linux-kernel - Re: [RFC] Second attempt at kernel secure boot support

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Date:	Thu, 01 Nov 2012 14:42:15 +0000
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Eric Paris <eparis@...isplace.org>
Cc:	Jiri Kosina <jkosina@...e.cz>, Oliver Neukum <oneukum@...e.de>,
	Chris Friesen <chris.friesen@...band.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Josh Boyer <jwboyer@...il.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org
Subject: Re: [RFC] Second attempt at kernel secure boot support

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@...senpartnership.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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