virt-qemu-sev-validate - Man Page

validate a domain AMD SEV launch measurement

Synopsis

virt-qemu-sev-validate [Options]

Description

This program validates the reported measurement for a domain launched with AMD SEV. If the program exits with a status of zero, the guest owner can be confident that their guest OS is running under the protection offered by the SEV / SEV-ES platform.

Note that the level of protection varies depending on the AMD SEV platform generation and describing the differences is outside the scope of this document.

For the results of this program to be considered trustworthy, it is required to be run on a machine that is already trusted by the guest owner. This could be a machine that the guest owner has direct physical control over, or it could be another virtual machine protected by AMD SEV that has already had its launch measurement validated. Running this program on the virtualization host will not produce an answer that can be trusted.

If told to connect to libvirt, it will refuse to use a libvirt connection that is local to the machine, since that cannot be trusted. For the sake of testing or demonstration purposes, however, it can be forced to run in this scenario using the --insecure flag. The result will, of course, still not be trustworthy.

Options

Common options

-h, --help

Display command line help usage then exit.

-d, --debug

Show debug information while running

-q, --quiet

Don't print information about the attestation result.

Guest state options

These options provide information about the state of the guest that needs its boot attested.

--measurement BASE64-STRING

The launch measurement reported by the hypervisor of the domain to be validated. The measurement must be 48 bytes of binary data encoded as a base64 string.

--api-major VERSION

The SEV API major version of the hypervisor the domain is running on.

--api-minor VERSION

The SEV API major version of the hypervisor the domain is running on.

--build-id ID

The SEV build ID of the hypervisor the domain is running on.

--policy POLiCY

The policy bitmask associated with the session launch data of the domain to be validated.

Guest config options

These options provide items needed to calculate the expected domain launch measurement. This will then be compared to the reported launch measurement.

-f PATH, --firmware=PATH

Path to the firmware loader binary. This is the EDK2 build that knows how to initialize AMD SEV. For the validation to be trustworthy it important that the firmware build used has no support for loading non-volatile variables from NVRAM, even if NVRAM is expose to the guest.

-k PATH, --kernel=PATH

Path to the kernel binary if doing direct kernel boot.

-r PATH, --initrd=PATH

Path to the initrd binary if doing direct kernel boot. Defaults to zero length content if omitted.

-e STRING, --cmdline=STRING

String containing any kernel command line parameters used during boot of the domain. Defaults to the empty string if omitted.

-n COUNT, --num-cpus=COUNT

The number of virtual CPUs for the domain. This is required when the domain policy is set to require SEV-ES.

-0 PATH, --vmsa-cpu0=PATH

Path to the VMSA initial state for the boot CPU. This is required when the domain policy is set to require SEV-ES. The file contents must be exactly 4096 bytes in length.

-1 PATH, --vmsa-cpu1=PATH

Path to the VMSA initial state for the non-boot CPU. This is required when the domain policy is set to require SEV-ES and the domain has more than one CPU present. The file contents must be exactly 4096 bytes in length.

--tik PATH

TIK file for domain. This file must be exactly 16 bytes in size and contains the unique transport integrity key associated with the domain session launch data. This is mutually exclusive with the --tk argument.

--tek PATH

TEK file for domain. This file must be exactly 16 bytes in size and contains the unique transport encryption key associated with the domain session launch data. This is mutually exclusive with the --tk argument.

--tk PATH

TEK/TIK combined file for the domain. This file must be exactly 32 bytes in size, with the first 16 bytes containing the TEK and the last 16 bytes containing the TIK.  This is mutually exclusive with the --tik and --tek arguments.

Libvirt options

These options are used when connecting to libvirt to automatically obtain state and configuration information about the domain to be attested.

-c, --connect URI

Libvirt connection URI. For the validation to be trustworthy this must be a URI resolving to a remote virtualization host. This requirement can be overridden using the --insecure argument.

-o, --domain ID|NAME|UUID

Domain ID, or domain name or domain UUID. Used to identify which libvirt domain is to have its launch measured. The domain must be running, and would usually have been started in a paused state, to allow validation to be performed before guest CPUs begin execution.

-i, --insecure

Proceed even if usage scenario is known to be insecure. This allows the program to connect to a local libvirt hypervisor and rely on file content from the virtualization host. It also allows the validation to proceed even if the virtual machine CPUs are not in the initial paused state. The result of the validation must not be trusted.

-g, --ignore-config

Do not attempt to sanity check the domain config. The default behaviour is to print out errors if identifying configuration elements in the guest XML that would invalidate the launch measurement. This can help the guest owner to understand any configuration mistakes that have been made. If the --ignore-config argument is given, this sanity checking of configuration will be skipped. The result is that the validation will likely be reported as failed.

