Hi everyone,
Here is followup after the Dan's community call we had weeks ago.
Our (AMD) goal at the moment is TDISP to pass through SRIOV VFs to
confidential VMs without trusting the HV and with enabled IDE
(encryption) and IOMMU (performance, compared to current SWIOTLB). I am
aware of other uses and vendors and I spend hours unsuccessfully trying
to generalize all this in a meaningful way.
The AMD SEV TIO verbs can be simplified as:
- device_connect - starts CMA/SPDM session, returns measurements/certs,
runs IDE_KM to program the keys;
- device_reclaim - undo the connect;
- tdi_bind - transition the TDI to TDISP's LOCKED and RUN states,
generates interface report;
- tdi_unbind - undo the bind;
- tdi_info - read measurements/certs/interface report;
- tdi_validate - unlock TDI's MMIO and IOMMU (or invalidate, depends on
the parameters).
The first 4 called by the host OS, the last two by the TVM ("Trusted
VM"). These are implemented in the AMD PSP (platform processor).
There are CMA/SPDM, IDE_KV, TDISP in use.
Now, my strawman code does this on the host (I simplified a bit):
- after PCI discovery but before probing: walk through all TDISP-capable
(TEE-IO in PCIe caps) endpoint devices and call device_connect;
- when drivers probe - it is all set up and the device measurements are
visible to the driver;
- when constructing a TVM, tdi_bind is called;
and then in the TVM:
- after PCI discovery but before probing: walk through all TDIs (which
will have TEE IO bit set) and call tdi_info, verify the report, if ok -
call tdi_validate;
- when drivers probe - it is all set up and the driver decides if/which
DMA mode to use (SWIOTLB or direct), or panic().
Uff. Too long already. Sorry. Now, go to the problems:
If the user wants only CMA/SPDM, the Lukas'es patched will do that
without the PSP. This may co-exist with the AMD PSP (if the endpoint
allows multiple sessions).
If the user wants only IDE, the AMD PSP's device_connect needs to be
called and the host OS does not get to know the IDE keys. Other vendors
allow programming IDE keys to the RC on the baremetal, and this also may
co-exist with a TSM running outside of Linux - the host still manages
trafic classes and streams.
If the user wants TDISP for VMs, this assumes the user does not trust
the host OS and therefore the TSM (which is trusted) has to do CMA/SPDM
and IDE.
The TSM code is not Linux and not shared among vendors. CMA/SPDM and IDE
seem capable of co-existing, TDISP does not.
However there are common bits.
- certificates/measurements/reports blobs: storing, presenting to the
userspace (results of device_connect and tdi_bind);
- place where we want to authenticate the device and enable IDE
(device_connect);
- place where we want to bind TDI to a TVM (tdi_bind).
I've tried to address this with my (poorly named)
drivers/pci/pcie/tdisp.ko and a hack for VFIO PCI device to call tdi_bind.
The next steps:
- expose blobs via configfs (like Dan did configfs-tsm);
- s/tdisp.ko/coco.ko/;
- ask the audience - what is missing to make it reusable for other
vendors and uses?
Thanks,
--
Alexey
