kyverno/samples/best_practices/disallow_root_user.yaml

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: disallow-root-user
  annotations:
    policies.kyverno.io/category: Security
    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:
  rules:
  - name: validate-runAsNonRoot
    match:
      resources:
        kinds:
        - Pod
    validate:
      message: "Running as root user is not allowed. Set runAsNonRoot to true"
      anyPattern:
      - spec:
          securityContext:
            # https://github.com/kubernetes/api/blob/7dc09db16fb8ff2eee16c65dc066c85ab3abb7ce/core/v1/types.go#L3165
            runAsNonRoot: true
      - spec:
          containers:
          - securityContext:
              # https://github.com/kubernetes/api/blob/7dc09db16fb8ff2eee16c65dc066c85ab3abb7ce/core/v1/types.go#L5742
              runAsNonRoot: true