linux-kernel - Re: [PATCH v2] mm: Add SLUB free list pointer obfuscation

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Message-ID: <1498758853.6130.2.camel@redhat.com>
Date:   Thu, 29 Jun 2017 13:54:13 -0400
From:   Rik van Riel <riel@...hat.com>
To:     Kees Cook <keescook@...omium.org>, Christoph Lameter <cl@...ux.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Laura Abbott <labbott@...hat.com>,
        Daniel Micay <danielmicay@...il.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Tejun Heo <tj@...nel.org>, Daniel Mack <daniel@...que.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Helge Deller <deller@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2] mm: Add SLUB free list pointer obfuscation

On Thu, 2017-06-29 at 10:47 -0700, Kees Cook wrote:
> On Thu, Jun 29, 2017 at 10:05 AM, Christoph Lameter <cl@...ux.com>
> wrote:
> > On Sun, 25 Jun 2017, Kees Cook wrote:
> > 
> > > The difference gets lost in the noise, but if the above is
> > > sensible,
> > > it's 0.07% slower. ;)
> > 
> > Hmmm... These differences add up. Also in a repetative benchmark
> > like that
> > you do not see the impact that the additional cacheline use in the
> > cpu
> > cache has on larger workloads. Those may be pushed over the edge of
> > l1 or
> > l2 capacity at some point which then causes drastic regressions.
> 
> Even if that is true, it may be worth it to some people to have the
> protection. Given that is significantly hampers a large class of heap
> overflow attacks[1], I think it's an important change to have. I'm
> not
> suggesting this be on by default, it's cleanly behind
> CONFIG-controlled macros, and is very limited in scope. If you can
> Ack
> it we can let system builders decide if they want to risk a possible
> performance hit. I'm pretty sure most distros would like to have this
> protection.

I could certainly see it being useful for all kinds of portable
and network-connected systems where security is simply much
more important than performance.