this (/me nudges Kees).

Yup. And I think this is well noted in the Kconfig help already. I
view this as slightly more fine grain randomization than we get from
just effectively the base address randomization that
CONFIG_RANDOMIZE_MEMORY performs.

I remain a fan of this series. :)

-- 
Kees Cook