Secret injection options

These options provide a way to inject a secret if validation of the launch measurement passes.

--inject-secret ALIAS-OR-GUID:PATH

Path to a file containing a secret to inject into the guest OS. Typical usage would be to supply a password for unlocking the root filesystem full disk encryption. ALIAS can be one of the well known secrets:

  • luks-key - bytes to use as a key for unlocking a LUKS key slot. GUID of 736869e5-84f0-4973-92ec-06879ce3da0b.

Alternatively GUID refers to an arbitrary UUID of the callers choosing. The contents of PATH are defined by the requirements of the associated GUID, and will used as-is without modification. In particular be aware:

  • Avoid unwanted trailing newline characters in PATH unless mandated by the GUID.
  • Any trailing NUL byte must be explicitly included in PATH if mandated by the GUID.

This argument can be repeated multiple times, provided a different GUID is given for each instance.

--secret-header PATH

Path to a file in which the injected secret header will be written in base64 format and later injected into the domain. This is required if there is no connection to libvirt, otherwise the secret will be directly injected.

--secret-payload PATH

Path to a file in which the injected secret payload will be written in base64 format and later injected into the domain. This is required if there is no connection to libvirt, otherwise the secret will be directly injected.

Examples

Fully offline execution

This scenario allows a measurement to be securely validated in a completely offline state without any connection to the hypervisor host. All required data items must be provided as command line parameters. This usage model is considered secure, because all input data is provided by the user.

Validate the measurement of a SEV guest booting from disk:

# virt-qemu-sev-validate \
    --firmware OVMF.sev.fd \
    --tk this-guest-tk.bin \
    --measurement Zs2pf19ubFSafpZ2WKkwquXvACx9Wt/BV+eJwQ/taO8jhyIj/F8swFrybR1fZ2ID \
    --api-major 0 \
    --api-minor 24 \
    --build-id 13 \
    --policy 3

Validate the measurement of a SEV guest with direct kernel boot:

# virt-dom-sev-validate \
    --firmware OVMF.sev.fd \
    --kernel vmlinuz-5.11.12 \
    --initrd initramfs-5.11.12 \
    --cmdline "root=/dev/vda1" \
    --tk this-guest-tk.bin \
    --measurement Zs2pf19ubFSafpZ2WKkwquXvACx9Wt/BV+eJwQ/taO8jhyIj/F8swFrybR1fZ2ID \
    --api-major 0 \
    --api-minor 24 \
    --build-id 13 \
    --policy 3

Validate the measurement of a SEV-ES SMP guest booting from disk:

# virt-dom-sev-validate \
    --firmware OVMF.sev.fd \
    --num-cpus 2 \
    --vmsa-cpu0 vmsa0.bin \
    --vmsa-cpu1 vmsa1.bin \
    --tk this-guest-tk.bin \
    --measurement Zs2pf19ubFSafpZ2WKkwquXvACx9Wt/BV+eJwQ/taO8jhyIj/F8swFrybR1fZ2ID \
    --api-major 0 \
    --api-minor 24 \
    --build-id 13 \
    --policy 7

Validate the measurement of a SEV-ES SMP guest booting from disk, with automatically constructed VMSA:

# virt-dom-sev-validate \
    --firmware OVMF.sev.fd \
    --num-cpus 2 \
    --cpu-family 23 \
    --cpu-model 49 \
    --cpu-stepping 0 \
    --tk this-guest-tk.bin \
    --measurement Zs2pf19ubFSafpZ2WKkwquXvACx9Wt/BV+eJwQ/taO8jhyIj/F8swFrybR1fZ2ID \
    --api-major 0 \
    --api-minor 24 \
    --build-id 13 \
    --policy 7

Validate the measurement of a SEV guest booting from disk and inject a disk password on success:

# virt-dom-sev-validate \
    --loader OVMF.sev.fd \
    --tk this-guest-tk.bin \
    --measurement Zs2pf19ubFSafpZ2WKkwquXvACx9Wt/BV+eJwQ/taO8jhyIj/F8swFrybR1fZ2ID \
    --api-major 0 \
    --api-minor 24 \
    --build-id 13 \
    --policy 3 \
    --disk-password passwd.txt \
    --secret-header secret-header.b64 \
    --secret-payload secret-payload.b64

The secret-header.b64 and secret-payload.b64 files can now be sent to the virtualization host for injection.

Fetch from remote libvirt

This scenario allows fetching certain data from a remote hypervisor via a connection to libvirt. It will aid in debugging by analysing the guest configuration and reporting anything that could invalidate the measurement of the guest. This usage model is considered secure, because the limited information obtained from the untrusted hypervisor cannot be used to change the result.

