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

[Eric Snowberg]

> On Aug 23, 2021, at 11:35 AM, Jarkko Sakkinen <jarkko at 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]?

https://lore.kernel.org/lkml/1556221605.24945.3.camel@HansenPartnership.com/