For now this only covers hcalls relating to TPM communication since it's the only one particularly important from a QEMU perspective atm, but others can be added here where it makes sense.
The full specification for all hcalls/ucalls will eventually be made available in the public/OpenPower version of the PAPR specification. Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com> --- docs/specs/ppc-spapr-uv-hcalls.txt | 74 ++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) create mode 100644 docs/specs/ppc-spapr-uv-hcalls.txt diff --git a/docs/specs/ppc-spapr-uv-hcalls.txt b/docs/specs/ppc-spapr-uv-hcalls.txt new file mode 100644 index 0000000000..0278f89190 --- /dev/null +++ b/docs/specs/ppc-spapr-uv-hcalls.txt @@ -0,0 +1,74 @@ +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 to access it. pseries guests on such +systems can communicate with the ultravisor (via ultracalls) to switch to a +secure VM mode (SVM) 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 +public OpenPOWER version of the PAPR specification (LoPAPR/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 internally-maintained PAPR +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 SVM mode. The below documents the hcalls +relevant to QEMU. + +- H_TPM_COMM (0xef10) + + For TPM_COMM_OP_EXECUTE operation: + Send a request to a TPM and receive a response, opening a new TPM session + if one has not already been opened. + + For TPM_COMM_OP_CLOSE_SESSION operation: + Close the existing TPM session, if any. + + Arguments: + + r3 : H_TPM_COMM (0xef10) + r4 : TPM operation, one of: + TPM_COMM_OP_EXECUTE (0x1) + TPM_COMM_OP_CLOSE_SESSION (0x2) + 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 + - Must be less than or equal to 4KB + 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 4KB, 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 : 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 TPM is unavailable + r4 : For TPM_COMM_OP_EXECUTE, the size of the response will be stored here + upon success. + + Use-case/notes: + + SVM filesystems 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. -- 2.17.1