Virtual machine (VM) workloads run as unprivileged pods. So that VMs can use OpenShift Virtualization features, some pods are granted custom security policies that are not available to other pod owners:

  • An extended container_t SELinux policy applies to virt-launcher pods.

  • Security context constraints (SCCs) are defined for the kubevirt-controller service account.

About workload security

By default, virtual machine (VM) workloads do not run with root privileges in OpenShift Virtualization.

For each VM, a virt-launcher pod runs an instance of libvirt in session mode to manage the VM process. In session mode, the libvirt daemon runs as a non-root user account and only permits connections from clients that are running under the same user identifier (UID). Therefore, VMs run as unprivileged pods, adhering to the security principle of least privilege.

There are no supported OpenShift Virtualization features that require root privileges. If a feature requires root, it might not be supported for use with OpenShift Virtualization.

Extended SELinux policies for virt-launcher pods

The container_t SELinux policy for virt-launcher pods is extended to enable essential functions of OpenShift Virtualization.

  • The following policy is required for network multi-queue, which enables network performance to scale as the number of available vCPUs increases:

    • allow process self (tun_socket (relabelfrom relabelto attach_queue))

  • The following policy allows virt-launcher to read files under the /proc directory, including /proc/cpuinfo and /proc/uptime:

    • allow process proc_type (file (getattr open read))

  • The following policy allows libvirtd to relay network-related debug messages.

    • allow process self (netlink_audit_socket (nlmsg_relay))

      Without this policy, any attempt to relay network debug messages is blocked. This might fill the node’s audit logs with SELinux denials.

  • The following policies allow libvirtd to access hugetblfs, which is required to support huge pages:

    • allow process hugetlbfs_t (dir (add_name create write remove_name rmdir setattr))

    • allow process hugetlbfs_t (file (create unlink))

  • The following policies allow virtiofs to mount filesystems and access NFS:

    • allow process nfs_t (dir (mounton))

    • allow process proc_t (dir (mounton))

    • allow process proc_t (filesystem (mount unmount))

Additional OpenShift Container Platform security context constraints and Linux capabilities for the kubevirt-controller service account

Security context constraints (SCCs) control permissions for pods. These permissions include actions that a pod, a collection of containers, can perform and what resources it can access. You can use SCCs to define a set of conditions that a pod must run with to be accepted into the system.

The virt-controller is a cluster controller that creates the virt-launcher pods for virtual machines in the cluster. These pods are granted permissions by the kubevirt-controller service account.

The kubevirt-controller service account is granted additional SCCs and Linux capabilities so that it can create virt-launcher pods with the appropriate permissions. These extended permissions allow virtual machines to use OpenShift Virtualization features that are beyond the scope of typical pods.

The kubevirt-controller service account is granted the following SCCs:

  • scc.AllowHostDirVolumePlugin = true
    This allows virtual machines to use the hostpath volume plugin.

  • scc.AllowPrivilegedContainer = false
    This ensures the virt-launcher pod is not run as a privileged container.

  • scc.AllowedCapabilities = []corev1.Capability{"SYS_NICE", "NET_BIND_SERVICE", "SYS_PTRACE"}

    • SYS_NICE allows setting the CPU affinity.

    • NET_BIND_SERVICE allows DHCP and Slirp operations.

    • SYS_PTRACE enables certain versions of libvirt to find the process ID (PID) of swtpm, a software Trusted Platform Module (TPM) emulator.

Viewing the SCC and RBAC definitions for the kubevirt-controller

You can view the SecurityContextConstraints definition for the kubevirt-controller by using the oc tool:

$ oc get scc kubevirt-controller -o yaml

You can view the RBAC definition for the kubevirt-controller clusterrole by using the oc tool:

$ oc get clusterrole kubevirt-controller -o yaml