Re: [PATCH 1/5 v2] PM / hibernate: Create snapshot keys handler

Jarkko Sakkinen
2019-01-18T14:35:05Z

On Fri, Jan 11, 2019 at 07:28:58AM -0800, James Bottomley wrote:
> On Fri, 2019-01-11 at 16:02 +0200, Jarkko Sakkinen wrote:
> > On Tue, Jan 08, 2019 at 05:43:53PM -0800, Andy Lutomirski wrote:
> > > (Also, do we have a sensible story of how the TPM interacts with
> > > hibernation at all? Presumably we should at least try to replay
> > > the PCR operations that have occurred so that we can massage the
> > > PCRs into the same state post-hibernation. Also, do we have any
> > > way for the kernel to sign something with the TPM along with an
> > > attestation that the signature was requested *by the
> > > kernel*? Something like a sub-hierarchy of keys that the kernel
> > > explicitly prevents userspace from accessing?)
> >
> > Kernel can keep it is own key hierarchy in memory as TPM2 chips allow
> > to offload data in encrypted form and load it to TPM when it needs to
> > use it.
> >
> > The in-kernel resource manager that I initiated couple years ago
> > provides this type of functionality.
>
> Actually, the resource manager only keeps volatile objects separated
> when in use not when offloaded. The problem here is that the object
> needs to be persisted across reboots, so either it gets written to the
> NV area, bypassing the resource manager and making it globally visible
> or it has to get stored in TPM form in the hibernation image, meaning
> anyone with access to the TPM who can read the image can extract and
> load it. Further: anyone with access to the TPM can create a bogus
> sealed key and encrypt a malicious hibernation image with it. So there
> are two additional problems
>
> 1. Given that the attacker may have access to the binary form of the
> key, can we make sure only the kernel can get it released?
> 2. How do we prevent an attacker with access to the TPM from creating a
> bogus sealed key?
>
> This is why I was thinking localities.

Why you would want to go for localities and not seal to PCRs?

/Jarkko