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SubjectRe: [RFC] Second attempt at kernel secure boot support
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On Thu, 2012-11-01 at 10:29 -0400, Eric Paris wrote:
> On Thu, Nov 1, 2012 at 5:59 AM, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
>
> > But that doesn't really help me: untrusted root is an oxymoron.
>
> Imagine you run windows and you've never heard of Linux. You like
> that only windows kernels can boot on your box and not those mean
> nasty hacked up malware kernels. Now some attacker manages to take
> over your box because you clicked on that executable for young models
> in skimpy bathing suits. That executable rewrote your bootloader to
> launch a very small carefully crafted Linux environment. This
> environment does nothing but launch a perfectly valid signed Linux
> kernel, which gets a Windows environment all ready to launch after
> resume and goes to sleep. Now you have to hit the power button twice
> every time you turn on your computer, weird, but Windows comes up, and
> secureboot is still on, so you must be safe!

So you're going back to the root exploit problem? I thought that was
debunked a few emails ago in the thread?

Your attack vector isn't plausible because for the suspend attack to
work, the box actually has to be running Linux by default ... I think
the admin of that box might notice if it suddenly started running
windows ...

> In this case we have a completely 'untrusted' root inside Linux. From
> the user PoV root and Linux are both malware. Notice the EXACT same
> attack would work launching rootkit'd Linux from Linux. So don't
> pretend not to care about Windows. It's just that launching malware
> Linux seems like a reason to get your key revoked. We don't want
> signed code which can be used as an attack vector on ourselves or on
> others.
>
> That make sense?

Not really, no. A windows attack vector is a pointless abstraction
because we're talking about securing Linux and your vector requires a
Linux attack for the windows compromise ... let's try to keep on point
to how we're using this feature to secure Linux.

James




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