Re: [PATCH 00/12] One more attempt at useful kernel lockdown

Kees Cook
2013-09-10T18:55:53Z

On Tue, Sep 10, 2013 at 11:51 AM, gregkh@linuxfoundation.org
<gregkh@linuxfoundation.org> wrote:
> On Tue, Sep 10, 2013 at 11:29:45AM -0700, H. Peter Anvin wrote:
>> On 09/10/2013 11:26 AM, Matthew Garrett wrote:
>> > On Tue, 2013-09-10 at 14:23 -0300, Henrique de Moraes Holschuh wrote:
>> >> On Tue, 10 Sep 2013, Matthew Garrett wrote:
>> >>> That's why modern systems require signed firmware updates.
>> >>
>> >> Linux doesn't. Is someone working on adding signature support to the
>> >> runtime firmware loader?
>> >
>> > It'd be simple to do so, but so far the model appears to be that devices
>> > that expect signed firmware enforce that themselves.
>> >
>>
>> Most devices do absolutely no verification on the firmware, and simply
>> trust the driver.
>>
>> So signing firmware is probably critical.
>
> How are you going to "validate" that the firmware is correct, given
> that it's just a "blob" living in the linux-firmware tree. If you sign
> it, what is that saying?

In theory these blobs are traceable to a manufacturer. It's not really
an indication that it's "safe" more than it's an indication that it
hasn't been changed. But I haven't chased this very hard yet because
of below...

> I'm with Matthew here, any device that needs/wants this, has their own
> built-in checking, nothing the kernel should do here.
>
> Especially given that no other os does this :)

Yeah, it's impossible to handle since the way components do firmware
updates is frequently exposed to userspace anyway. 3G modems that do
firmware updates over the AT-command set, harddrives doing firmware
updates over SCSI-generic commands, etc. Creating this barrier in the
kernel is not a good solution; the component makers need to be doing
the enforcement. :(

-Kees

--
Kees Cook
Chrome OS Security