linux-kernel - Re: [RFC 0/3] extend kexec_file

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Message-ID: <20160715134209.GF1041@n2100.armlinux.org.uk>
Date:	Fri, 15 Jul 2016 14:42:10 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Arnd Bergmann <arnd@...db.de>, Mark Rutland <mark.rutland@....com>,
	Stewart Smith <stewart@...ux.vnet.ibm.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>, bhe@...hat.com,
	linuxppc-dev@...ts.ozlabs.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	AKASHI Takahiro <takahiro.akashi@...aro.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
	Samuel Mendoza-Jonas <sam@...dozajonas.com>,
	Dave Young <dyoung@...hat.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 0/3] extend kexec_file_load system call

On Fri, Jul 15, 2016 at 09:26:10AM -0400, Vivek Goyal wrote:
> On Fri, Jul 15, 2016 at 09:31:02AM +0200, Arnd Bergmann wrote:
> > I think that helps, as it makes the problem space correspond to that
> > of modifying the command line, but I can still come up with countless
> > attacks based on modifications of the /chosen node and/or the command
> > line, in fact it's probably easier than any other node.
> 
> I don't know anything about DTB. So here comes a very basic question. Does
> DTB allow passing an executable blob to kernel or pass the location of
> some unsigned executable code at kernel level.

DT on ARM is a description of the hardware - it can be thought of as a
set of nodes with properties attached.  The properties can describe
anything (we have documentation in Documentation/devicetree/bindings
which describes what we expect the properties to contain.)

On other architectures, DT can also contain open-firmware "functions"
but I don't think there's much support in the kernel for that - maybe
the PPC folk can reply on that point.

It is possible that someone may, at some point, decide to create a
property that points to some executable blob, but I can't think of a
reason why we should ever allow such a monstrosity in mainline kernels.

-- 
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