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