apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: require-readonly-root-filesystem
  annotations:
    policies.kyverno.io/title: Require Read-Only Root Filesystem
    policies.kyverno.io/category: Pod Security
    policies.kyverno.io/severity: high
spec:
  validationFailureAction: Audit
  background: true

  rules:
    - name: require-readonly-root-filesystem
      match:
        any:
          - resources:
              kinds:
                - Pod

      validate:
        message: "Containers must use readOnlyRootFilesystem=true."

        foreach:
          - list: "request.object.spec.containers"
            pattern:
              securityContext:
                readOnlyRootFilesystem: true

          - list: "request.object.spec.initContainers"
            pattern:
              securityContext:
                readOnlyRootFilesystem: true

          - list: "request.object.spec.ephemeralContainers"
            pattern:
              securityContext:
                readOnlyRootFilesystem: true