linux-kernel - Re: [PATCH 4/6] kexec: A new system call, kexec_file

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Date:	Fri, 20 Dec 2013 15:20:16 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Torsten Duwe <duwe@....de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Greg KH <greg@...ah.com>, LKML <linux-kernel@...r.kernel.org>,
	kexec@...ts.infradead.org, "H. Peter Anvin" <hpa@...or.com>,
	Peter Jones <pjones@...hat.com>
Subject: Re: [PATCH 4/6] kexec: A new system call, kexec_file_load, for in
 kernel kexec

On Fri, Dec 20, 2013 at 3:11 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Vivek Goyal <vgoyal@...hat.com> writes:
>
>> On Thu, Dec 19, 2013 at 01:54:39PM +0100, Torsten Duwe wrote:
>>> On Tue, Nov 26, 2013 at 09:27:59AM -0500, Vivek Goyal wrote:
>
>>> IMO it's up to user land to search lists of certificates, and present
>>> only the final chain of trust to the kernel for checking.
>>>
>>> ELF is the preferred format for most sane OSes and firmware, and a detached
>>> signature would probably be simplest to check. If we have the choice,
>>> without restrictions from braindead boot loaders, ELF should be first.
>>> And if the pesigning isn't usable and another sig is needed anyway,
>>> why not apply that to vmlinux(.gz) ?
>>
>> I have yet to look deeper into it that if we can sign elf images and
>> just use elf loader. And can use space extract the elf image out of
>> a bzImage and pass it to kernel.
>>
>> Even if it is doable, one disadvantage seemed to be that extracted
>> elf images will have to be written to a file so thta it's file descriptor
>> can be passed to kernel. And that assumed writable root and we chrome
>> folks seems to have setups where root is not writable.
>
> In that case the chrome folks would simply have to use an ELF format
> kernel and not a bzImage.

If we're doing fd origin verification (not signatures), can't we
continue to use a regular bzImage?

-Kees

-- 
Kees Cook
Chrome OS Security
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