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Chapter 15. Securing virtual machines

As an administrator of a RHEL 8 system with virtual machines (VMs), ensuring that your VMs are as secure as possible significantly lowers the risk of your guest and host OSs being infected by malicious software.

This document outlines the mechanics of securing VMs on a RHEL 8 host and provides a list of methods to increase the security of your VMs.

15.1. How security works in virtual machines

When using virtual machines (VMs), multiple operating systems can be housed within a single host machine. These systems are connected with the host through the hypervisor, and usually also through a virtual network. As a consequence, each VM can be used as a vector for attacking the host with malicious software, and the host can be used as a vector for attacking any of the VMs.

Figure 15.1. A potential malware attack vector on a virtualization host

virt sec successful attack

Because the hypervisor uses the host kernel to manage VMs, services running on the VM’s operating system are frequently used for injecting malicious code into the host system. However, you can protect your system against such security threats by using a number of security features on your host and your guest systems.

These features, such as SELinux or QEMU sandboxing, provide various measures that make it more difficult for malicious code to attack the hypervisor and transfer between your host and your VMs.

Figure 15.2. Prevented malware attacks on a virtualization host

virt sec prevented attack

Many of the features that RHEL 8 provides for VM security are always active and do not have to be enabled or configured. For details, see Automatic features for virtual machine security.

In addition, you can adhere to a variety of best practices to minimize the vulnerability of your VMs and your hypervisor. For more information, see Best practices for securing virtual machines.

15.2. Best practices for securing virtual machines

Following the instructions below significantly decreases the risk of your virtual machines being infected with malicious code and used as attack vectors to infect your host system.

On the guest side:

  • Secure the virtual machine as if it was a physical machine. The specific methods available to enhance security depend on the guest OS.

    If your VM is running RHEL 8, see Securing Red Hat Enterprise Linux 8 for detailed instructions on improving the security of your guest system.

On the host side:

  • When managing VMs remotely, use cryptographic utilities such as SSH and network protocols such as SSL for connecting to the VMs.
  • Ensure SELinux is in Enforcing mode:

    # getenforce

    If SELinux is disabled or in Permissive mode, see the Using SELinux document for instructions on activating Enforcing mode.


    SELinux Enforcing mode also enables the sVirt RHEL 8 feature. This is a set of specialized SELinux booleans for virtualization, which can be manually adjusted for fine-grained VM security management.

  • Use VMs with SecureBoot:

    SecureBoot is a feature that ensures that your VM is running a cryptographically signed OS. This prevents VMs whose OS has been altered by a malware attack from booting.

    SecureBoot can only be applied when installing a Linux VM that uses OVMF firmware. For instructions, see Creating a SecureBoot virtual machine.

  • Do not use qemu-* commands, such as qemu-kvm.

    QEMU is an essential component of the virtualization architecture in RHEL 8, but it is difficult to manage manually, and improper QEMU configurations may cause security vulnerabilities. Therefore, using most qemu-* commands is not supported by Red Hat. Instead, use libvirt utilities, such as virsh, virt-install, and virt-xml, as these orchestrate QEMU according to the best practices.

    Note, however, that the qemu-img utility is supported for management of virtual disk images.

15.3. Creating a SecureBoot virtual machine

You can create a Linux virtual machine (VM) that uses the SecureBoot feature, which ensures that your VM is running a cryptographically signed OS. This can be useful if the guest OS of a VM has been altered by malware. In such a scenario, SecureBoot prevents the VM from booting, which stops the potential spread of the malware to your host machine.


  • The VM is the Q35 machine type.
  • The edk2-OVMF packages is installed:

    # yum install edk2-ovmf
  • An operating system (OS) installation source is available locally or on a network. This can be one of the following formats:

    • An ISO image of an installation medium
    • A disk image of an existing VM installation


      Installing from a host CD-ROM or DVD-ROM device is not possible in RHEL 8. If you select a CD-ROM or DVD-ROM as the installation source when using any VM installation method available in RHEL 8, the installation will fail. For more information, see the Red Hat Knowledgebase.

