Add dedicated seccomp node reference

Signed-off-by: Sascha Grunert <[email protected]>

content/en/docs/concepts/security/linux-kernel-security-constraints.md

@@ -90,7 +90,8 @@ profile to a more permissive profile.
 {{</note>}}
 
 To learn how to implement seccomp in Kubernetes, refer to
-[Restrict a Container's Syscalls with seccomp](/docs/tutorials/security/seccomp/).
+[Restrict a Container's Syscalls with seccomp](/docs/tutorials/security/seccomp/)
+or the [Seccomp node reference](/docs/reference/node/seccomp/)
 
 To learn more about seccomp, see
 [Seccomp BPF](https://www.kernel.org/doc/html/latest/userspace-api/seccomp_filter.html)
@@ -288,3 +289,4 @@ of support that you need. For instructions, refer to
 * [Learn how to use AppArmor](/docs/tutorials/security/apparmor/)
 * [Learn how to use seccomp](/docs/tutorials/security/seccomp/)
 * [Learn how to use SELinux](/docs/tasks/configure-pod-container/security-context/#assign-selinux-labels-to-a-container)
+* [Seccomp Node Reference](/docs/reference/node/seccomp/)

content/en/docs/reference/node/_index.md

@@ -15,6 +15,8 @@ This section contains the following reference topics about nodes:
 
 * [Node `.status` information](/docs/reference/node/node-status/)
 
+* [Seccomp information](/docs/reference/node/seccomp/)
+
 You can also read node reference details from elsewhere in the
 Kubernetes documentation, including:
 

