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

Jarkko Sakkinen
2019-01-20T16:02:17Z

On Fri, Jan 18, 2019 at 12:59:06PM -0800, James Bottomley wrote:
> On Fri, 2019-01-18 at 16:33 +0200, Jarkko Sakkinen wrote:
> > 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?
>
> Because the requested functionality was a key that would be accessible
> to the kernel and not to user space and also guaranteed created by the
> kernel. The only discriminator we have to enforce that is the locality
> (assuming we reserve a locality as accessible to the kernel but
> inaccessible to userspace). PCRs alone can't restrict where the key is
> accessed or created from.

OK, locality would probably make sense, assuming that the key is stored
in nvram.

/Jarkko

/Jarkko