On Wed, 2021-09-08 at 16:25 -0600, Eric Snowberg wrote:

quoted

On Sep 8, 2021, at 10:49 AM, Jarkko Sakkinen [off-list ref] wrote:

On Wed, 2021-09-08 at 19:03 +0300, Jarkko Sakkinen wrote:

quoted

quoted

Downstream Linux distros try to have a single signed kernel for each
architecture.  Each end-user may use this kernel in entirely different
ways.  Some downstream kernels have chosen to always trust platform keys
within the Linux trust boundary for kernel module signing.  These
kernels have no way of using digital signature base IMA appraisal.

This series introduces a new Linux kernel keyring containing the Machine
Owner Keys (MOK) called .machine. It also adds a new MOK variable to shim.
This variable allows the end-user to decide if they want to trust keys
enrolled in the MOK within the Linux trust boundary.  By default,
nothing changes; MOK keys are not trusted within the Linux kernel.  They
are only trusted after the end-user makes the decision themselves.  The
end-user would set this through mokutil using a new --trust-mok option
[3]. This would work similar to how the kernel uses MOK variables to
enable/disable signature validation as well as use/ignore the db.

OK, changes are described here (again speaking about trusting tho). The
motivation part is missing. The text before this is more like confusion
part. When you describe motivation to do something you should really be in
grass roots, e.g. "when you have this feature in the kernel, look, I can
do now this". It's not that hard. E.g. with an usage example it is quite
quick accomplish this.

The code changes overally make sense but this motivotional part is the
problem. E.g. if you do a pull request, it is completely *unusable* in
that context. In that case I would have to write something that should
have been the cover letter. It's 12 patches, so it is perfectly sensible
to ask a better one.

Would this be a more appropriate cover letter that includes a better
motivation?

Back in 2013 Linus requested a feature to allow end-users to have the 
ability "to add their own keys and sign modules they trust".  This was his 
*second* order outlined here [1].  There have been many attempts over the
years to solve this problem, all have been rejected.  Many distributions 
carry one of these rejected attempts. This series tries to solve this problem 
with a solution that takes into account all the problems brought up in the 
previous attempts.

Instead of making the reviewer look up the failed attempts, please
summarize why they failed (e.g. all preboot firmware keys were
trusted), and then continue, like below, with how this attempt differs.

This series introduces a new Linux kernel keyring containing the Machine
Owner Keys (MOK) called .machine.

Other archs will also want to allow loading "end-users" key.  Please
prefix this paragraph with something like "On UEFI based systems".

 It also adds a new MOK variable to shim.

Replace "adds" with "defines".

This variable allows the end-user to decide if they want to load keys
enrolled in the MOK within the Linux kernel.  By default, nothing changes; 
MOK keys are not loaded within the Linux kernel.  They are only loaded after
the end-user makes the decision themselves.  The end-user would set this 
through mokutil using a new --trust-mok option [2]. This would work similar 
to how the kernel uses MOK variables to enable/disable signature validation 
as well as use/ignore the db. Mimi has suggested that only CA keys be loaded 
into this keyring. All other certs will load into the platform keyring instead.

Thank you for crediting me for limiting loading only the CA keys stored
in the MOK db onto the "machine" keyring, but the limitation should be
better integrated in the paragraph.

Secure Boot keys will never be loaded.  They will always be loaded into
the platform keyring.  If an end-user wanted to load one, they would
need to enroll it into the MOK.

Steps required by the end user:

Sign kernel module with user created key:
$ /usr/src/kernels/$(uname -r)/scripts/sign-file sha512 signing_key.priv \
    signing_key.x509 my_module.ko

Import the key into the MOK
$ mokutil --import signing_key.x509

To differentiate this "signing_key" from others, perhaps name the file
"machine_sigining_key" or "local_signing_key".

thanks,

Mimi

Setup the kernel to load MOK keys into the .machine keyring
$ mokutil —trust-mok

Then reboot, the MokManager will load and ask if you want to trust the MOK 
key and enroll the MOK into the MOKList.  Afterwards the signed kernel module 
will load.

I have included links to both the mokutil [2] and shim [3] changes I
have made to support this new functionality.

[1] https://marc.info/?l=linux-kernel&m=136185386310140&w=2
[2] https://github.com/esnowberg/mokutil/tree/0.3.0-mokvars-v2
[3] https://github.com/esnowberg/shim/tree/mokvars-v2