kyverno/examples/best_practices/policy_validate_image_registries.yaml

apiVersion : kyverno.io/v1alpha1
kind: ClusterPolicy
metadata:
  name: validate-image-registry
spec:
  rules:
  - name: validate-image-registry
    match:
      resources:
        kinds:
        - Pod
    validate:
      message: "Image registry is not allowed"
      pattern:
        spec:
          containers:
          - name: "*"
            # Check allowed registries
            image: "*nirmata* | https://private.registry.io/*"