linux-kernel - Re: [PATCH v4] certs: Add EFI_CERT_X509

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Date:   Fri, 15 Jan 2021 16:01:00 -0700
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     David Howells <dhowells@...hat.com>, dwmw2@...radead.org,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        jmorris@...ei.org, serge@...lyn.com, nayna@...ux.ibm.com,
        Mimi Zohar <zohar@...ux.ibm.com>, erichte@...ux.ibm.com,
        mpe@...erman.id.au, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v4] certs: Add EFI_CERT_X509_GUID support for dbx entries


> On Jan 15, 2021, at 10:21 AM, James Bottomley <James.Bottomley@...senPartnership.com> wrote:
> 
> On Tue, 2020-09-15 at 20:49 -0400, Eric Snowberg wrote:
>> The Secure Boot Forbidden Signature Database, dbx, contains a list of
>> now revoked signatures and keys previously approved to boot with UEFI
>> Secure Boot enabled.  The dbx is capable of containing any number of
>> EFI_CERT_X509_SHA256_GUID, EFI_CERT_SHA256_GUID, and
>> EFI_CERT_X509_GUID entries.
>> 
>> Currently when EFI_CERT_X509_GUID are contained in the dbx, the
>> entries are skipped.
>> 
>> 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.
>> 
>> Signed-off-by: Eric Snowberg <eric.snowberg@...cle.com>
> 
> If you're using shim, as most of our users are, you have no access to
> dbx to blacklist certificates.  Plus our security envelope includes the
> Mok variables, so you should also be paying attestion to MokListX (or
> it's RT equivalent: MokListXRT).
> 
> If you add this to the patch, we get something that is mechanistically
> complete and which also allows users to add certs to their Mok
> blacklist.

That make sense. I’ll work on a patch to add this ability.