Use encrypted container images (sc2-sys#20)

apps/helloworld-knative-encrypted/service.yaml

@@ -0,0 +1,24 @@
+apiVersion: serving.knative.dev/v1
+kind: Service
+metadata:
+  name: helloworld-knative
+  annotations:
+    "features.knative.dev/podspec-runtimeclassname": "enabled"
+spec:
+  template:
+    metadata:
+      labels:
+        apps.coco-serverless/name: helloworld-py
+        io.katacontainers.config.pre_attestation.enabled: "false"
+    spec:
+      runtimeClassName: kata-qemu-sev
+      # coco-knative: need to run user container as root
+      securityContext:
+        runAsUser: 1000
+      containers:
+        - image: csegarragonz/coco-helloworld-py:encrypted
+          ports:
+            - containerPort: 8080
+          env:
+            - name: TARGET
+              value: "World"

conf-files/ocicrypt.conf

@@ -0,0 +1,7 @@
+{
+  "key-providers": {
+    "attestation-agent": {
+      "grpc": "127.0.0.1:50000"
+    }
+  }
+}

docs/helloworld_knative_attestation.md

@@ -19,9 +19,15 @@ following subsections (in increasing order of security):
 with the right firmware, kernel, initrd, and Kata Agent configuration.
 * [Signed Container Images](#signed-container-images) - Attest that the images
 used have been signed with a well-known private key.
+* [Encrypted Container Images](#encrypted-container-images) - In addition to
+signatures, consume encrypted container images.
 
 After that, you may jump to [running the application](#run-the-application).
 
+> Note that, if you are running different attestation types one after the other
+> you may want to clear the contents of the KBS between runs using:
+> `inv kbs.clear-db`
+
 ## Firmware Digest
 
 Before running the application, we need to generate the expected launch digest
@@ -109,6 +115,31 @@ Now, you may proceed to [running the application](#run-the-application).
 
 ## Encrypted Container Images
 
+In this last section, we will configure the system to consume encrypted
+container images from public registries.
+
+To encrypt docker images, we use [`skopeo`](https://github.com/containers/skopeo).
+`skopeo` can be used together with image signatures, just make sure to pass the
+`--sign` flag:
+
+```bash
+inv skopeo.encrypt-container-image "docker.io/csegarragonz/coco-helloworld-py:unencrypted" --sign
+```
+
+> To check that the image is actually encrypted, you may try to run it:
+> `docker run docker.io/csegarragonz/coco-helloworld-py:encrypted`
+
+Then, as in the previous section, update the KBS to set the right signature
+verification policy:
+
+```bash
+# IMPORTANT: do not use the `--clean` flag here, as the encrypt-container-image
+# command will provision a secret to the KBS
+inv kbs.provision-launch-digest --signature-policy verify
+```
+
+Finally, you may proceed to [running the application](#run-the-application).
+
 ## Run the application
 
 Once the KBS has been populated with the right measurements and secrets, we can
@@ -117,3 +148,9 @@ deploy the workload just like with the `Hello world! (Knative)` app:
 ```bash
 kubectl apply -f ./apps/helloworld-knative
 ```
+
+note that if you are using encrypted images you will have to do:
+
+```bash
+kubectl apply -f ./apps/helloworld-knative-encrypted
+```

tasks/__init__.py

@@ -13,6 +13,7 @@
 from . import kubeadm
 from . import operator
 from . import sev
+from . import skopeo
 
 ns = Collection(
     apps,
@@ -28,4 +29,5 @@
     kubeadm,
     operator,
     sev,
+    skopeo,
 )

tasks/coco.py

@@ -1,7 +1,6 @@
 from invoke import task
 from os.path import join
-from tasks.util.env import KATA_CONFIG_DIR
-from tasks.util.kbs import KBS_PORT, get_kbs_url
+from tasks.util.env import KATA_CONFIG_DIR, KBS_PORT, get_kbs_url
 from tasks.util.toml import read_value_from_toml, update_toml
 
 

tasks/kbs.py

@@ -1,19 +1,16 @@
-from base64 import b64encode
 from invoke import task
-from os.path import exists, join
+from os.path import exists
 from subprocess import run
 from tasks.util.cosign import COSIGN_PUB_KEY
 from tasks.util.kbs import (
-    NO_SIGNATURE_POLICY,
     SIMPLE_KBS_DIR,
-    SIMPLE_KBS_RESOURCE_PATH,
     SIGNATURE_POLICY_NONE,
     create_kbs_resource,
     connect_to_kbs_db,
     populate_signature_verification_policy,
+    set_launch_measurement_policy,
     validate_signature_verification_policy,
 )
-from tasks.util.sev import get_launch_digest
 
 SIGNATURE_POLICY_STRING_ID = "default/security-policy/test"
 
@@ -74,7 +71,7 @@ def clear_db(ctx):
 
 
 @task
-def provision_launch_digest(ctx, signature_policy=NO_SIGNATURE_POLICY, clean=False):
+def provision_launch_digest(ctx, signature_policy=SIGNATURE_POLICY_NONE, clean=False):
     """
     Provision the KBS with the launch digest for the current node
 
