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

Jarkko Sakkinen
2021-08-23T17:36:01Z

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?

/Jarkko