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Signed-off-by: Leonardo Garcia <lagarcia@br.ibm.com> Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com> Message-Id: <ea1554e3a02e093eaa64d1260faf01d525c9ecdc.1642446876.git.lagarcia@br.ibm.com> Signed-off-by: Cédric Le Goater <clg@kaod.org>
90 lines
3.6 KiB
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90 lines
3.6 KiB
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===================================
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Hypervisor calls and the Ultravisor
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===================================
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On PPC64 systems supporting Protected Execution Facility (PEF), system memory
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can be placed in a secured region where only an ultravisor running in firmware
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can provide access to. pSeries guests on such systems can communicate with
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the ultravisor (via ultracalls) to switch to a secure virtual machine (SVM) mode
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where the guest's memory is relocated to this secured region, making its memory
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inaccessible to normal processes/guests running on the host.
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The various ultracalls/hypercalls relating to SVM mode are currently only
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documented internally, but are planned for direct inclusion into the Linux on
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Power Architecture Reference document ([LoPAR]_). An internal ACR has been filed
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to reserve a hypercall number range specific to this use case to avoid any
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future conflicts with the IBM internally maintained Power Architecture Platform
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Reference (PAPR+) documentation specification. This document summarizes some of
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these details as they relate to QEMU.
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Hypercalls needed by the ultravisor
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===================================
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Switching to SVM mode involves a number of hcalls issued by the ultravisor to
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the hypervisor to orchestrate the movement of guest memory to secure memory and
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various other aspects of the SVM mode. Numbers are assigned for these hcalls
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within the reserved range ``0xEF00-0xEF80``. The below documents the hcalls
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relevant to QEMU.
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``H_TPM_COMM`` (``0xef10``)
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---------------------------
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SVM file systems are encrypted using a symmetric key. This key is then
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wrapped/encrypted using the public key of a trusted system which has the private
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key stored in the system's TPM. An Ultravisor will use this hcall to
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unwrap/unseal the symmetric key using the system's TPM device or a TPM Resource
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Manager associated with the device.
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The Ultravisor sets up a separate session key with the TPM in advance during
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host system boot. All sensitive in and out values will be encrypted using the
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session key. Though the hypervisor will see the in and out buffers in raw form,
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any sensitive contents will generally be encrypted using this session key.
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Arguments:
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``r3``: ``H_TPM_COMM`` (``0xef10``)
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``r4``: ``TPM`` operation, one of:
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``TPM_COMM_OP_EXECUTE`` (``0x1``): send a request to a TPM and receive a
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response, opening a new TPM session if one has not already been opened.
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``TPM_COMM_OP_CLOSE_SESSION`` (``0x2``): close the existing TPM session, if
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any.
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``r5``: ``in_buffer``, guest physical address of buffer containing the
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request. Caller may use the same address for both request and response.
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``r6``: ``in_size``, size of the in buffer. Must be less than or equal to
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4 KB.
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``r7``: ``out_buffer``, guest physical address of buffer to store the
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response. Caller may use the same address for both request and response.
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``r8``: ``out_size``, size of the out buffer. Must be at least 4 KB, as this
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is the maximum request/response size supported by most TPM implementations,
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including the TPM Resource Manager in the linux kernel.
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Return values:
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``r3``: one of the following values:
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``H_Success``: request processed successfully.
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``H_PARAMETER``: invalid TPM operation.
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``H_P2``: ``in_buffer`` is invalid.
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``H_P3``: ``in_size`` is invalid.
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``H_P4``: ``out_buffer`` is invalid.
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``H_P5``: ``out_size`` is invalid.
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``H_RESOURCE``: problem communicating with TPM.
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``H_FUNCTION``: TPM access is not currently allowed/configured.
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``r4``: For ``TPM_COMM_OP_EXECUTE``, the size of the response will be stored
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here upon success.
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