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

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Message-Id: <87twfunneg.fsf@linux.vnet.ibm.com>
Date:	Wed, 13 Jul 2016 14:59:51 +1000
From:	Stewart Smith <stewart@...ux.vnet.ibm.com>
To:	Russell King - ARM Linux <linux@...linux.org.uk>,
	Petr Tesarik <ptesarik@...e.cz>
Cc:	linux-arm-kernel@...ts.infradead.org, bhe@...hat.com,
	arnd@...db.de, 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>,
	dyoung@...hat.com, vgoyal@...hat.com
Subject: Re: [RFC 0/3] extend kexec_file_load system call

Russell King - ARM Linux <linux@...linux.org.uk> writes:
> On Tue, Jul 12, 2016 at 10:58:05PM +0200, Petr Tesarik wrote:
>> I'm not an expert on DTB, so I can't provide an example of code
>> execution, but you have already mentioned the /chosen/linux,stdout-path
>> property. If an attacker redirects the bootloader to an insecure
>> console, they may get access to the system that would otherwise be
>> impossible.
>
> I fail to see how kexec connects with the boot loader - the DTB image
> that's being talked about is one which is passed from the currently
> running kernel to the to-be-kexec'd kernel.  For ARM (and I suspect
> also ARM64) that's a direct call chain which doesn't involve any
> boot loader or firmware, and certainly none that would involve the
> passed DTB image.

For OpenPOWER machines, kexec is the bootloader. Our bootloader is a
linux kernel and initramfs with a UI (petitboot) - this means we never
have to write a device driver twice: write a kernel one and you're done
(for booting from the device and using it in your OS).

-- 
Stewart Smith
OPAL Architect, IBM.