apiVersion: admissionregistration.k8s.io/v1alpha1
kind: ValidatingAdmissionPolicy
metadata:
  name: "disallow-host-path"
spec:
  matchConstraints:
    resourceRules:
    - apiGroups:   [""]
      apiVersions: ["v1"]
      operations:  ["CREATE", "UPDATE"]
      resources:   ["pods"]
  validations:
    - expression: "!has(object.spec.volumes) || object.spec.volumes.all(volume, !has(volume.hostPath))"
      message: "HostPath volumes are forbidden. The field spec.volumes[*].hostPath must be unset."