From: Jarkko Sakkinen <jarkko@kernel.org>
To: Eric Snowberg <eric.snowberg@oracle.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
David Howells <dhowells@redhat.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,
James.Bottomley@hansenpartnership.com
Subject: Re: [PATCH v4] certs: Add EFI_CERT_X509_GUID support for dbx entries
Date: Wed, 20 Jan 2021 13:26:35 +0200 [thread overview]
Message-ID: <YAgTawk3EENF/P6j@kernel.org> (raw)
In-Reply-To: <CFBF6AEC-2832-44F7-9D7F-F20489498C33@oracle.com>
On Fri, Jan 15, 2021 at 09:49:02AM -0700, Eric Snowberg wrote:
>
> > On Jan 15, 2021, at 2:15 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >
> > On Wed, Jan 13, 2021 at 05:11:10PM -0700, Eric Snowberg wrote:
> >>
> >>> On Jan 13, 2021, at 1:41 PM, Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> >>>
> >>> 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?
> >>
> >> Today, DB and MOK certs go into the platform keyring. These certs are only
> >> referenced during kexec. They can’t be used for other things like validating
> >> kernel module signatures. If we follow the same pattern, the DBX and MOKX entries
> >> in the blacklist keyring should only impact kexec.
> >>
> >> Currently, Mickaël Salaün has another outstanding series to allow root to update
> >> the blacklist keyring. I assume the use case for this is around certificates used
> >> within the kernel, for example revoking kernel module signatures. The question I have
> >> is, should another keyring be introduced? One that carries DBX and MOKX, which just
> >> correspond to certs/hashes in the platform keyring; this keyring would only be
> >> referenced for kexec, just like the platform keyring is today. Then, the current
> >> blacklist keyring would be used for everything internal to the kernel.
> >
> > Right, I'm following actively that series.
> >
> > Why couldn't user space drive this process and use that feature to do it?
>
> I could see where the user would want to use both. With Mickaël Salaün’s
> series, the blacklist keyring is updated immediately. However it does
> not survive a reboot. With my patch, the blacklist keyring is updated
> during boot, based on what is in the dbx. Neither approach needs a new
> kernel build.
I don't want to purposely challenge this, but why does it matter
that it doesn't survive the boot? I'm referring here to the golden
principle of kernel defining a mechanism, not policy. User space
can do the population however it wants to for every boot.
E.g. systemd service could do this.
What am I missing here?
/Jarkko
next prev parent reply other threads:[~2021-01-20 12:00 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-16 0:49 [PATCH v4] certs: Add EFI_CERT_X509_GUID support for dbx entries Eric Snowberg
2020-09-16 18:09 ` Jarkko Sakkinen
2020-12-10 9:49 ` David Howells
2020-12-10 18:56 ` Eric Snowberg
2021-01-12 14:57 ` David Howells
2021-01-13 20:41 ` Jarkko Sakkinen
2021-01-14 0:11 ` Eric Snowberg
2021-01-15 9:15 ` Jarkko Sakkinen
2021-01-15 16:49 ` Eric Snowberg
2021-01-20 11:26 ` Jarkko Sakkinen [this message]
2021-01-20 22:13 ` Eric Snowberg
2021-01-21 0:36 ` Jarkko Sakkinen
2021-01-27 11:46 ` David Howells
2021-01-27 14:03 ` Mimi Zohar
2021-01-27 15:41 ` Eric Snowberg
2021-01-28 4:13 ` Nayna
2021-01-30 10:24 ` Jarkko Sakkinen
2021-01-29 23:27 ` Jarkko Sakkinen
2021-01-12 17:10 ` David Howells
2021-01-12 19:13 ` Eric Snowberg
2021-01-15 17:21 ` James Bottomley
2021-01-15 23:01 ` Eric Snowberg
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