On 8/30/21 1:39 PM, Eric Snowberg wrote:
On Aug 27, 2021, at 2:44 PM, Nayna <nayna@xxxxxxxxxxxxxxxxxx> wrote:
On 8/25/21 6:27 PM, James Bottomley wrote:
Remember, a CA cert is a self signed cert with the CA:TRUE basic
constraint. Pretty much no secure boot key satisfies this (secure boot
chose deliberately NOT to use CA certificates, so they're all some type
of intermediate or leaf), so the design seems to be only to pick out
the CA certificates you put in the MOK keyring. Adding the _ca suffix
may deflect some of the "why aren't all my MOK certificates in the
keyring" emails ...
My understanding is the .system_ca keyring should not be restricted only
to self-signed CAs (Root CA). Any cert that can qualify as Root or
Intermediate CA with Basic Constraints CA:TRUE should be allowed. In
fact, the intermediate CA certificates closest to the leaf nodes would be
best.
With an intermediate containing CA:TRUE, the intermediate cert would not
be self signed. Just for my clarification, does this mean I should remove
the check that validates if it is self signed and instead somehow check if
the CA flag is set? Wouldn’t this potentially allow improperly signed certs
into this new keyring?
In this model, we are relying on the admin to ensure the authenticity of
the certificate(s) being loaded onto the new keyring. It is similar to
trusting the admin to enable the variable and add keys to MOK. Following
are the checks that must pass before adding it to .system_ca keyring.
1. Check against revocation_list.
2. Check Basic Constraints: CA=TRUE.
3. Check keyUsage = keyCertSign.
Thanks & Regards,
- Nayna
