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From:   David Howells <dhowells@redhat.com>
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References: <E090372C-06A3-4991-8FC3-F06A0DA60729@oracle.com> <20200916004927.64276-1-eric.snowberg@oracle.com> <1360578.1607593748@warthog.procyon.org.uk>
To:     Eric Snowberg <eric.snowberg@oracle.com>
Cc:     dhowells@redhat.com, dwmw2@infradead.org,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        herbert@gondor.apana.org.au, davem@davemloft.net,
        jmorris@namei.org, serge@hallyn.com, nayna@linux.ibm.com,
        Mimi Zohar <zohar@linux.ibm.com>, erichte@linux.ibm.com,
        mpe@ellerman.id.au, keyrings@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        linux-security-module@vger.kernel.org
Subject: Re: [PATCH v4] certs: Add EFI_CERT_X509_GUID support for dbx entries
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Date:   Tue, 12 Jan 2021 14:57:39 +0000
Message-ID: <2442460.1610463459@warthog.procyon.org.uk>
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Eric Snowberg <eric.snowberg@oracle.com> wrote:

> > On Dec 10, 2020, at 2:49 AM, David Howells <dhowells@redhat.com> wrote:
> >=20
> > Eric Snowberg <eric.snowberg@oracle.com> wrote:
> >=20
> >> Add support for EFI_CERT_X509_GUID dbx entries. When a EFI_CERT_X509_G=
UID
> >> is found, it is added as an asymmetrical key to the .blacklist keyring.
> >> Anytime the .platform keyring is used, the keys in the .blacklist keyr=
ing
> >> are referenced, if a matching key is found, the key will be rejected.
> >=20
> > Ummm...  Why this way and not as a blacklist key which takes up less sp=
ace?
> > I'm guessing that you're using the key chain matching logic.  We really=
 only
> > need to blacklist the key IDs.
>=20
> I implemented it this way so that certs in the dbx would only impact=20
> the .platform keyring. I was under the impression we didn=E2=80=99t want =
to have=20
> Secure Boot UEFI db/dbx certs dictate keyring functionality within the ke=
rnel
> itself. Meaning if we have a matching dbx cert in any other keyring (buil=
tin,
> secondary, ima, etc.), it would be allowed. If that is not how you=E2=80=
=99d like to=20
> see it done, let me know and I=E2=80=99ll 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.

> > Also, what should happen if a revocation cert rejected by the blacklist?
>=20
> I=E2=80=99m 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