Re: [PATCH 9/9] MODSIGN: Allow the "db" UEFI variable to be suppressed

Ard Biesheuvel
2016-11-21T16:42:49Z

On 21 November 2016 at 16:26, Josh Boyer <jwboyer@fedoraproject.org> wrote:
> On Mon, Nov 21, 2016 at 11:18 AM, Ard Biesheuvel
> <ard.biesheuvel@linaro.org> wrote:
>> On 16 November 2016 at 18:11, David Howells <dhowells@redhat.com> wrote:
>>> From: Josh Boyer <jwboyer@fedoraproject.org>
>>>
>>> If a user tells shim to not use the certs/hashes in the UEFI db variable
>>> for verification purposes, shim will set a UEFI variable called
>>> MokIgnoreDB. Have the uefi import code look for this and ignore the db
>>> variable if it is found.
>>>
>>
>> Similar concern as in the previous patch: it appears to me that you
>> can DoS a machine by setting MokIgnoreDB if, e.g., its modules are
>> signed against a cert that resides in db, and shim/mokmanager are not
>> being used.
>
> If shim/mokmanager aren't used, then you can't actually modify
> MokIgnoreDB. Again, it requires physical access and a reboot into
> mokmanager to actually take effect.
>

This does the trick as well

printf "\x07\x00\x00\x00\x01" >
/sys/firmware/efi/efivars/MokIgnoreDB-605dab50-e046-4300-abb6-3dd810dd8b23