Add Pod Security Standards documentation

content/en/docs/concepts/security/overview.md

@@ -2,8 +2,10 @@
 reviewers:
 - zparnold
 title: Overview of Cloud Native Security
+description: >
+  A model for thinking about Kubernetes security in the context of Cloud Native security.
 content_type: concept
-weight: 10
+weight: 1
 ---
 
 <!-- overview -->

content/en/docs/concepts/security/pod-security-admission.md

@@ -0,0 +1,129 @@
+---
+reviewers:
+- tallclair
+- liggitt
+title: Pod Security Admission
+description: >
+  An overview of the Pod Security Admission Controller, which can enforce the Pod Security
+  Standards.
+content_type: concept
+weight: 20
+min-kubernetes-server-version: v1.22
+---
+
+<!-- overview -->
+
+{{< feature-state for_k8s_version="v1.22" state="alpha" >}}
+
+The Kubernetes [Pod Security Standards](/docs/concepts/security/pod-security-standards/) define
+different isolation levels for Pods. These standards let you define how you want to restrict the
+behavior of pods in a clear, consistent fashion.
+
+As an Alpha feature, Kubernetes offers a built-in _Pod Security_ admission plugin, the successor
+to [PodSecurityPolicies](/docs/concepts/policy/pod-security-policy/). Pod security restrictions
+are applied at the {{< glossary_tooltip text="namespace" term_id="namespace" >}} level when pods
+are created.
+
+{{< note >}}
+The PodSecurityPolicy API is deprecated and will be 
+[removed](/docs/reference/using-api/deprecation-guide/#v1-25) from Kubernetes in v1.25.
+{{< /note >}}
+
+<!-- body -->
+
+## Enabling the Alpha feature
+
+Setting pod security controls by namespace is an alpha feature. You must enable the `PodSecurity`
+[feature gate](/docs/reference/command-line-tools-reference/feature-gates/) in order to use it.
+
+```shell
+--feature-gates="...,PodSecurity=true"
+```
+
+## Pod Security Admission configuration for pods
+
+Different policy levels (e.g. `baseline`, `restricted`) have different requirements for
+[Security Context](/docs/tasks/configure-pod-container/security-context/) objects and other related
+fields. Check out the [Pod Security Standards](/docs/concepts/security/pod-security-standards) page
+for an in-depth look at those requirements.
+
+## Pod Security Admission labels for namespaces
+
+Provided that you have enabled this feature, you can configure namespaces to define the admission
+control mode you want to use for pod security in each namespace. Kubernetes defines a set of 
+{{< glossary_tooltip term_id="label" text="labels" >}} that you can set to define which of the 
+predefined Pod Security Standard levels you want to use for a namespace. The label you select
+defines what action the {{< glossary_tooltip text="control plane" term_id="control-plane" >}}
+takes if a potential violation is detected:
+
+{{< table caption="Pod Security Admission modes" >}}
+Mode | Description
+:---------|:------------
+**`enforce`** | Policy violations will cause the pod to be rejected.
+**`audit`** | Policy violations will trigger the addition of an audit annotation, but are otherwise allowed.
+**`warn`** | Policy violations will trigger a user-facing warning, but are otherwise allowed.
+{{< /table >}}
+
+For each mode, there are two labels that you can use:
+
+```yaml
+# The per-mode level label indicates which policy level to apply for the mode.
+#
+# MODE must be one of `enforce`, `audit`, or `warn`.
+# LEVEL must be one of `privileged`, `baseline`, or `restricted`.
+pod-security.kubernetes.io/<MODE>: <LEVEL>
+
+# Optional: per-mode version label that can be used to pin the policy to the
+# version that shipped with a given Kubernetes minor version (e.g. v{{< skew latestVersion >}}).
+#
+# MODE must be one of `enforce`, `audit`, or `warn`.
+# VERSION must be a valid Kubernetes version label.
+pod-security.kubernetes.io/<MODE>-version: <VERSION>
+```
+
+Check out [Enforce Pod Security Standards with Namespace Labels](/docs/tasks/configure-pod-container/enforce-standards-namespace-labels) to see example usage.
+
+## Exemptions
+
+You can define _exemptions_ from pod security enforcement in order allow the creation of pods that
+would have otherwise been prohibited due to the policy associated with a given namespace.
+Exemptions can be statically configured in the
+[Admission Controller configuration](#configuring-the-admission-controller).
+
+Exemptions must be explicitly enumerated, and do not support indirection such as label or group
+selectors. Requests meeting exemption criteria are _ignored_ by the Admission Controller (all
+`enforce`, `audit` and `warn` behaviors), except to record an audit annotation. Exemption
+dimensions include:
+
+- **Usernames:** requests from users with an exempt authenticated (or impersonated) username are
+  ignored.
+- **RuntimeClassNames:** pods and templated pods specifying an exempt runtime class name are
+  ignored.
+- **Namespaces:** pods and templated pods in an exempt namespace are ignored.
+
+The username exemption is special in that the creating user is not persisted on the Pod object,
+and the Pod may be modified by different non-exempt users in the future. Use cases for username
+exemptions include:
+
+- Trusted {{< glossary_tooltip term_id="controller" text="controllers" >}} that create pods.
+- Usernames that represent break-glass operations roles, for example for debugging workloads
+  in a namespace that has restrictions configured. This mechanism only works with a username
+  match; you cannot grant exemptions based on group membership.
+
+Updates to the following pod fields are exempt from policy checks, meaning that if a pod update request only changes these fields, it will not be denied even if the pod is in violation of the current policy level:
+
+- Any metadata updates EXCEPT changes to the seccomp or apparmor annotations:
+  - `seccomp.security.alpha.kubernetes.io/pod` (deprecated)
+  - `container.seccomp.security.alpha.kubernetes.io/*` (deprecated)
+  - `container.apparmor.security.beta.kubernetes.io/*`
+- Valid updates to `.spec.activeDeadlineSeconds`
+- Valid updates to `.spec.tolerations`
+- Valid updates to Pod resources
+
+## {{% heading "whatsnext" %}}
+
+- [Pod Security Standards](/docs/concepts/security/pod-security-standards)
+- [Enforcing Pod Security Standards](/docs/setup/best-practices/enforcing-pod-security-standards)
+- [Enforce Pod Security Standards by Configuring the Built-in Admission Controller](/docs/tasks/configure-pod-container/enforce-standards-admission-controller)
+- [Enforce Pod Security Standards with Namespace Labels](/docs/tasks/configure-pod-container/enforce-standards-namespace-labels)
+- [Migrating from PodSecurityPolicy to PodSecurity](/docs/tasks/secure-pods/migrate-from-psp)