447 lines
15 KiB
ReStructuredText
447 lines
15 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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======================================
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Secure Encrypted Virtualization (SEV)
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======================================
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Overview
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========
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Secure Encrypted Virtualization (SEV) is a feature found on AMD processors.
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SEV is an extension to the AMD-V architecture which supports running
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virtual machines (VMs) under the control of a hypervisor. When enabled,
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the memory contents of a VM will be transparently encrypted with a key
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unique to that VM.
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The hypervisor can determine the SEV support through the CPUID
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instruction. The CPUID function 0x8000001f reports information related
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to SEV::
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0x8000001f[eax]:
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Bit[1] indicates support for SEV
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...
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[ecx]:
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Bits[31:0] Number of encrypted guests supported simultaneously
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If support for SEV is present, MSR 0xc001_0010 (MSR_AMD64_SYSCFG) and MSR 0xc001_0015
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(MSR_K7_HWCR) can be used to determine if it can be enabled::
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0xc001_0010:
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Bit[23] 1 = memory encryption can be enabled
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0 = memory encryption can not be enabled
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0xc001_0015:
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Bit[0] 1 = memory encryption can be enabled
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0 = memory encryption can not be enabled
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When SEV support is available, it can be enabled in a specific VM by
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setting the SEV bit before executing VMRUN.::
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VMCB[0x90]:
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Bit[1] 1 = SEV is enabled
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0 = SEV is disabled
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SEV hardware uses ASIDs to associate a memory encryption key with a VM.
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Hence, the ASID for the SEV-enabled guests must be from 1 to a maximum value
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defined in the CPUID 0x8000001f[ecx] field.
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SEV Key Management
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==================
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The SEV guest key management is handled by a separate processor called the AMD
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Secure Processor (AMD-SP). Firmware running inside the AMD-SP provides a secure
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key management interface to perform common hypervisor activities such as
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encrypting bootstrap code, snapshot, migrating and debugging the guest. For more
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information, see the SEV Key Management spec [api-spec]_
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The main ioctl to access SEV is KVM_MEMORY_ENCRYPT_OP. If the argument
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to KVM_MEMORY_ENCRYPT_OP is NULL, the ioctl returns 0 if SEV is enabled
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and ``ENOTTY` if it is disabled (on some older versions of Linux,
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the ioctl runs normally even with a NULL argument, and therefore will
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likely return ``EFAULT``). If non-NULL, the argument to KVM_MEMORY_ENCRYPT_OP
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must be a struct kvm_sev_cmd::
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struct kvm_sev_cmd {
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__u32 id;
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__u64 data;
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__u32 error;
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__u32 sev_fd;
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};
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The ``id`` field contains the subcommand, and the ``data`` field points to
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another struct containing arguments specific to command. The ``sev_fd``
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should point to a file descriptor that is opened on the ``/dev/sev``
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device, if needed (see individual commands).
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On output, ``error`` is zero on success, or an error code. Error codes
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are defined in ``<linux/psp-dev.h>``.
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KVM implements the following commands to support common lifecycle events of SEV
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guests, such as launching, running, snapshotting, migrating and decommissioning.
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1. KVM_SEV_INIT
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---------------
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The KVM_SEV_INIT command is used by the hypervisor to initialize the SEV platform
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context. In a typical workflow, this command should be the first command issued.
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The firmware can be initialized either by using its own non-volatile storage or
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the OS can manage the NV storage for the firmware using the module parameter
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``init_ex_path``. If the file specified by ``init_ex_path`` does not exist or
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is invalid, the OS will create or override the file with output from PSP.
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Returns: 0 on success, -negative on error
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2. KVM_SEV_LAUNCH_START
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-----------------------
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The KVM_SEV_LAUNCH_START command is used for creating the memory encryption
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context. To create the encryption context, user must provide a guest policy,
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the owner's public Diffie-Hellman (PDH) key and session information.
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Parameters: struct kvm_sev_launch_start (in/out)
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_launch_start {
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__u32 handle; /* if zero then firmware creates a new handle */
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__u32 policy; /* guest's policy */
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__u64 dh_uaddr; /* userspace address pointing to the guest owner's PDH key */
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__u32 dh_len;
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__u64 session_addr; /* userspace address which points to the guest session information */
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__u32 session_len;
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};
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On success, the 'handle' field contains a new handle and on error, a negative value.
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KVM_SEV_LAUNCH_START requires the ``sev_fd`` field to be valid.
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For more details, see SEV spec Section 6.2.
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3. KVM_SEV_LAUNCH_UPDATE_DATA
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-----------------------------
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The KVM_SEV_LAUNCH_UPDATE_DATA is used for encrypting a memory region. It also
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calculates a measurement of the memory contents. The measurement is a signature
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of the memory contents that can be sent to the guest owner as an attestation
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that the memory was encrypted correctly by the firmware.