  • Optional: A Kickstart file can be provided for faster and easier configuration of the installation.


  1. Use the virt-install command to create a VM as detailed in Creating virtual machines by using the command-line interface. For the --boot option, use the uefi,nvram_template=/usr/share/OVMF/OVMF_VARS.secboot.fd value. This uses the OVMF_VARS.secboot.fd and OVMF_CODE.secboot.fd files as templates for the VM’s non-volatile RAM (NVRAM) settings, which enables the SecureBoot feature.

    For example:

    # virt-install --name rhel8sb --memory 4096 --vcpus 4 --os-variant rhel8.0 --boot uefi,nvram_template=/usr/share/OVMF/OVMF_VARS.secboot.fd --disk boot_order=2,size=10 --disk boot_order=1,device=cdrom,bus=scsi,path=/images/RHEL-8.0-installation.iso
  2. Follow the OS installation procedure according to the instructions on the screen.


  1. After the guest OS is installed, access the VM’s command line by opening the terminal in the graphical guest console or connecting to the guest OS using SSH.
  2. To confirm that SecureBoot has been enabled on the VM, use the mokutil --sb-state command:

    # mokutil --sb-state
    SecureBoot enabled

15.4. Limiting what actions are available to virtual machine users

In some cases, actions that users of virtual machines (VMs) hosted on RHEL 8 can perform by default may pose a security risk. If that is the case, you can limit the actions available to VM users by configuring the libvirt daemons to use the polkit policy toolkit on the host machine.


  1. Optional: Ensure your system’s polkit control policies related to libvirt are set up according to your preferences.

    1. Find all libvirt-related files in the /usr/share/polkit-1/actions/ and /usr/share/polkit-1/rules.d/ directories.

      # ls /usr/share/polkit-1/actions | grep libvirt
      # ls /usr/share/polkit-1/rules.d | grep libvirt
    2. Open the files and review the rule settings.

      For information about reading the syntax of polkit control policies, use man polkit.

    3. Modify the libvirt control policies. To do so:

      1. Create a new .rules file in the /etc/polkit-1/rules.d/ directory.
      2. Add your custom policies to this file, and save it.

        For further information and examples of libvirt control policies, see the libvirt upstream documentation.

  2. Configure your VMs to use access policies determined by polkit.

    To do so, uncomment the access_drivers = [ "polkit" ] line in the /etc/libvirt/libvirtd.conf file.

    # sed -i 's/#access_drivers = \[ "polkit" \]/access_drivers = \[ "polkit" \]/' /etc/libvirt/libvirtd.conf
  3. Restart the libvirtd service.

    # systemctl restart libvirtd


  • As a user whose VM actions you intended to limit, perform one of the restricted actions.

    For example, if unprivileged users are restricted from viewing VMs created in the system session:

    $ virsh -c qemu:///system list --all
    Id   Name           State

    If this command does not list any VMs even though one or more VMs exist on your system, polkit successfully restricts the action for unprivileged users.


Additional resources

15.5. Automatic features for virtual machine security

In addition to manual means of improving the security of your virtual machines listed in Best practices for securing virtual machines, a number of security features are provided by the libvirt software suite and are automatically enabled when using virtualization in RHEL 8. These include:

System and session connections

To access all the available utilities for virtual machine management in RHEL 8, you need to use the system connection of libvirt (qemu:///system). To do so, you must have root privileges on the system or be a part of the libvirt user group.

Non-root users that are not in the libvirt group can only access a session connection of libvirt (qemu:///session), which has to respect the access rights of the local user when accessing resources. For example, using the session connection, you cannot detect or access VMs created in the system connection or by other users. Also, available VM networking configuration options are significantly limited.


The RHEL 8 documentation assumes you have system connection privileges.

