Re: [PATCH v4 00/12] Enroll kernel keys thru MOK

Eric Snowberg
2021-08-23T17:49:13Z

> On Aug 23, 2021, at 11:35 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
>
> On Thu, 2021-08-19 at 09:10 -0400, Mimi Zohar wrote:
>> On Thu, 2021-08-19 at 14:38 +0300, Jarkko Sakkinen wrote:
>>> On Wed, 2021-08-18 at 20:20 -0400, Eric Snowberg wrote:
>>>> Many UEFI Linux distributions boot using shim. The UEFI shim provides
>>>> what is called Machine Owner Keys (MOK). Shim uses both the UEFI Secure
>>>> Boot DB and MOK keys to validate the next step in the boot chain. The
>>>> MOK facility can be used to import user generated keys. These keys can
>>>> be used to sign an end-user development kernel build. When Linux boots,
>>>> pre-boot keys (both UEFI Secure Boot DB and MOK keys) get loaded in the
>>>> Linux .platform keyring.
>>>>
>>>> Currently, pre-boot keys are not trusted within the Linux trust boundary
>>>> [1]. These platform keys can only be used for kexec. If an end-user
>>>> wants to use their own key within the Linux trust boundary, they must
>>>> either compile it into the kernel themselves or use the insert-sys-cert
>>>> script. Both options present a problem. Many end-users do not want to
>>>> compile their own kernels. With the insert-sys-cert option, there are
>>>> missing upstream changes [2]. Also, with the insert-sys-cert option,
>>>> the end-user must re-sign their kernel again with their own key, and
>>>> then insert that key into the MOK db. Another problem with
>>>> insert-sys-cert is that only a single key can be inserted into a
>>>> compressed kernel.
>>>>
>>>> Having the ability to insert a key into the Linux trust boundary opens
>>>> up various possibilities. The end-user can use a pre-built kernel and
>>>> sign their own kernel modules. It also opens up the ability for an
>>>> end-user to more easily use digital signature based IMA-appraisal. To
>>>> get a key into the ima keyring, it must be signed by a key within the
>>>> Linux trust boundary.
>>>
>>> As of today, I can use a prebuilt kernel, crate my own MOK key and sign
>>> modules. What will be different?
>>
>> The UEFI db and MOK keys are being loaded onto the .platform keyring,
>> which is suppose to be limited to verifying the kexec kernel image
>> signature. With a downstream patch, kernel modules are being verified
>> as well.
>>
>> Initially Patrick Uiterwijk's "[PATCH 0/3] Load keys from TPM2 NV Index
>> on IMA keyring" patch set attempted to define a new root of trust based
>> on a key stored in the TPM. This patch set is similarly attempting to
>> define a new root of trust based on CA keys stored in the MOK db.
>>
>> The purpose of this patch set is to define a new, safe trust source
>> parallel to the builtin keyring, without relying on a downstream patch.
>> With the new root of trust, the end user could sign his own kernel
>> modules, sign third party keys, and load keys onto the IMA keyring,
>> which can be used for signing the IMA policy and other files.
>
> I can, as of today, generate my own mok key and sign my LKM's, and
> kernel will verify my LKM's.
>
> What is different?

Are you sure your kernel doesn’t contain some version of the rejected
patch referenced in the cover letter [1]?