Messages in this thread | | | Date | Sun, 20 Jan 2019 18:02:04 +0200 | From | Jarkko Sakkinen <> | Subject | Re: [PATCH 1/5 v2] PM / hibernate: Create snapshot keys handler |
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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
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