Validate the measurement of a SEV guest booting from disk:

# virt-qemu-sev-validate \
    --connect qemu+ssh://root@some.remote.host/system \
    --firmware OVMF.sev.fd \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV guest with direct kernel boot:

# virt-dom-sev-validate \
    --connect qemu+ssh://root@some.remote.host/system \
    --firmware OVMF.sev.fd \
    --kernel vmlinuz-5.11.12 \
    --initrd initramfs-5.11.12 \
    --cmdline "root=/dev/vda1" \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV-ES SMP guest booting from disk:

# virt-dom-sev-validate \
    --connect qemu+ssh://root@some.remote.host/system \
    --firmware OVMF.sev.fd \
    --num-cpus 2 \
    --vmsa-cpu0 vmsa0.bin \
    --vmsa-cpu1 vmsa1.bin \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV-ES SMP guest booting from disk, with automatically constructed VMSA:

# virt-dom-sev-validate \
    --connect qemu+ssh://root@some.remote.host/system \
    --firmware OVMF.sev.fd \
    --cpu-family 23 \
    --cpu-model 49 \
    --cpu-stepping 0 \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV guest booting from disk and inject a disk password on success:

# virt-dom-sev-validate \
    --connect qemu+ssh://root@some.remote.host/system \
    --loader OVMF.sev.fd \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64 \
    --disk-password passwd.txt

Fetch from local libvirt

This scenario allows fetching all data from the local hypervisor via a connection to libvirt. It is only to be used for the purpose of testing, debugging, or demonstrations, because running on the local hypervisor is not a secure scenario. To enable this usage, the --insecure flag must be specified. Given a pointer to the libvirt guest to validate, all information needed to perform a validation, except the TIK/TEK pair can be acquired automatically.

Validate the measurement of a SEV guest booting from disk:

# virt-qemu-sev-validate \
    --insecure \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV guest with direct kernel boot:

# virt-dom-sev-validate \
    --insecure \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV-ES SMP guest booting from disk:

# virt-dom-sev-validate \
    --insecure \
    --vmsa-cpu0 vmsa0.bin \
    --vmsa-cpu1 vmsa1.bin \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV-ES SMP guest booting from disk, with automatically constructed VMSA:

# virt-dom-sev-validate \
    --insecure \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64

Validate the measurement of a SEV guest booting from disk and inject a disk password on success:

# virt-dom-sev-validate \
    --insecure \
    --tk this-guest-tk.bin \
    --domain fedora34x86_64 \
    --disk-password passwd.txt

Common Mistakes Checklist

The complexity of configuring a guest and validating its boot measurement means it is very likely to see the failure:

ERROR: Measurement does not match, VM is not trustworthy

This error message assumes the worst, but in most cases will failure will be a result of either mis-configuring the guest, or passing the wrong information when trying to validate it. The following information is a guide for what items to check in order to stand the best chance of diagnosing the problem

Best practice is to run this tool in completely offline mode and pass all information as explicit command line parameters. When debugging failures, however, it can be useful to tell it to connect to libvirt and fetch information. If connecting to a remote libvirt instance, it will fetch any information that can be trusted, which is the basic VM launch state data. It will also sanity check the XML configuration to identify some common mistakes. If the --insecure flag is passed it can extract some configuration information and use that for the attestation process.

If the mistake still can't be identified, then this tool can be run on the virtualization host. In that scenario the only three command line parameters required are for the TIK, TEK and libvirt domain name. It should be able to automatically determine all the other information required. If it still reports a failure, this points very strongly to the TIK/TEK pair not matching the configured DH certificate and session blob.

The --debug flag will display hashes and/or hex dumps for various pieces of information used in the attestation process. Comparing the --debug output from running on the hypervisor host, against that obtained when running in offline mode can give further guidance to which parameter is inconsistent.

As mentioned earlier in this document, bear in mind that in general any attestation answers obtained from running on the hypervisor host should not be trusted. So if a configuration mistake is identified it is strongly recommended to re-run the attestation in offline mode on a trusted machine.

Exit Status

Upon successful attestation of the launch measurement, an exit status of 0 will be set.

Upon failure to attest the launch measurement one of the following codes will be set:

Author

Daniel P. Berrangé

Bugs

Please report all bugs you discover.  This should be done via either:

  1. the mailing list

    https://libvirt.org/contact.html

  2. the bug tracker

    https://libvirt.org/bugs.html

Alternatively, you may report bugs to your software distributor / vendor.

License

virt-qemu-sev-validate is distributed under the terms of the GNU LGPL v2.1+. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE

See Also

virsh(1), SEV launch security usage, https://www.libvirt.org/

Info

Virtualization Support