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: Thu, 21 Jan 2021 02:36:43 +0200 [thread overview]
Message-ID: <YAjMm9Gq/FFOzQYG@kernel.org> (raw)
In-Reply-To: <D9F5E0BD-E2FC-428F-91B3-35D2750493A0@oracle.com>
On Wed, Jan 20, 2021 at 03:13:11PM -0700, Eric Snowberg wrote:
>
> > On Jan 20, 2021, at 4:26 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >
> > 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?
>
> This change simply adds support for a missing type. The kernel
> already supports cert and hash entries (EFI_CERT_X509_SHA256_GUID,
> EFI_CERT_SHA256_GUID) that originate from the dbx and are loaded
> into the blacklist keyring during boot. I’m not sure why a cert
> defined with EFI_CERT_X509_GUID should be handled in a different
> manner.
>
> I suppose a user space tool could be created. But wouldn’t what is
> currently done in the kernel in this area need to be removed?
Right. I don't think this was a great idea in the first place to
do to the kernel but since it exists, I guess the patch does make
sense.
/Jarkko
next prev parent reply other threads:[~2021-01-21 1:04 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
2021-01-20 22:13 ` Eric Snowberg
2021-01-21 0:36 ` Jarkko Sakkinen [this message]
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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