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genpolicy-advanced-command-line-parameters.md

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Agent Policy generation tool - advanced command line parameters

See genpolicy for general information about the Kata Agent Policy generation tool.

Basic genpolicy usage

The most basic way to use genpolicy is to provide just a Kubernetes YAML file as command line parameter - e.g.,

$ genpolicy -y test.yaml

genpolicy encodes the auto-generated Policy text in base64 format and appends the encoded string as an annotation to user's YAML file.

Enable genpolicy logging

genpolicy is using standard Rust logging. To enable logging, use the RUST_LOG environment variable - e.g.,

$ RUST_LOG=info genpolicy -y test.yaml

or

$ RUST_LOG=debug genpolicy -y test.yaml

RUST_LOG=debug logs are more detailed than the RUST_LOG=info logs.

Cache container image information

See genpolicy Policy details for information regarding the contents of the auto-generated Policy. Part of the Policy contents is information used to verify the integrity of container images. In order to calculate the image integrity information, genpolicy needs to download the container images referenced by the YAML file. For example, when specifying the following YAML file as parameter:

apiVersion: v1
kind: Pod
metadata:
  name: policy-test
spec:
  runtimeClassName: kata
  containers:
    - name: first-test-container
      image: quay.io/prometheus/busybox:latest
      command:
        - sleep
        - "120"

genpolicy downloads the quay.io/prometheus/busybox:latest container image.

Depending on the size of the container images and the speed of the network connection to the container registry, downloading these images might take several minutes. For testing scenarios where genpolicy gets executed several times, it can be useful to cache the container images after downloading them, in order to avoid most of the time needed to download the same container images multiple times. If a container image layer was already cached locally, genpolicy uses the local copy of that container layer. The application caches the image information under the ./layers_cache directory.

Warning Using cached image layers can lead to undesirable results. For example, if one or more locally cached layers have been modified (e.g., by an attacker) then the auto-generated Policy will allow those modified container images to be executed on the Guest VM.

To enable caching, use the -u command line parameter - e.g.,

$ RUST_LOG=info genpolicy -u -y test.yaml

Use containerd to pull and manage images

You may specify -d to use existing containerd installation as image manager. This method supports a wider set of images (e.g., older images with v1 manifest). Needs sudo permission to access socket - e.g.,

$ sudo genpolicy -d -y test.yaml

This will use /var/contaienrd/containerd.sock as default socket path. Or you may specify your own socket path - e.g.,

$ sudo genpolicy -d=/my/path/containerd.sock -y test.yaml

Print the Policy text

To print the auto-generated Policy text, in addition to adding its base64 encoding into the YAML file, specify the -r parameter - e.g.,

$ genpolicy -r -y test.yaml

Print the base64 encoded Policy

To print the base64 encoded Policy, in addition to adding it into the YAML file, specify the -b parameter - e.g.,

$ genpolicy -b -y test.yaml

Use a custom genpolicy settings file

The default genpolicy settings file is ./genpolicy-settings.json. Users can specify in the command line a different settings file by using the -j parameter - e.g.,

$ genpolicy -j my-settings.json -y test.yaml

Use a custom path to genpolicy input files

By default, the genpolicy input files rules.rego and genpolicy-settings.json must be present in the current directory - otherwise genpolicy returns an error. Users can specify different paths to these two files, using the -p and -j command line parameters - e.g.,

$ genpolicy -p /tmp/rules.rego -j /tmp/genpolicy-settings.json -y test.yaml

Silently ignore unsupported input YAML fields

As described by the Kubernetes docs, K8s supports a very large number of fields in YAML files. genpolicy supports just a subset of these fields (hopefully the most commonly used fields!). The genpolicy authors reviewed the YAML fields that are supported as inputs to this tool, and evaluated the impact of each field for confidential containers. Some other input fields were not evaluated and/or don't make much sense when present in an input YAML file. By default, when genpolicy encounters an unsupported field in its input YAML file, the application returns an error.

For example, when the input YAML contains:

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: "2023-09-18T23:08:02Z"

genpolicy returns an error, because:

  1. Specifying a fixed creation timestamp as input for a pod doesn't seem very helpful.
  2. The genpolicy authors did not evaluate the potential effects of this field when creating a confidential containers pod.

Users can choose to silently ignore unsupported fields by using the -s parameter:

$ genpolicy -s -y test.yaml

Warning Ignoring unsupported input YAML fields can result in generating an unpredictably incorrect Policy. The -s parameter should be used just by expert K8s and confidential container users, and only after they carefully evaluate the effects of ignoring these fields.

Tip The -s parameter can be helpful for example when investigating a problem related to an already created Kubernetes pod - e.g.,:

  1. Obtain the existing pod YAML from Kubernetes:
kubectl get pod my-pod -o yaml > my-pod.yaml
  1. Auto-generate a Policy corresponding to that YAML file:
$ genpolicy -s -y my-pod.yaml

Specify an input ConfigMap YAML file

genpolicy doesn't attach a Policy to ConfigMap YAML files. However, a ConfigMap YAML file might be required for generating a reasonable Policy for other types of YAML files.

For example, given just this Pod input file (test.yaml):

apiVersion: v1
kind: Pod
metadata:
  name: policy-test
spec:
  runtimeClassName: kata
  containers:
    - name: first-test-container
      image: quay.io/prometheus/busybox:latest
      command:
        - sleep
        - "120"
      env:
        - name: CONFIG_MAP_VALUE1
          valueFrom:
            configMapKeyRef:
              key: simple_value1
              name: config-map1

genpolicy is not able to generate the Policy data used to verify the expected value of the CONFIG_MAP_VALUE1 environment variable. There are two ways to specify the required ConfigMap information:

Specify a ConfigMap input YAML file in the command line

A user can create for example test-config.yaml with the following contents:

apiVersion: v1
kind: ConfigMap
metadata:
  name: config-map1
data:
  simple_value1: value1

and specify that file in the genpolicy command line using the -c parameter:

$ genpolicy -c test-config.yaml -y test.yaml

Add the ConfigMap information into the input YAML file

The same ConfigMap information above can be added to test.yaml:

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: config-map1
data:
  simple_value1: value1
---
apiVersion: v1
kind: Pod
metadata:
  name: policy-test
spec:
  runtimeClassName: kata
  containers:
    - name: first-test-container
      image: quay.io/prometheus/busybox:latest
      command:
        - sleep
        - "120"
      env:
        - name: CONFIG_MAP_VALUE1
          valueFrom:
            configMapKeyRef:
              key: simple_value1
              name: config-map1

and then the -c parameter is no longer needed:

$ genpolicy -y test.yaml