Virtual machine separation
Individual VMs run as isolated processes on the host, and rely on security enforced by the host kernel. Therefore, a VM cannot read or access the memory or storage of other VMs on the same host.
QEMU sandboxing
A feature that prevents QEMU code from executing system calls that can compromise the security of the host.
Kernel Address Space Randomization (KASLR)
Enables randomizing the physical and virtual addresses at which the kernel image is decompressed. Thus, KASLR prevents guest security exploits based on the location of kernel objects.

15.6. SELinux booleans for virtualization

For fine-grained configuration of virtual machines security on a RHEL 8 system, you can configure SELinux booleans on the host to ensure the hypervisor acts in a specific way.

To list all virtualization-related booleans and their statuses, use the getsebool -a | grep virt command:

$ getsebool -a | grep virt
virt_sandbox_use_netlink --> off
virt_sandbox_use_sys_admin --> off
virt_transition_userdomain --> off
virt_use_comm --> off
virt_use_execmem --> off
virt_use_fusefs --> off

To enable a specific boolean, use the setsebool -P boolean_name on command as root. To disable a boolean, use setsebool -P boolean_name off.

The following table lists virtualization-related booleans available in RHEL 8 and what they do when enabled:

Table 15.1. SELinux virtualization booleans

SELinux BooleanDescription


Enables non-root users to create and transition VMs to sVirt.


Enables unprivileged users to create and transition VMs to sVirt.


Enables sandbox containers to send audit messages.


Enables sandbox containers to use netlink system calls.


Enables sandbox containers to use sys_admin system calls, such as mount.


Enables virtual processes to run as user domains.


Enables virt to use serial/parallel communication ports.


Enables confined virtual guests to use executable memory and executable stack.


Enables virt to read FUSE mounted files.


Enables virt to manage NFS mounted files.


Enables virt to interact with rawip sockets.


Enables virt to manage CIFS mounted files.


Enables confined virtual guests to interact with the sanlock.


Enables virt to use USB devices.


Enables virtual machine to interact with the X Window System.

15.7. Setting up IBM Secure Execution on IBM Z

When using IBM Z hardware to run a RHEL 8 host, you can improve the security of your virtual machines (VMs) by configuring IBM Secure Execution for the VMs.

IBM Secure Execution, also known as Protected Virtualization, prevents the host system from accessing a VM’s state and memory contents. As a result, even if the host is compromised, it cannot be used as a vector for attacking the guest operating system. In addition, Secure Execution can be used to prevent untrusted hosts from obtaining sensitive information from the VM.

The following procedure describes how to convert an existing VM on an IBM Z host into a secured VM.


  • The system hardware is one of the following:

    • IBM z15 or later
    • IBM LinuxONE III or later
  • The Secure Execution feature is enabled for your system. To verify, use:

    # grep facilities /proc/cpuinfo | grep 158

    If this command displays any output, your CPU is compatible with Secure Execution.

  • The kernel includes support for Secure Execution. To confirm, use:

    # ls /sys/firmware | grep uv

    If the command generates any output, your kernel supports Secure Execution.

  • The host CPU model contains the unpack facility. To confirm, use:

    # virsh domcapabilities | grep unpack
    <feature policy='require' name='unpack'/>

    If the command generates the above output, your CPU host model is compatible with Secure Execution.

  • The CPU mode of the VM is set to host-model. To confirm this, use the following and replace vm-name with the name of your VM.

    # virsh dumpxml vm-name | grep "<cpu mode='host-model'/>"

    If the command generates any output, the VM’s CPU mode is set correctly.

  • You have obtained and verified the IBM Z host key document. For instructions to do so, see Verifying the host key document in IBM documentation.


Do the following steps on your host:

  1. Add the prot_virt=1 kernel parameter to the boot configuration of the host.

    # grubby --update-kernel=ALL --args="prot_virt=1"
  2. Update the boot menu:

    # zipl

  3. Use virsh edit to modify the XML configuration of the VM you want to secure.
  4. Add <launchSecurity type="s390-pv"/> to the under the </devices> line. For example:

      <launchSecurity type="s390-pv"/>
  5. If the <devices> section of the configuration includes a virtio-rng device (<rng model="virtio">), remove all lines of the <rng> </rng> block.