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Parameters (in): struct kvm_sev_launch_update_data
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_launch_update {
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__u64 uaddr; /* userspace address to be encrypted (must be 16-byte aligned) */
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__u32 len; /* length of the data to be encrypted (must be 16-byte aligned) */
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};
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For more details, see SEV spec Section 6.3.
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4. KVM_SEV_LAUNCH_MEASURE
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-------------------------
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The KVM_SEV_LAUNCH_MEASURE command is used to retrieve the measurement of the
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data encrypted by the KVM_SEV_LAUNCH_UPDATE_DATA command. The guest owner may
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wait to provide the guest with confidential information until it can verify the
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measurement. Since the guest owner knows the initial contents of the guest at
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boot, the measurement can be verified by comparing it to what the guest owner
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expects.
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If len is zero on entry, the measurement blob length is written to len and
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uaddr is unused.
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Parameters (in): struct kvm_sev_launch_measure
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_launch_measure {
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__u64 uaddr; /* where to copy the measurement */
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__u32 len; /* length of measurement blob */
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};
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For more details on the measurement verification flow, see SEV spec Section 6.4.
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5. KVM_SEV_LAUNCH_FINISH
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------------------------
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After completion of the launch flow, the KVM_SEV_LAUNCH_FINISH command can be
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issued to make the guest ready for the execution.
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Returns: 0 on success, -negative on error
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6. KVM_SEV_GUEST_STATUS
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-----------------------
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The KVM_SEV_GUEST_STATUS command is used to retrieve status information about a
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SEV-enabled guest.
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Parameters (out): struct kvm_sev_guest_status
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_guest_status {
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__u32 handle; /* guest handle */
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__u32 policy; /* guest policy */
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__u8 state; /* guest state (see enum below) */
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};
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SEV guest state:
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::
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enum {
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SEV_STATE_INVALID = 0;
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SEV_STATE_LAUNCHING, /* guest is currently being launched */
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SEV_STATE_SECRET, /* guest is being launched and ready to accept the ciphertext data */
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SEV_STATE_RUNNING, /* guest is fully launched and running */
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SEV_STATE_RECEIVING, /* guest is being migrated in from another SEV machine */
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SEV_STATE_SENDING /* guest is getting migrated out to another SEV machine */
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};
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7. KVM_SEV_DBG_DECRYPT
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----------------------
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The KVM_SEV_DEBUG_DECRYPT command can be used by the hypervisor to request the
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firmware to decrypt the data at the given memory region.
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Parameters (in): struct kvm_sev_dbg
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_dbg {
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__u64 src_uaddr; /* userspace address of data to decrypt */
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__u64 dst_uaddr; /* userspace address of destination */
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__u32 len; /* length of memory region to decrypt */
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};
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The command returns an error if the guest policy does not allow debugging.
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8. KVM_SEV_DBG_ENCRYPT
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----------------------
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The KVM_SEV_DEBUG_ENCRYPT command can be used by the hypervisor to request the
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firmware to encrypt the data at the given memory region.
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Parameters (in): struct kvm_sev_dbg
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_dbg {
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__u64 src_uaddr; /* userspace address of data to encrypt */
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__u64 dst_uaddr; /* userspace address of destination */
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__u32 len; /* length of memory region to encrypt */
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};
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The command returns an error if the guest policy does not allow debugging.
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9. KVM_SEV_LAUNCH_SECRET
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------------------------
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The KVM_SEV_LAUNCH_SECRET command can be used by the hypervisor to inject secret
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data after the measurement has been validated by the guest owner.
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Parameters (in): struct kvm_sev_launch_secret
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_launch_secret {
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__u64 hdr_uaddr; /* userspace address containing the packet header */
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__u32 hdr_len;
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__u64 guest_uaddr; /* the guest memory region where the secret should be injected */
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__u32 guest_len;
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__u64 trans_uaddr; /* the hypervisor memory region which contains the secret */
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__u32 trans_len;
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};
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10. KVM_SEV_GET_ATTESTATION_REPORT
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----------------------------------
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The KVM_SEV_GET_ATTESTATION_REPORT command can be used by the hypervisor to query the attestation
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report containing the SHA-256 digest of the guest memory and VMSA passed through the KVM_SEV_LAUNCH
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commands and signed with the PEK. The digest returned by the command should match the digest
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used by the guest owner with the KVM_SEV_LAUNCH_MEASURE.
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If len is zero on entry, the measurement blob length is written to len and
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uaddr is unused.
