kyverno/samples/best_practices/deny_runasrootuser.yaml

apiVersion: kyverno.io/v1alpha1
kind: ClusterPolicy
metadata:
  name: validate-deny-runasrootuser
  annotations:
    policies.kyverno.io/category: Security Context
    policies.kyverno.io/description: By default, processes in a container run as a 
      root user (uid 0). To prevent potential compromise of container hosts, specify a 
      least privileged user ID when building the container image and require that 
      application containers run as non root users.
spec:
  validationFailureAction: "audit"
  rules:
  - name: deny-runasrootuser
    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