Re: [PATCH v4] certs: Add EFI_CERT_X509_GUID support for dbx entries

Eric Snowberg [off-list ref] wrote:

quoted

On Dec 10, 2020, at 2:49 AM, David Howells [off-list ref] wrote:

Eric Snowberg [off-list ref] wrote:

quoted

Add support for EFI_CERT_X509_GUID dbx entries. When a EFI_CERT_X509_GUID
is found, it is added as an asymmetrical key to the .blacklist keyring.
Anytime the .platform keyring is used, the keys in the .blacklist keyring
are referenced, if a matching key is found, the key will be rejected.

Ummm...  Why this way and not as a blacklist key which takes up less space?
I'm guessing that you're using the key chain matching logic.  We really only
need to blacklist the key IDs.

I implemented it this way so that certs in the dbx would only impact 
the .platform keyring. I was under the impression we didn’t want to have 
Secure Boot UEFI db/dbx certs dictate keyring functionality within the kernel
itself. Meaning if we have a matching dbx cert in any other keyring (builtin,
secondary, ima, etc.), it would be allowed. If that is not how you’d like to 
see it done, let me know and I’ll make the change.

I wonder if that is that the right thing to do.  I guess this is a policy
decision and may depend on the particular user.

quoted

Also, what should happen if a revocation cert rejected by the blacklist?

I’m not sure I understand the question. How would it be rejected?

The SHA256 of a revocation cert being loaded could match an
already-blacklisted SHA256 sum, either compiled in or already loaded from
UEFI.

David