Re: [Qemu-devel] vNVRAM / blobstore design

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

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 <stefanb@linux.vnet.ibm.com> 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
>>
>