@@ -101,85 +98,52 @@ def provision_launch_digest(ctx, signature_policy=NO_SIGNATURE_POLICY, clean=Fal
     if clean:
         clear_db(ctx)
 
-    # First, add our launch digest to the KBS policy
-    ld = get_launch_digest("sev")
-    ld_b64 = b64encode(ld).decode()
-
-    # Create a new record
-    connection = connect_to_kbs_db()
-    with connection:
-        with connection.cursor() as cursor:
-            policy_id = 10
-
-            # When enabling signature verification, we need to provide a
-            # signature policy. This policy has a constant string identifier
-            # that the kata agent will ask for (default/security-policy/test),
-            # which points to a config file that specifies how to validate
-            # signatures
-            if signature_policy != NO_SIGNATURE_POLICY:
-                resource_path = "signature_policy_{}.json".format(signature_policy)
-
-                if signature_policy == SIGNATURE_POLICY_NONE:
-                    # If we set a `none` signature policy, it means that we don't
-                    # check any signatures on the pulled container images
-                    policy_json_str = populate_signature_verification_policy(
-                        signature_policy
-                    )
-                else:
-                    # The verify policy, checks that the image has been signed
-                    # with a given key. As everything in the KBS, the key
-                    # we give in the policy is an ID for another resource.
-                    # Note that the following resource prefix is NOT required
-                    # (i.e. we could change it to keys/cosign/1 as long as the
-                    # corresponding resource exists)
-                    signing_key_resource_id = "default/cosign-key/1"
-                    policy_json_str = populate_signature_verification_policy(
-                        signature_policy,
-                        [
-                            [
-                                "docker.io/csegarragonz/coco-helloworld-py",
-                                signing_key_resource_id,
-                            ],
-                            [
-                                "docker.io/csegarragonz/coco-knative-sidecar",
-                                signing_key_resource_id,
-                            ],
-                        ],
-                    )
-
-                    # Create a resource for the signing key
-                    signing_key_kbs_path = "cosign.pub"
-                    signing_key_resource_path = join(
-                        SIMPLE_KBS_RESOURCE_PATH, signing_key_kbs_path
-                    )
-                    sql = "INSERT INTO resources VALUES(NULL, NULL, "
-                    sql += "'{}', '{}', {})".format(
-                        signing_key_resource_id, signing_key_kbs_path, policy_id
-                    )
-                    cursor.execute(sql)
-
-                    # Lastly, we copy the public signing key to the resource
-                    # path annotated in the policy
-                    cp_cmd = "cp {} {}".format(
-                        COSIGN_PUB_KEY, signing_key_resource_path
-                    )
-                    run(cp_cmd, shell=True, check=True)
-
-                create_kbs_resource(resource_path, policy_json_str)
-
-            # Create the resource (containing the signature policy) in the KBS
-            sql = "INSERT INTO resources VALUES(NULL, NULL, "
-            sql += "'{}', '{}', {})".format(
-                SIGNATURE_POLICY_STRING_ID, resource_path, policy_id
-            )
-            cursor.execute(sql)
-
-            # We associate the signature policy to a digest policy, meaning
-            # that irrespective of what signature policy are we using (even if
-            # we are not checking any signatures) we will always check the FW
-            # digest against the measured one
-            sql = "INSERT INTO policy VALUES ({}, ".format(policy_id)
-            sql += "'[\"{}\"]', '[]', 0, 0, '[]', now(), NULL, 1)".format(ld_b64)
-            cursor.execute(sql)
-
-        connection.commit()
+    # First, we provision a launch digest policy that only allows to
+    # boot confidential VMs with the launch measurement that we have
+    # just calculated. We will associate signature verification and
+    # image encryption policies to this launch digest policy.
+    set_launch_measurement_policy()
+
+    # To make sure the launch policy is enforced, we must enable
+    # signature verification. This means that we also need to provide a
+    # signature policy. This policy has a constant string identifier
+    # that the kata agent will ask for (default/security-policy/test),
+    # which points to a config file that specifies how to validate
+    # signatures
+    resource_path = "signature_policy_{}.json".format(signature_policy)
+
+    if signature_policy == SIGNATURE_POLICY_NONE:
+        # If we set a `none` signature policy, it means that we don't
+        # check any signatures on the pulled container images (still
+        # necessary to set the policy to check the launch measurment)
+        policy_json_str = populate_signature_verification_policy(signature_policy)
+    else:
+        # The verify policy, checks that the image has been signed
+        # with a given key. As everything in the KBS, the key
+        # we give in the policy is an ID for another resource.
+        # Note that the following resource prefix is NOT required
+        # (i.e. we could change it to keys/cosign/1 as long as the
+        # corresponding resource exists)
+        signing_key_resource_id = "default/cosign-key/1"
+        policy_json_str = populate_signature_verification_policy(
+            signature_policy,
+            [
+                [
+                    "docker.io/csegarragonz/coco-helloworld-py",
+                    signing_key_resource_id,
+                ],
+                [
+                    "docker.io/csegarragonz/coco-knative-sidecar",
+                    signing_key_resource_id,
+                ],
+            ],
+        )
+
+        # Create a resource for the signing key
+        with open(COSIGN_PUB_KEY) as fh:
+            create_kbs_resource(signing_key_resource_id, "cosign.pub", fh.read())
+
+    # Finally, create a resource for the image signing policy. Note that the
+    # resource ID for the image signing policy is hardcoded in the kata agent
+    # (particularly in the attestation agent)
+    create_kbs_resource(SIGNATURE_POLICY_STRING_ID, resource_path, policy_json_str)

