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Date: Wed, 9 Dec 2015 16:41:04 -0800
From: Kees Cook <>
To: "" <>
Subject: Re: Self Introduction

On Wed, Dec 9, 2015 at 4:26 PM, David Brown <> wrote:
> On Wed, Dec 09, 2015 at 04:14:20PM -0800, Kees Cook wrote:
>> Great! It might be valuable to read through this mailing lists's
>> threads over the last month. We discuss a few of the features and some
>> work has been started.
> Reading through stuff now.  Looks like the list got quite a boost in
> November.
>>> I suspect part of the challenge is going to be clearly describing the
>>> various features along with specific examples of already-discovered
>>> exploits that the feature would have mitigated.
>> Yes indeed. :) That's why I've arranged the wiki the way I did:
>> classes and methods first, with potential solutions listed under them.
>> We want to start with problem descriptions and work from actual
>> exploits when possible.
>> This is why the recent x86 VDSO attack was very timely: it
>> demonstrates cleanly why we want __ro_after_init (née __read_only) in
>> upstream. (As well as the constification plugin.)
> Which also seems like this will be quite useful on ARM as well.  Do
> you know any efforts to do this?

I've not seen any yet. If you get it written, I can include it in my
__ro_after_init series on the next revision.

>>> Most recently, I backported ARM PAN support to the Linaro stable
>>> kernels (3.18 and 4.1).
>> Excellent! Yes, I did a port to Brillo's v4.1 tree as well. It's very
>> nice to have a UDEREF-like feature on arm. It's too bad this doesn't
>> exist for Intel yet, but I'm hoping they'll step up.
>> For 3.18, is this the right place to be looking?
> It will be once it gets through testing.
> to peek before then.  There's also
> for the 4.1 tree.

Oh! I see now. You meant hardware PAN support. Yes, also good to get
in for the arm64 devices. I meant the CONFIG_CPU_SW_DOMAIN_PAN
support. I've backported that from 4.3 to 4.1 since then all arm
devices would gain PAN-like support too.

> Should I CC kernel-hardening when sending patches for the Linaro
> stable kernels?

Probably not for stable backports. I think upstream development things
probably should be, and we can certainly discuss stuff that looks like
it'd be good to backport, but I wouldn't want to bore people with
patch for old kernels. :)

>> I'd love to see CONFIG_CPU_SW_DOMAIN_PAN into the AOSP 3.18 android kernel
>> too.
> I'll put this on my list to investigate.  Sadly, it looks like there
> is a bit of a window of ARM CPUs where neither solution will work;
> Basically the pre V8.1 64-bit.

The LPAE support for PAN emulation exists in grsecurity, if someone
wanted to look at how to extract it and add it to

> In fact, I don't have any hardware yet that supports PAN.  I've done
> all of the testing in emulation.

Heh, yeah, that's how the x86 SMAP stuff is too. ;)


Kees Cook
Chrome OS & Brillo Security

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