On Wed, Jan 20, 2021 at 03:13:11PM -0700, Eric Snowberg wrote: > > > On Jan 20, 2021, at 4:26 AM, Jarkko Sakkinen <jarkko@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx> wrote: > >>>>> > >>>>> On Tue, Jan 12, 2021 at 02:57:39PM +0000, David Howells wrote: > >>>>>> Eric Snowberg <eric.snowberg@xxxxxxxxxx> wrote: > >>>>>> > >>>>>>>> On Dec 10, 2020, at 2:49 AM, David Howells <dhowells@xxxxxxxxxx> wrote: > >>>>>>>> > >>>>>>>> Eric Snowberg <eric.snowberg@xxxxxxxxxx> 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
