90 lines
3.6 KiB
ReStructuredText
90 lines
3.6 KiB
ReStructuredText
===================================
|
|
Hypervisor calls and the Ultravisor
|
|
===================================
|
|
|
|
On PPC64 systems supporting Protected Execution Facility (PEF), system memory
|
|
can be placed in a secured region where only an ultravisor running in firmware
|
|
can provide access to. pSeries guests on such systems can communicate with
|
|
the ultravisor (via ultracalls) to switch to a secure virtual machine (SVM) mode
|
|
where the guest's memory is relocated to this secured region, making its memory
|
|
inaccessible to normal processes/guests running on the host.
|
|
|
|
The various ultracalls/hypercalls relating to SVM mode are currently only
|
|
documented internally, but are planned for direct inclusion into the Linux on
|
|
Power Architecture Reference document ([LoPAR]_). An internal ACR has been filed
|
|
to reserve a hypercall number range specific to this use case to avoid any
|
|
future conflicts with the IBM internally maintained Power Architecture Platform
|
|
Reference (PAPR+) documentation specification. This document summarizes some of
|
|
these details as they relate to QEMU.
|
|
|
|
Hypercalls needed by the ultravisor
|
|
===================================
|
|
|
|
Switching to SVM mode involves a number of hcalls issued by the ultravisor to
|
|
the hypervisor to orchestrate the movement of guest memory to secure memory and
|
|
various other aspects of the SVM mode. Numbers are assigned for these hcalls
|
|
within the reserved range ``0xEF00-0xEF80``. The below documents the hcalls
|
|
relevant to QEMU.
|
|
|
|
``H_TPM_COMM`` (``0xef10``)
|
|
---------------------------
|
|
|
|
SVM file systems are encrypted using a symmetric key. This key is then
|
|
wrapped/encrypted using the public key of a trusted system which has the private
|
|
key stored in the system's TPM. An Ultravisor will use this hcall to
|
|
unwrap/unseal the symmetric key using the system's TPM device or a TPM Resource
|
|
Manager associated with the device.
|
|
|
|
The Ultravisor sets up a separate session key with the TPM in advance during
|
|
host system boot. All sensitive in and out values will be encrypted using the
|
|
session key. Though the hypervisor will see the in and out buffers in raw form,
|
|
any sensitive contents will generally be encrypted using this session key.
|
|
|
|
Arguments:
|
|
|
|
``r3``: ``H_TPM_COMM`` (``0xef10``)
|
|
|
|
``r4``: ``TPM`` operation, one of:
|
|
|
|
``TPM_COMM_OP_EXECUTE`` (``0x1``): send a request to a TPM and receive a
|
|
response, opening a new TPM session if one has not already been opened.
|
|
|
|
``TPM_COMM_OP_CLOSE_SESSION`` (``0x2``): close the existing TPM session, if
|
|
any.
|
|
|
|
``r5``: ``in_buffer``, guest physical address of buffer containing the
|
|
request. Caller may use the same address for both request and response.
|
|
|
|
``r6``: ``in_size``, size of the in buffer. Must be less than or equal to
|
|
4 KB.
|
|
|
|
``r7``: ``out_buffer``, guest physical address of buffer to store the
|
|
response. Caller may use the same address for both request and response.
|
|
|
|
``r8``: ``out_size``, size of the out buffer. Must be at least 4 KB, as this
|
|
is the maximum request/response size supported by most TPM implementations,
|
|
including the TPM Resource Manager in the linux kernel.
|
|
|
|
Return values:
|
|
|
|
``r3``: one of the following values:
|
|
|
|
``H_Success``: request processed successfully.
|
|
|
|
``H_PARAMETER``: invalid TPM operation.
|
|
|
|
``H_P2``: ``in_buffer`` is invalid.
|
|
|
|
``H_P3``: ``in_size`` is invalid.
|
|
|
|
``H_P4``: ``out_buffer`` is invalid.
|
|
|
|
``H_P5``: ``out_size`` is invalid.
|
|
|
|
``H_RESOURCE``: problem communicating with TPM.
|
|
|
|
``H_FUNCTION``: TPM access is not currently allowed/configured.
|
|
|
|
``r4``: For ``TPM_COMM_OP_EXECUTE``, the size of the response will be stored
|
|
here upon success.
|