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

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Message-Id: <87k2gqndyx.fsf@linux.vnet.ibm.com>
Date:	Wed, 13 Jul 2016 18:23:34 +1000
From:	Stewart Smith <stewart@...ux.vnet.ibm.com>
To:	Arnd Bergmann <arnd@...db.de>, linuxppc-dev@...ts.ozlabs.org
Cc:	Mark Rutland <mark.rutland@....com>, bhe@...hat.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Vivek Goyal <vgoyal@...hat.com>,
	AKASHI Takahiro <takahiro.akashi@...aro.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	bauerman@...ux.vnet.ibm.com, Dave Young <dyoung@...hat.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 0/3] extend kexec_file_load system call

Arnd Bergmann <arnd@...db.de> writes:
> On Wednesday, July 13, 2016 10:36:14 AM CEST Dave Young wrote:
>> On 07/12/16 at 03:50pm, Mark Rutland wrote:
>> > On Tue, Jul 12, 2016 at 04:24:10PM +0200, Arnd Bergmann wrote:
>> > > On Tuesday, July 12, 2016 10:18:11 AM CEST Vivek Goyal wrote:
>> > 
>> > /proc/devicetree (aka /sys/firmware/devicetree) is a filesystem derived
>> > from the raw DTB (which is exposed at /sys/firmware/fdt).
>> > 
>> > The blob that was handed to the kernel at boot time is exposed at
>> > /sys/firmware/fdt.
>> 
>> I believe the blob can be read and passed to kexec kernel in kernel code without
>> the extra fd.
>> 
>> But consider we can kexec to a different kernel and a different initrd so there
>> will be use cases to pass a total different dtb as well. From my understanding
>> it is reasonable but yes I think we should think carefully about the design.
>
> Ok, I can see four interesting use cases here:
>
> - Using the dtb that the kernel has saved at boot time. Ideally this should not
>   require an additional step of signing it, since the running kernel already
>   trusts it.

- using current view of the hardware, flattened into a new dtb.
  This should already be trusted, as it's what we're running now (boot +
  runtime changes)

-- 
Stewart Smith
OPAL Architect, IBM.