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

[Kees Cook]

On Thu, Jun 29, 2017 at 10:56 AM, Tycho Andersen <tycho@xxxxxxxxxx> wrote:
> On Thu, Jun 29, 2017 at 01:54:13PM -0400, Rik van Riel wrote:
>> On Thu, 2017-06-29 at 10:47 -0700, Kees Cook wrote:
>> > On Thu, Jun 29, 2017 at 10:05 AM, Christoph Lameter <cl@xxxxxxxxx>
>> > 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.
>
> Indeed, I believe we would enable this in our kernels.

Andrew and Christoph,

What do you think about carrying this for -mm, since people are
interested in it and it's a very narrow change behind a config (with a
large impact on reducing the expoitability of freelist pointer
overwrites)?

-Kees

-- 
Kees Cook
Pixel Security