linux-kernel - Re: [PATCH 0/6] kexec: A new system call to allow in kernel loading

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Message-ID: <CAGXu5jJVskjN8YAh-QxS08CLGHgRvLq3Hdef2rg2gnxMCz_BRw@mail.gmail.com>
Date:	Fri, 22 Nov 2013 09:45:13 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kexec@...ts.infradead.org, "H. Peter Anvin" <hpa@...or.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Greg Kroah-Hartman <greg@...ah.com>
Subject: Re: [PATCH 0/6] kexec: A new system call to allow in kernel loading

On Fri, Nov 22, 2013 at 7:33 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Fri, Nov 22, 2013 at 02:50:43PM +0100, Jiri Kosina wrote:
>> On Fri, 22 Nov 2013, Vivek Goyal wrote:
>>
>> > > OTOH, does this feature make any sense whatsover on architectures that
>> > > don't support secure boot anyway?
>> >
>> > I guess if signed modules makes sense, then being able to kexec signed
>> > kernel images should make sense too, in general.
>>
>> Well, that's really a grey zone, I'd say.
>>
>> In a non-secureboot environment, if you are root, you are able to issue
>> reboot into a completely different, self-made kernel anyway, independent
>> on whether signed modules are used or not.
>
> That's a good poing. Frankly speaking I don't know if there is a good
> use case to allow loading signed kernels only or not.
>
> Kees mentioned that he would like to know where the kernel came from
> and whether it came from trusted disk or not. So he does seem to have
> a use case where he wants to launch only trusted kernel or deny execution.

Correct. Though to clarify, Chrome OS doesn't use UEFI SecureBoot: we
have a different solution that uses dm-verity to give us a trusted
read-only root filesystem. As long as things live on that filesystem,
we trust them. (This is why finit_module was added, and why I wanted
to make sure kexec used fd instead of "just" a memory blob.)

-Kees

-- 
Kees Cook
Chrome OS Security
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