Do the following steps in the guest operating system of the VM you want to secure.

  1. Create a parameter file. For example:

    # touch ~/secure-parameters
  2. In the /boot/loader/entries directory, identify the boot loader entry with the latest version:

    # ls /boot/loader/entries -l
    -rw-r--r--. 1 root root  281 Oct  9 15:51 3ab27a195c2849429927b00679db15c1-4.18.0-240.el8.s390x.conf
  3. Retrieve the kernel options line of the boot loader entry:

    # cat /boot/loader/entries/3ab27a195c2849429927b00679db15c1-4.18.0-240.el8.s390x.conf | grep options
    options root=/dev/mapper/rhel-root
  4. Add the content of the options line and swiotlb=262144 to the created parameters file.

    # echo "root=/dev/mapper/rhel-root crashkernel=auto swiotlb=262144" > ~/secure-parameters
  5. Generate an IBM Secure Execution image.

    For example, the following creates a /boot/secure-image secured image based on the /boot/vmlinuz-4.18.0-240.el8.s390x image, using the secure-parameters file, the /boot/initramfs-4.18.0-240.el8.s390x.img initial RAM disk file, and the HKD-8651-000201C048.crt host key document.

    # genprotimg -i /boot/vmlinuz-4.18.0-240.el8.s390x -r /boot/initramfs-4.18.0-240.el8.s390x.img -p ~/secure-parameters -k HKD-8651-00020089A8.crt -o /boot/secure-image

    By using the genprotimg utility creates the secure image, which contains the kernel parameters, initial RAM disk, and boot image.

  6. Update the VM’s boot menu to boot from the secure image. In addition, remove the lines starting with initrd and options, as they are not needed.

    For example, in a RHEL 8.3 VM, the boot menu can be edited in the /boot/loader/entries/ directory:

    # cat /boot/loader/entries/3ab27a195c2849429927b00679db15c1-4.18.0-240.el8.s390x.conf
    title Red Hat Enterprise Linux 8.3
    version 4.18.0-240.el8.s390x
    linux /boot/secure-image
  7. Create the bootable disk image:

    # zipl -V
  8. Securely remove the original unprotected files. For example:

    # shred /boot/vmlinuz-4.18.0-240.el8.s390x
    # shred /boot/initramfs-4.18.0-240.el8.s390x.img
    # shred secure-parameters

    The original boot image, the initial RAM image, and the kernel parameter file are unprotected, and if they are not removed, VMs with Secure Execution enabled can still be vulnerable to hacking attempts or sensitive data mining.


  • On the host, use the virsh dumpxml utility to confirm the XML configuration of the secured VM. The configuration must include the <launchSecurity type="s390-pv"/> element, and no <rng model="virtio"> lines.

    # virsh dumpxml vm-name
      <cpu mode='host-model'/>
        <disk type='file' device='disk'>
          <driver name='qemu' type='qcow2' cache='none' io='native'>
          <source file='/var/lib/libvirt/images/secure-guest.qcow2'/>
          <target dev='vda' bus='virtio'/>
        <interface type='network'>
          <source network='default'/>
          <model type='virtio'/>
        <console type='pty'/>
        <memballoon model='none'/>
      <launchSecurity type="s390-pv"/>

15.8. Attaching cryptographic coprocessors to virtual machines on IBM Z

To use hardware encryption in your virtual machine (VM) on an IBM Z host, create mediated devices from a cryptographic coprocessor device and assign them to the intended VMs. For detailed instructions, see below.


  • Your host is running on IBM Z hardware.
  • The cryptographic coprocessor is compatible with device assignment. To confirm this, ensure that the type of your coprocessor is listed as CEX4 or later.