tasks/skopeo.py

@@ -0,0 +1,103 @@
+from base64 import b64encode
+from invoke import task
+from json import loads as json_loads
+from os.path import exists, join
+from subprocess import run
+from tasks.util.cosign import sign_container_image
+from tasks.util.env import CONF_FILES_DIR, K8S_CONFIG_DIR
+from tasks.util.guest_components import (
+    start_coco_keyprovider,
+    stop_coco_keyprovider,
+)
+from tasks.util.kbs import create_kbs_secret
+
+SKOPEO_VERSION = "1.13.0"
+SKOPEO_IMAGE = "quay.io/skopeo/stable:v{}".format(SKOPEO_VERSION)
+SKOPEO_ENCRYPTION_KEY = join(K8S_CONFIG_DIR, "image_enc.key")
+AA_CTR_ENCRYPTION_KEY = "/tmp/image_enc.key"
+
+
+def run_skopeo_cmd(cmd, capture_stdout=False):
+    ocicrypt_conf_host = join(CONF_FILES_DIR, "ocicrypt.conf")
+    ocicrypt_conf_guest = "/ocicrypt.conf"
+    skopeo_cmd = [
+        "docker run --rm",
+        "--net host",
+        "-e OCICRYPT_KEYPROVIDER_CONFIG={}".format(ocicrypt_conf_guest),
+        "-v {}:{}".format(ocicrypt_conf_host, ocicrypt_conf_guest),
+        "-v ~/.docker/config.json:/config.json",
+        SKOPEO_IMAGE,
+        cmd,
+    ]
+    skopeo_cmd = " ".join(skopeo_cmd)
+    if capture_stdout:
+        return (
+            run(skopeo_cmd, shell=True, capture_output=True)
+            .stdout.decode("utf-8")
+            .strip()
+        )
+    else:
+        run(skopeo_cmd, shell=True, check=True)
+
+
+def create_encryption_key():
+    cmd = "head -c32 < /dev/random > {}".format(SKOPEO_ENCRYPTION_KEY)
+    run(cmd, shell=True, check=True)
+
+
+@task
+def encrypt_container_image(ctx, image_tag, sign=False):
+    """
+    Encrypt an OCI container image using Skopeo
+
+    The image tag must be provided in the format: docker.io/<repo>/<name>:tag
+    """
+    encryption_key_resource_id = "default/image-encryption-key/1"
+    if not exists(SKOPEO_ENCRYPTION_KEY):
+        create_encryption_key()
+
+    # We use CoCo's keyprovider server (that implements the ocicrypt protocol)
+    # to encrypt the OCI image. To that extent, we need to mount the encryption
+    # key somewhere that the attestation agent (in the keyprovider) can find
+    # it
+    start_coco_keyprovider(SKOPEO_ENCRYPTION_KEY, AA_CTR_ENCRYPTION_KEY)
+
+    encrypted_image_tag = image_tag.split(":")[0] + ":encrypted"
+    skopeo_cmd = [
+        "copy --insecure-policy",
+        "--authfile /config.json",
+        "--encryption-key",
+        "provider:attestation-agent:keyid=kbs:///{}::keypath={}".format(
+            encryption_key_resource_id, AA_CTR_ENCRYPTION_KEY
+        ),
+        "docker://{}".format(image_tag),
+        "docker://{}".format(encrypted_image_tag),
+    ]
+    skopeo_cmd = " ".join(skopeo_cmd)
+    run_skopeo_cmd(skopeo_cmd)
+
+    # Sanity check that the image is actually encrypted
+    inspect_jsonstr = run_skopeo_cmd(
+        "inspect docker://{}".format(encrypted_image_tag), capture_stdout=True
+    )
+    inspect_json = json_loads(inspect_jsonstr)
+    layers = [
+        layer["MIMEType"].endswith("tar+gzip+encrypted")
+        for layer in inspect_json["LayersData"]
+    ]
+    if not all(layers):
+        print("Some layers in image {} are not encrypted!".format(encrypted_image_tag))
+        stop_coco_keyprovider()
+        raise RuntimeError("Image encryption failed!")
+
+    # Create a secret in KBS with the encryption key. Skopeo needs it as raw
+    # bytes, whereas KBS wants it base64 encoded, so we do the conversion first
+    with open(SKOPEO_ENCRYPTION_KEY, "rb") as fh:
+        key_b64 = b64encode(fh.read()).decode()
+
+    create_kbs_secret(encryption_key_resource_id, key_b64)
+
+    if sign:
+        sign_container_image(encrypted_image_tag)
+
+    stop_coco_keyprovider()