[PATCH v8 16/17] integrity: Trust MOK keys if MokListTrustedRT found

[Eric Snowberg]

> On Nov 9, 2022, at 5:01 PM, Morten Linderud <morten at linderud.pw> wrote:
> 
> On Tue, Nov 23, 2021 at 11:41:23PM -0500, Eric Snowberg wrote:
>> A new Machine Owner Key (MOK) variable called MokListTrustedRT has been
>> introduced in shim. When this UEFI variable is set, it indicates the
>> end-user has made the decision themselves that they wish to trust MOK keys
>> within the Linux trust boundary.  It is not an error if this variable
>> does not exist. If it does not exist, the MOK keys should not be trusted
>> within the kernel.
> 
> Hi Eric,
> 
> I've been milling around on this patch-set for a while and I have a few issues
> with the description of the commit and what the code actually does.
> 
> efi_mokvar_entry_find doesn't simply read an UEFI variable as the commit message
> suggests, it will look for the MOK variable loaded into the EFI configuration
> table. This implies we need this table setup in early boot to take usage of this
> patch set.
> 
> The only bootloader that does setup this table, is the `shim` as described. But
> no other bootloader implements support for the MOK EFI configuration table.
> 
> This effectively means that there is still no way for Machine Owners to load
> keys into the keyring, for things like module signing, without the shim present
> in the bootchain. I find this a bit weird.
> 
> Is this an intentional design decision, or could other ways be supported as
> well?

In v6 I had it as a RT variable, during the review a request was made [1] to just 
use the EFI configuration table.  If there are other boot loaders that want to use this,
I don’t see why the code in v6 couldn’t be added back.  If the configuration table isn’t
available, it could try reading the RT var next.

1. https://patchwork.kernel.org/project/linux-integrity/patch/20210914211416.34096-13-eric.snowberg@oracle.com/#24453409