"Kevin O'Connor" kevin@koconnor.net wrote on 08/27/2014 07:00:23 PM:
On Wed, Aug 27, 2014 at 05:04:51PM -0400, Stefan Berger wrote:
On 08/27/2014 12:26 PM, Kevin O'Connor wrote:
On Wed, Aug 27, 2014 at 09:51:02AM +0200, Gerd Hoffmann wrote:
Same applies here. IMO it should be possible to manage the TPM
without
having to touch the virtual machine configuration. Persistent
storage
isn't an issue in that case, the tpm device provides that.
Realistically, though, who is ever going to manage their TPM? Perhaps I'm missing an important use case. If so, Stefan, maybe you can describe some real-world scenarios.
The above scenario with a user having forgotten the password or a
machine
being handed off to another user where the previous user did not give
up
ownership of the TPM. In these cases the user would manage the TPM via
the
BIOS in so far as he would have to give up the TPM ownership (under
physical
presence) which is typically done in a TPM BIOS menu item.
There'stypically
also another option in the BIOS and that is one to activate / enable
the
device, maybe as one menu item or as two. Some people may want to
leave it
off, others may want to turn it on and the BIOS menu gives them this
option.
You seem to be describing two use cases: 1 - the tpm password must be reset (eg, because it was forgotten or the machine was given away/sold), and 2 - some people have a TPM chip but don't want it being used. I understand these two use cases and agree it would be worthwhile to provide a solution for them.
However, I don't think an additional SeaBIOS boot menu is a good solution for the above two use cases. By my estimation, in real world use, the above actions would likely come up only once every few years (if ever) for a given machine. Prompting the user on every boot for such a rare case is not a good complexity vs utility trade off.
Are there other use cases to consider, or am I misunderstanding the frequency of the above cases?
These are probably rare events.
To expand on my earlier proposal, lets take the second use case - a user that does not want the tpm chip being used. This decision is a machine hardware decision and I think it is something that fits well in fw_cfg/cbfs. I could see a setting "etc/tpm-state" with a value of 0 = TPM is forced to disabled, deactivated, and unowned, and a value of 1 = TPM is forced to enabled, activated, and ownable. This allows the user to set a control policy (for the next and subsequent boots) via either their virt manager (qemu) or flash tools (coreboot). This method also indirectly addresses the first use case (password reset) by the two part sequence of disabling the tpm, rebooting, then reenabling the tpm (if desired) and rebooting. Sure, it's slightly more work for the user to reset the password, but for an action that happens so rarely I don't see it as a problem.
:-/ Once we push these operations to the outside of the VM, we'll need to propagate it through all the management software (if we decided to support it there then). It runs into QEMU monitor, libvirt API and virsh management tool, virt-manager, and every cloud stack that is out there needs support in its cloud controller and on the cloud mgmt. software on the host where the VM is located (and where libvirt is) and in its API, GUI, and its own CLI tools where users will control the VM's TPM from home. All this effort would be required for an operation that is rare but not 'contained' anymore, though should be there for correctness and completeness reasons.
A TPM menu in the BIOS is probably implemented in all of today's
machines
where users expect to adjust those parameters. I would say it's almost expected to find the possibility to do this in the BIOS and those
who are used
to it would probably get more confused if it wasn't implemented
this way. This
of course doesn't preclude additional ways to support TPM management.
SeaBIOS doesn't have a system configuration menu though. On QEMU the system config menu is in the virt manager and on coreboot it's in various OS tools.
There's another spec form TCG that requires the implementation of ACPI support with the possibility to send messages to the ACPI interface indicating what to do upon reboot. It seems like this ACPI offers an API and could write these messages (operations) into the TPM's NVRAM (ACPI programs the memory mapped IO of the TPM TIS interface as it seems) that the BIOS could then look at and act upon. Maybe that would be the spec to follow and 'contain' the problem to the inside of the VM. I did use some of those ideas already when the user chosen menu item was translate in an 'operation code'.
The reserved NVRAM index of the TPM for this purpose is 0x50010000. It would be easy to read the message (1 byte) from that position from the TPM's NVRAM via the BIOS. Access is basically by sending a TPM request to the TIS interface for reading data from this special NVRAM location. The more challenging part is the ACPI program that now needs to write a similar packet to the TIS interface to write the 1 byte operation code into that NVRAM location
http://www.trustedcomputinggroup.org/files/resource_files/353F514C-1A4B-B294...
Stefan