linux-kernel - Re: [PATCH 02/11] libnvdimm/security: change clear text nvdimm keys to encrypted keys

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Date:   Sun, 11 Nov 2018 15:09:35 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Dave Jiang <dave.jiang@...el.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        keyrings@...r.kernel.org
Subject: Re: [PATCH 02/11] libnvdimm/security: change clear text nvdimm keys
 to encrypted keys

> > Traditionally there is a single master key for the system, which would
> > be sealed to a set of boot time PCR values.  After decrypting all of
> > the encrypted keys, the master key would be removed from the keyring
> > and a PCR extended.  Extending a PCR would prevent the master key from
> > being unsealed again and used to decrypt encrypted keys, without
> > rebooting the system.  Normally this would be done before pivoting
> > root.
> >
> > If you're not referring to the system master key and are intentionally
> > limiting usage to TPM 2.0, more details on the master key security
> > requirements should be included.
> 
> Oh, interesting point. I think we had been assuming a local +
> unsealed-at-runtime nvdimm master key rather than a system-wide master
> key. Yes, we need to rethink this in terms of supporting a sealed
> system-key. This would seem to limit security actions, outside of
> unlock, to always requiring a reboot. I.e. the nominal case is that we
> boot up and unlock the DIMMs, but any subsequent security operation
> like erase, or change-passphrase would require rebooting into an
> environment where the system-master key is unsealed. I do think
> re-provisioning keys and erasing DIMM contents are sufficiently
> exceptional events that a reboot requirement is tolerable.

> Is there already existing tooling around this to be able to schedule
> master-key related actions to be deferred to an initrd environment?

There's the original dracut support for loading a masterkey, which is
used by the EVM and ecryptfs dracut modules.  After the last usage,
the masterkey needs to be removed from the keyring.

Different people over the years have wanted to add support for
calculating the boot time expected PCRs values in order to reseal keys
(trusted key update), but I haven't looked to see if there are any
open source tools available.

Mimi