linux-kernel - Re: [PATCH 07/11] kexec: Disable in a secure boot environment

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Message-ID: <20120905154308.GA8457@mobil.systemanalysen.net>
Date:	Wed, 5 Sep 2012 17:43:08 +0200
From:	Roland Eggner <edvx1@...temanalysen.net>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org
Subject: Re: [PATCH 07/11] kexec: Disable in a secure boot environment

On 2012-09-04 Tuesday at 22:40 +0100 Matthew Garrett wrote:
> On Tue, Sep 04, 2012 at 10:39:57PM +0100, Alan Cox wrote:
> > I think it needs to be defined in terms of what the capability is
> > supposed to guarantee. I have a feeling Matthew has a pretty clear idea
> > about that in his head so can nail it fairly precisely ?
> 
> In the absence of this capability, all users (including root) should be 
> unable to cause untrusted code to be executed in ring 0. This requires 
> some straightforward and obvious conditions like "The user must not be 
> able to load untrusted modules", but also conditions like "The user must 
> not be able to cause devices to DMA over the kernel". "The user must not 
> be able to kexec into an untrusted kernel" is at the more obvious end of 
> the scale. This is obviously dependent upon there being some mechanism 
> for ensuring that the initial kernel is trusted in the first place, 
> which is where the firmware security comes in.

You believe in firmware security?  Not yet heard of “Rakshasa”?  Reading [1] may 
change your mind.

Want to support Erics technical arguments, given in another branche of this
thread, by some “political” aspects:  If I have payed for a device and then would
not be allowed to use it due to some obscure “security” feature, this could
perhaps be close to criminal.  I am not a lawyer, can only guess.  A few years ago
a friend of mine bought an originally quite expensive, used notebook for just a
few Euro.  The seller was forced to do so, just because he added RAM and changed
HD, causing activation of an unknown hardware password.  It has been set by a
retailer or the vendor, the latter being one of the largest players on the world
market.  Certainly I will never buy a device of this brand.  If Linux mainline
would really implement some kind of knock-out “security” feature, and would
switch from GPL to another, for such a new policy more adequate copyright
licence:  it would be sad, but technically no problem, there are plenty of
alternatives beyond penguins, windows and gates.  Other users and contributors
might follow … not good for the future of the Linux project.  Better stick to the
GPL and policy of freedom, then 20 years of aweful success on servers and
embedded devices are more likely to continue or even to grow.

[1]
Jonathan Brossard:  “… We have built a generic proof of concept malware for the 
Intel architecture,  called 'Rakshasa',  capable of infecting more than 100 
different motherboards.  Targets are BIOS and firmware of PCI-devices.  …”
http://www.toucan-system.com/research/blackhat2012_brossard_hardware_backdooring.pdf

-- 
Roland Eggner

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