content/en/docs/reference/node/seccomp.md

@@ -0,0 +1,119 @@
+---
+content_type: reference
+title: Seccomp and Kubernetes
+weight: 80
+---
+
+<!-- overview -->
+
+Seccomp stands for secure computing mode and has been a feature of the Linux
+kernel since version 2.6.12. It can be used to sandbox the privileges of a
+process, restricting the calls it is able to make from userspace into the
+kernel. Kubernetes lets you automatically apply seccomp profiles loaded onto a
+{{< glossary_tooltip text="node" term_id="node" >}} to your Pods and containers.
+
+## Seccomp fields
+
+{{< feature-state for_k8s_version="v1.19" state="stable" >}}
+
+There are four ways to specify a seccomp profile for a
+{{< glossary_tooltip text="pod" term_id="pod" >}}:
+
+- for the whole Pod using [`spec.securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context)
+- for a single container using [`spec.containers[*].securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context-1)
+- for an (restartable / sidecar) init container using [`spec.initContainers[*].securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context-1)
+- for an [ephermal container](/docs/concepts/workloads/pods/ephemeral-containers) using [`spec.ephemeralContainers[*].securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context-2)
+
+{{% code_sample file="pods/security/seccomp/fields.yaml" %}}
+
+The Pod in the example above runs as `Unconfined`, while the
+`ephemeral-container` and `init-container` specifically defines
+`RuntimeDefault`. If the ephemeral or init container would not have set the
+`securityContext.seccompProfile` field explicitly, then the value would be
+inherited by the Pod. The same applies to the container, which runs a
+`Localhost` profile `my-profile.json`.
+
+Generally speaking, fields from (ephemeral) containers have a higher priority
+than the Pod level value, while containers which do not set the seccomp field
+are being inherited by the Pod.
+
+{{< note >}}
+It is not possible to apply a seccomp profile to a Pod or container running with
+`privileged: true` set in the container's `securityContext`. Privileged
+containers always run as `Unconfined`.
+{{< /note >}}
+
+The following values are possible for the `seccompProfile.type`:
+
+`Unconfined`
+: The workload runs without any seccomp restrictions.
+
+`RuntimeDefault`
+: A default seccomp profile defined by the {{< glossary_tooltip text="container runtime" term_id="container-runtime" >}} is applied.
+
+`Localhost`
+: The `localhostProfile` will be applied, which has to be available on the node disk (on Linux it's `/var/lib/kubelet/seccomp`).
+
+### `Localhost` profiles
+
+Seccomp profiles are JSON files following the scheme defined by the
+[OCI runtime specification](https://github.com/opencontainers/runtime-spec/blob/f329913/config-linux.md#seccomp).
+A profile basically defines actions based on matched syscalls, but also allows
+to pass specific values as arguments to syscalls. For example:
+
+{{% code_sample file="pods/security/seccomp/profile.json" %}}
+
+The `defaultAction` in the profile above is defined as `SCMP_ACT_ERRNO` and
+should return on every not matching syscall of `syscalls.names`. The error is
+defined as code `38` via the `defaultErrnoRet` field.
+
+The following actions are generally possible:
+
+`SCMP_ACT_ERRNO`
+: Return the specified error code.
+
+`SCMP_ACT_ALLOW`
+: Allow the syscall to be executed.
+
+`SCMP_ACT_KILL_PROCESS`
+: Kill the process.
+
+`SCMP_ACT_KILL_THREAD` and `SCMP_ACT_KILL`
+: Kill only the thread.
+
+`SCMP_ACT_TRAP`
+: Throw a `SIGSYS` signal.
+
+`SCMP_ACT_NOTIFY` and `SECCOMP_RET_USER_NOTIF`.
+: Notify the user space.
+
+`SCMP_ACT_TRACE`
+: Notify a tracing process with the specified value.
+
+`SCMP_ACT_LOG`
+: Allow the syscall to be executed after the action has been logged to syslog or auditd.
+
+Some actions like `SCMP_ACT_NOTIFY` or `SECCOMP_RET_USER_NOTIF` may be not
+supported depending on the container runtime, OCI runtime or Linux kernel
+version being used. There may be also further limitations, for example that
+`SCMP_ACT_NOTIFY` cannot be used as `defaultAction` or for certain syscalls like
+`write`. All those limitations are defined by either the OCI runtime
+([runc](https://github.com/opencontainers/runc),
+[crun](https://github.com/containers/crun)) or
+[libseccomp](https://github.com/seccomp/libseccomp).
+
+The `syscalls` JSON array contains a list of objects referencing syscalls by
+their respective `names`. In the above example the list of syscalls to be
+allowed is using the action `SCMP_ACT_ALLOW`. It would also be possible to
+define another list using the action `SCMP_ACT_ERRNO` but a different return
+(`errnoRet`) value.
+
+It is also possible to specify the arguments (`args`) passed to certain
+syscalls. More information about those advanced use cases can be found in the
+[OCI runtime spec](https://github.com/opencontainers/runtime-spec/blob/f329913/config-linux.md#seccomp)
+and the [Seccomp Linux kernel documentation](https://www.kernel.org/doc/Documentation/prctl/seccomp_filter.txt).
+
+## Further reading
+
+- [Restrict a Container's Syscalls with seccomp](/docs/tutorials/security/seccomp/)
+- [Pod Security Standards](/docs/concepts/security/pod-security-standards/)

content/en/docs/tasks/administer-cluster/securing-a-cluster.md

@@ -275,3 +275,4 @@ page for more on how to report vulnerabilities.
 ## What's next
 
 - [Security Checklist](/docs/concepts/security/security-checklist/) for additional information on Kubernetes security guidance.
+- [Seccomp Node Reference](/docs/reference/node/seccomp/)

content/en/examples/pods/security/seccomp/fields.yaml

@@ -0,0 +1,27 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: pod
+spec:
+  securityContext:
+    seccompProfile:
+      type: Unconfined
+  ephemeralContainers:
+  - name: ephemeral-container
+    image: debian
+    securityContext:
+      seccompProfile:
+        type: RuntimeDefault
+  initContainers:
+  - name: init-container
+    image: debian
+    securityContext:
+      seccompProfile:
+        type: RuntimeDefault
+  containers:
+  - name: container
+    image: docker.io/library/debian:stable
+    securityContext:
+      seccompProfile:
+        type: Localhost
+        localhostProfile: my-profile.json

content/en/examples/pods/security/seccomp/profile.json

@@ -0,0 +1,18 @@
+{
+  "defaultAction": "SCMP_ACT_ERRNO",
+  "defaultErrnoRet": 38,
+  "syscalls": [
+    {
+      "names": [
+        "adjtimex",
+        "alarm",
+        "bind",
+        "waitid",
+        "waitpid",
+        "write",
+        "writev"
+      ],
+      "action": "SCMP_ACT_ALLOW"
+    }
+  ]
+}