> 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?
