kyverno/examples/best_practices/policy_validate_deny_runasrootuser.yaml

apiVersion: kyverno.io/v1alpha1
kind: ClusterPolicy
metadata:
  name: validate-deny-runasrootuser
spec:
  validationFailureAction: "audit"
  rules:
  - name: deny-runasrootuser
    exclude:
      resources:
        namespaces: 
        - kube-system
    match:
      resources:
        kinds:
        - Pod
    validate:
      message: "Root user is not allowed. Set runAsNonRoot to true."
      anyPattern:
      - spec:
          securityContext:
            runAsNonRoot: true
      - spec:
          containers:
          - name: "*"
            securityContext:
              runAsNonRoot: true