    # lszcrypt -V
    05         CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4card
    05.0004    CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue
    05.00ab    CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue
  • The vfio_ap kernel module is loaded. To verify, use:

    # lsmod | grep vfio_ap
    vfio_ap         24576  0

    To load the module, use:

    # modprobe vfio_ap
  • The s390utils version supports ap handling:

    # lszdev --list-types
    ap           Cryptographic Adjunct Processor (AP) device


  1. Obtain the decimal values for the devices that you want to assign to the VM. For example, for the devices 05.0004 and 05.00ab:

    # echo "obase=10; ibase=16; 04" | bc
    # echo "obase=10; ibase=16; AB" | bc
  2. On the host, reassign the devices to the vfio-ap drivers:

    # chzdev -t ap apmask=-5 aqmask=-4,-171

    To assign the devices persistently, use the -p flag.

  3. Verify that the cryptographic devices have been reassigned correctly.

    # lszcrypt -V
    05          CEX5C CCA-Coproc  -              1        0     11     08 S--D--N--  cex4card
    05.0004     CEX5C CCA-Coproc  -              1        0     11     08 S--D--N--  vfio_ap
    05.00ab     CEX5C CCA-Coproc  -              1        0     11     08 S--D--N--  vfio_ap

    If the DRIVER values of the domain queues changed to vfio_ap, the reassignment succeeded.

  4. Create an XML snippet that defines a new mediated device.

    The following example shows defining a persistent mediated device and assigning queues to it. Specifically, the vfio_ap.xml XML snippet in this example assigns a domain adapter 0x05, domain queues 0x0004 and 0x00ab, and a control domain 0x00ab to the mediated device.

    # vim vfio_ap.xml
      <capability type="mdev">
        <type id="vfio_ap-passthrough"/>
        <attr name='assign_adapter' value='0x05'/>
        <attr name='assign_domain' value='0x0004'/>
        <attr name='assign_domain' value='0x00ab'/>
        <attr name='assign_control_domain' value='0x00ab'/>
  5. Create a new mediated device from the vfio_ap.xml XML snippet.

    # virsh nodedev-define vfio_ap.xml
    Node device 'mdev_8f9c4a73_1411_48d2_895d_34db9ac18f85_matrix' defined from 'vfio_ap.xml'
  6. Start the mediated device that you created in the previous step, in this case mdev_8f9c4a73_1411_48d2_895d_34db9ac18f85_matrix.

    # virsh nodedev-start mdev_8f9c4a73_1411_48d2_895d_34db9ac18f85_matrix
    Device mdev_8f9c4a73_1411_48d2_895d_34db9ac18f85_matrix started
  7. Check that the configuration has been applied correctly

    # cat /sys/devices/vfio_ap/matrix/mdev_supported_types/vfio_ap-passthrough/devices/669d9b23-fe1b-4ecb-be08-a2fabca99b71/matrix

    If the output contains the numerical values of queues that you have previously assigned to vfio-ap, the process was successful.

  8. Attach the mediated device to the VM.

    1. Display the UUID of the mediated device that you created and save it for the next step.

      # virsh nodedev-dumpxml mdev_8f9c4a73_1411_48d2_895d_34db9ac18f85_matrix
        <capability type='mdev'>
          <type id='vfio_ap-passthrough'/>
          <iommuGroup number='0'/>
          <attr name='assign_adapter' value='0x05'/>
          <attr name='assign_domain' value='0x0004'/>
          <attr name='assign_domain' value='0x00ab'/>
          <attr name='assign_control_domain' value='0x00ab'/>
    2. Create and open an XML file for the cryptographic card mediated device. For example:

      # vim crypto-dev.xml
    3. Add the following lines to the file and save it. Replace the uuid value with the UUID you obtained in step a.

      <hostdev mode='subsystem' type='mdev' managed='no' model='vfio-ap'>
          <address uuid='8f9c4a73-1411-48d2-895d-34db9ac18f85'/>
    4. Use the XML file to attach the mediated device to the VM. For example, to permanently attach a device defined in the crypto-dev.xml file to the running testguest1 VM:

      # virsh attach-device testguest1 crypto-dev.xml --live --config

      The --live option attaches the device to a running VM only, without persistence between boots. The --config option makes the configuration changes persistent. You can use the --config option alone to attach the device to a shut-down VM.

      Note that each UUID can only be assigned to one VM at a time.


