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

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Message-ID: <20121101144912.GA10269@srcf.ucam.org>
Date:	Thu, 1 Nov 2012 14:49:12 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Eric Paris <eparis@...isplace.org>, Jiri Kosina <jkosina@...e.cz>,
	Oliver Neukum <oneukum@...e.de>,
	Chris Friesen <chris.friesen@...band.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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, Nov 01, 2012 at 02:42:15PM +0000, James Bottomley wrote:
> On Thu, 2012-11-01 at 10:29 -0400, Eric Paris wrote:
> > 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?

The entire point of this feature is that it's no longer possible to turn 
a privileged user exploit into a full system exploit. Gaining admin 
access on Windows 8 doesn't permit you to install a persistent backdoor, 
unless there's some way to circumvent that. Which there is, if you can 
drop a small Linux distribution onto the ESP and use a signed, trusted 
bootloader to boot a signed, trusted kernel that then resumes from an 
unsigned, untrusted hibernate image. So we have to ensure that that's 
impossible.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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