linux-kernel - Re: Trusted kernel patchset for Secure Boot lockdown

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Date:	Fri, 14 Mar 2014 21:58:54 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Matthew Garrett <matthew.garrett@...ula.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"jwboyer@...oraproject.org" <jwboyer@...oraproject.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: Trusted kernel patchset for Secure Boot lockdown

On Fri, 14 Mar 2014 19:24:55 +0000
Matthew Garrett <matthew.garrett@...ula.com> wrote:

> On Fri, 2014-03-14 at 14:11 -0400, Matthew Garrett wrote:
> 
> > The fact that you keep saying measured really does make me suspect that
> > you misunderstand the problem. There's no measurement involved, there's
> > simply an assertion that the firmware (which you're forced to trust)
> > chose, via some policy you may be unaware of, to trust the booted
> > kernel.
> 
> As an example, imagine a platform with the bootloader and kernel on
> read-only media. The platform can assert that the kernel is trusted even
> if there's no measurement of the kernel.

Only if you have a secure signed path through the controller firmware and
physical security of the hardware. If not I can reprogram your BIOS, your
GPU firmware, your USB stick or your CD-ROM controller to lie.

Anything must either be measurable or tamperproof from within the system
itself (or both). So a physically write protected ROM bootloader loading
a kernel and initrd from that same physically protected ROM is secure,
but your average CD-ROM drive is not.

Alan
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