  1. Ensure that the guest operating system detects the assigned cryptographic devices.

    # lszcrypt -V
    05          CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4card
    05.0004     CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue
    05.00ab     CEX5C CCA-Coproc  online         1        0     11     08 S--D--N--  cex4queue

    The output of this command in the guest operating system will be identical to that on a host logical partition with the same cryptographic coprocessor devices available.

  2. In the guest operating system, confirm that a control domain has been successfully assigned to the cryptographic devices.

    # lszcrypt -d C
    DOMAIN 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
        00  .  .  .  .  U  .  .  .  .  .  .  .  .  .  .  .
        10  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        20  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        30  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        40  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        50  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        60  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        70  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        80  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        90  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        a0  .  .  .  .  .  .  .  .  .  .  .  B  .  .  .  .
        b0  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        c0  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        d0  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        e0  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
        f0  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
    C: Control domain
    U: Usage domain
    B: Both (Control + Usage domain)

    If lszcrypt -d C displays U and B intersections in the cryptographic device matrix, the control domain assignment was successful.

15.9. Enabling standard hardware security on Windows virtual machines

To secure Windows virtual machines (VMs), you can enable basic level security by using the standard hardware capabilities of the Windows device.


  • Make sure you have installed the latest WHQL certified VirtIO drivers.
  • Make sure the VM’s firmware supports UEFI boot.
  • Install the edk2-OVMF package on your host machine.

    # {PackageManagerCommand} install edk2-ovmf
  • Install the vTPM packages on your host machine.

    # {PackageManagerCommand} install swtpm libtpms
  • Make sure the VM is using the Q35 machine architecture.
  • Make sure you have the Windows installation media.


  1. Enable TPM 2.0 by adding the following parameters to the <devices> section in the VM’s XML configuration.

      <tpm model='tpm-crb'>
        <backend type='emulator' version='2.0'/>
  2. Install Windows in UEFI mode. For more information about how to do so, see Creating a SecureBoot virtual machine.
  3. Install the VirtIO drivers on the Windows VM. For more information about how to do so, see Installing virtio drivers on a Windows guest.
  4. In UEFI, enable Secure Boot. For more information about how to do so, see Secure Boot.


  • Ensure that the Device Security page on your Windows machine displays the following message:

    Settings > Update & Security > Windows Security > Device Security

    Your device meets the requirements for standard hardware security.

15.10. Enabling enhanced hardware security on Windows virtual machines

To further secure Windows virtual machines (VMs), you can enable virtualization-based protection of code integrity, also known as Hypervisor-Protected Code Integrity (HVCI).



  1. Open the XML configuration of the Windows VM. The following example opens the configuration of the Example-L1 VM:

    # virsh edit Example-L1
  2. Under the <cpu> section, specify the CPU mode and add the policy flag.

    • For Intel CPUs, enable the vmx policy flag.
    • For AMD CPUs, enable the svm policy flag.
    • If you do not wish to specify a custom CPU, you can set the <cpu mode> as host-passthrough.
    <cpu mode='custom' match='exact' check='partial'>
        <model fallback='allow'>Skylake-Client-IBRS</model>
        <topology sockets='1' dies='1' cores='4' threads='1'/>
        <feature policy='require' name='vmx'/>
  3. Save the XML configuration and reboot the VM.
  4. On the VMs operating system, navigate to the Core isolation details page:

    Settings > Update & Security > Windows Security > Device Security > Core isolation details

  5. Toggle the switch to enable Memory Integrity.
  6. Reboot the VM.

For other methods of enabling HVCI, see the relevant Microsoft documentation.


  • Ensure that the Device Security page on your Windows VM displays the following message:

    Settings > Update & Security > Windows Security > Device Security

    Your device meets the requirements for enhanced hardware security.
  • Alternatively, check System Information about the Windows VM:

    1. Run msinfo32.exe in a command prompt.
    2. Check if Credential Guard, Hypervisor enforced Code Integrity is listed under Virtualization-based security Services Running.