[PATCH 0/7] Add CA enforcement keyring restrictions

[Eric Snowberg]

> On Nov 8, 2022, at 6:24 PM, Elaine Palmer <erpalmerny at gmail.com> wrote:
> 
> 
> 
> On 2022/11/04 9:20 AM, Coiby Xu wrote:
>> Hi Eric,
>> 
>> I wonder if there is any update on this work? I would be glad to do
>> anything that may be helpful including testing a new version of code.
>> 
> Hi Coiby,
> 
> Yes, this discussion got stuck when we couldn't agree on one of the
> following options:
> 
> (A) Filter which keys from MOK (or a management system) are loaded
>     onto the .machine keyring. Specifically, load only keys with
>     CA+keyCertSign attributes.
> 
> (B) Load all keys from MOK (or a management system) onto the
>     .machine keyring. Then, subsequently filter those to restrict
>     which ones can be loaded onto the .ima keyring specifically.
> 
> The objection to (A) was that distros would have to go through
> two steps instead of one to load keys. The one-step method of
> loading keys was supported by an out-of-tree patch and then by
> the addition of the .machine keyring.
> 
> The objection to (B) was that, because the .machine keyring is now
> linked to the .secondary keyring, it expands the scope of what the
> kernel has trusted in the past. The effect is that keys in MOK
> have the same broad scope as keys previously restricted to
> .builtin and .secondary. It doesn't affect just IMA, but the rest
> of the kernel as well.
> 
> I would suggest that we can get unstuck by considering:
> 
> (C) Defining a systemd (or dracut module) to load keys onto the
>     .secondary keyring
> 
> (D) Using a configuration option to specify what types of
>     .machine keys should be allowed to pass through to the
>     .secondary keyring.
>    
>     The distro could choose (A) by allowing only
>     CA+keyCertSign keys.
> 
>     The distro could choose (B) by allowing any kind
>     of key.
> 
> We all seemed to agree that enforcing key usage should be
> implemented and that a useful future effort is to add policies
> to keys and keyrings, like, "This key can only be used for
> verifying kernel modules."
> 
> I hope we can come to an agreement so work can proceed and IMA
> can be re-enabled.

I would be open to making the changes necessary to support both (A and B) 
options.  What type of configuration option would be considered?  Would this 
be a compile time Kconfig, a Linux boot command line parameter, or another 
MOK variable?