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Parameters (in): struct kvm_sev_attestation
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Returns: 0 on success, -negative on error
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struct kvm_sev_attestation_report {
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__u8 mnonce[16]; /* A random mnonce that will be placed in the report */
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__u64 uaddr; /* userspace address where the report should be copied */
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__u32 len;
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};
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11. KVM_SEV_SEND_START
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----------------------
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The KVM_SEV_SEND_START command can be used by the hypervisor to create an
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outgoing guest encryption context.
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If session_len is zero on entry, the length of the guest session information is
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written to session_len and all other fields are not used.
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Parameters (in): struct kvm_sev_send_start
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_send_start {
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__u32 policy; /* guest policy */
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__u64 pdh_cert_uaddr; /* platform Diffie-Hellman certificate */
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__u32 pdh_cert_len;
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__u64 plat_certs_uaddr; /* platform certificate chain */
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__u32 plat_certs_len;
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__u64 amd_certs_uaddr; /* AMD certificate */
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__u32 amd_certs_len;
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__u64 session_uaddr; /* Guest session information */
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__u32 session_len;
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};
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12. KVM_SEV_SEND_UPDATE_DATA
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----------------------------
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The KVM_SEV_SEND_UPDATE_DATA command can be used by the hypervisor to encrypt the
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outgoing guest memory region with the encryption context creating using
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KVM_SEV_SEND_START.
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If hdr_len or trans_len are zero on entry, the length of the packet header and
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transport region are written to hdr_len and trans_len respectively, and all
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other fields are not used.
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Parameters (in): struct kvm_sev_send_update_data
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_launch_send_update_data {
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__u64 hdr_uaddr; /* userspace address containing the packet header */
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__u32 hdr_len;
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__u64 guest_uaddr; /* the source memory region to be encrypted */
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__u32 guest_len;
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__u64 trans_uaddr; /* the destination memory region */
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__u32 trans_len;
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};
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13. KVM_SEV_SEND_FINISH
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------------------------
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After completion of the migration flow, the KVM_SEV_SEND_FINISH command can be
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issued by the hypervisor to delete the encryption context.
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Returns: 0 on success, -negative on error
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14. KVM_SEV_SEND_CANCEL
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------------------------
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After completion of SEND_START, but before SEND_FINISH, the source VMM can issue the
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SEND_CANCEL command to stop a migration. This is necessary so that a cancelled
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migration can restart with a new target later.
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Returns: 0 on success, -negative on error
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15. KVM_SEV_RECEIVE_START
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-------------------------
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The KVM_SEV_RECEIVE_START command is used for creating the memory encryption
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context for an incoming SEV guest. To create the encryption context, the user must
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provide a guest policy, the platform public Diffie-Hellman (PDH) key and session
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information.
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Parameters: struct kvm_sev_receive_start (in/out)
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_receive_start {
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__u32 handle; /* if zero then firmware creates a new handle */
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__u32 policy; /* guest's policy */
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__u64 pdh_uaddr; /* userspace address pointing to the PDH key */
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__u32 pdh_len;
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__u64 session_uaddr; /* userspace address which points to the guest session information */
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__u32 session_len;
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};
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On success, the 'handle' field contains a new handle and on error, a negative value.
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For more details, see SEV spec Section 6.12.
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16. KVM_SEV_RECEIVE_UPDATE_DATA
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-------------------------------
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The KVM_SEV_RECEIVE_UPDATE_DATA command can be used by the hypervisor to copy
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the incoming buffers into the guest memory region with encryption context
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created during the KVM_SEV_RECEIVE_START.
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Parameters (in): struct kvm_sev_receive_update_data
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Returns: 0 on success, -negative on error
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::
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struct kvm_sev_launch_receive_update_data {
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__u64 hdr_uaddr; /* userspace address containing the packet header */
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__u32 hdr_len;
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__u64 guest_uaddr; /* the destination guest memory region */
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__u32 guest_len;
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__u64 trans_uaddr; /* the incoming buffer memory region */
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__u32 trans_len;
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};
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17. KVM_SEV_RECEIVE_FINISH
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--------------------------
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After completion of the migration flow, the KVM_SEV_RECEIVE_FINISH command can be
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issued by the hypervisor to make the guest ready for execution.
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Returns: 0 on success, -negative on error
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References
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==========
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See [white-paper]_, [api-spec]_, [amd-apm]_ and [kvm-forum]_ for more info.
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.. [white-paper] http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf
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.. [api-spec] https://support.amd.com/TechDocs/55766_SEV-KM_API_Specification.pdf
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.. [amd-apm] https://support.amd.com/TechDocs/24593.pdf (section 15.34)
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.. [kvm-forum] https://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf
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