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? /Jarkko
