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Date:   Wed, 13 Jan 2021 22:41:22 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     David Howells <dhowells@redhat.com>
Cc:     Eric Snowberg <eric.snowberg@oracle.com>, dwmw2@infradead.org,
        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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 <20200916004927.64276-1-eric.snowberg@oracle.com>
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On Tue, Jan 12, 2021 at 02:57:39PM +0000, David Howells wrote:
> Eric Snowberg <eric.snowberg@oracle.com> wrote:
> 
> > > On Dec 10, 2020, at 2:49 AM, David Howells <dhowells@redhat.com> wrote:
> > > 
> > > Eric Snowberg <eric.snowberg@oracle.com> wrote:
> > > 
> > >> 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.

Why would you want to allow dbx entry in any keyring?

/Jarkko