Re: [Qemu-devel] [PATCH 1/2] docs/specs: initial spec summary for Ultravisor-related hcalls

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting David Gibson (2019-07-12 01:40:27)
> On Thu, Jul 11, 2019 at 08:19:33PM -0500, Michael Roth wrote:
> > 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 <mdroth@linux.vnet.ibm.com>
> 
> Thanks for adding this documentation.  Is there a PAPR extension
> proposal which covers this, which we could cite as the source?

We have an internal document/repo that serves as a catch-all for the Ultravisor
related spec changes. We could make that available publically via github and
cite it here until it hits the full spec. Would that work?

> 
> > ---
> >  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.
> 
> -- 
> David Gibson                    | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
>                                 | _way_ _around_!
> http://www.ozlabs.org/~dgibson