Re: [Qemu-devel] vNVRAM / blobstore design

[Corey Bryant]

On 03/27/2013 11:17 AM, Corey Bryant wrote:
> On 03/25/2013 06:20 PM, Stefan Berger wrote:
> > On 03/25/2013 06:05 PM, Anthony Liguori wrote:
> > > Stefan Berger <address@hidden> writes:
> > >
> > > > [argh, just posted this to qemu-trivial -- it's not trivial]
> > > >
> > > >
> > > > Hello!
> > > >
> > > > I am posting this message to revive the previous discussions about the
> > > > design of vNVRAM / blobstore cc'ing (at least) those that participated
> > > > in this discussion 'back then'.
> > > >
> > > > The first goal of the implementation is to provide an vNVRAM storage
> > > > for
> > > > a software implementation of a TPM to store its different blobs into.
> > > > Some of the data that the TPM writes into persistent memory needs to
> > > > survive a power down / power up cycle of a virtual machine, therefore
> > > > this type of persistent storage is needed. For the vNVRAM not to become
> > > > a road-block for VM migration, we would make use of block device
> > > > migration and layer the vNVRAM on top of the block device, therefore
> > > > using virtual machine images for storing the vNVRAM data.
> > > >
> > > > Besides the TPM blobs the vNVRAM should of course also be able able to
> > > > accommodate other use cases where persistent data is stored into
> > > > NVRAM,
> > > Well let's focus more on the "blob store".  What are the semantics of
> > > this?  Is there a max number of blobs?  Are the sizes fixed or variable?
> > > How often are new blobs added/removed?
>
> The max number of blobs and frequency of usage depends on the usage
> scenario and NVRAM size.  But that's probably obvious.
>
> I think we should focus on worst case scenarios where NVRAM is filled up
> and used frequently.
>
> One example is that an application can use TSS APIs to define, undefine,
> read, and write to the TPM's NVRAM storage.  (The TPM owner password is
> required to define NVRAM data.)  An application could potentially fill
> up NVRAM and frequently store, change, retrieve data in various places
> within NVRAM.  And the data could have various sizes.
>
> For an example of total NVRAM size, Infineon's TPM has 16K of NVRAM.
>
> --
> Regards,
> Corey Bryant

I just wanted to add that we could really use some direction on which 
way the community would prefer we go with this.  The 2 options that are 
on the table at the moment for encoding/decoding the vNVRAM byte stream 
are BER or JSON visitors.

--
Regards,
Corey Bryant

> > In case of TPM 1.2 there are 3 blobs that can be written at different
> > times for different reasons.
> >
> > Examples: As with a real-world TPM users loading an owner-evict key into
> > the TPM will cause the TPM to write that owner-evict key into is own
> > NVRAM. This key survives a power-off of the machine. Further, the TPM
> > models its own NVRAM slots. Someone writing into this type of memory
> > will cause data to be written into the NVRAM. There are other commands
> > that the TPM offers that will cause data to be written into NVRAM which
> > users can invoke at any time.
> >
> > The sizes of the NVRAM blobs of the TPM at least vary in size but I
> > handle this in the TPM emulation to pad them to fixed size. Depending on
> > how many such owner-evict keys are loaded into the TPM its permanent
> > state blob size may vary. Other devices may act differently.
> >
> > We have a-priori knowledge about  the 3 different types of blobs the TPM
> > device produces. They are 'registered' once at the beginning (see API)
> > and are not 'removed' as such.
> >
> > Regards,
> >      Stefan