genpolicy: reject untested CreateContainer field values

Reject CreateContainerRequest field values that are not tested by
Kata CI and that might impact the confidentiality of CoCo Guests.

This change uses a "better safe than sorry" approach to untested
fields. It is very possible that in the future we'll encounter
reasonable use cases that will either:

- Show that some of these fields are benign and don't have to be
  verified by Policy, or
- Show that Policy should verify legitimate values of these fields

These are the new CreateContainerRequest Policy rules:

    count(input.shared_mounts) == 0
    is_null(input.string_user)

    i_oci := input.OCI
    is_null(i_oci.Hooks)
    is_null(i_oci.Linux.Seccomp)
    is_null(i_oci.Solaris)
    is_null(i_oci.Windows)

    i_linux := i_oci.Linux
    count(i_linux.GIDMappings) == 0
    count(i_linux.MountLabel) == 0
    count(i_linux.Resources.Devices) == 0
    count(i_linux.RootfsPropagation) == 0
    count(i_linux.UIDMappings) == 0
    is_null(i_linux.IntelRdt)
    is_null(i_linux.Resources.BlockIO)
    is_null(i_linux.Resources.Network)
    is_null(i_linux.Resources.Pids)
    is_null(i_linux.Seccomp)
    i_linux.Sysctl == {}

    i_process := i_oci.Process
    count(i_process.SelinuxLabel) == 0
    count(i_process.User.Username) == 0

Signed-off-by: Dan Mihai <dmihai@microsoft.com>

src/tools/genpolicy/rules.rego

@@ -52,10 +52,15 @@ default WriteStreamRequest := false
 default AllowRequestsFailingPolicy := false
 
 CreateContainerRequest {
+    # Check if the input request should be rejected even before checking the
+    # policy_data.containers information.
+    allow_create_container_input
+
     i_oci := input.OCI
     i_storages := input.storages
     i_devices := input.devices
 
+    # Check if any element from the policy_data.containers array allows the input request.
     some p_container in policy_data.containers
     print("======== CreateContainerRequest: trying next policy container")
 
@@ -85,6 +90,37 @@ CreateContainerRequest {
     print("CreateContainerRequest: true")
 }
 
+allow_create_container_input {
+    print("allow_create_container_input: input =", input)
+
+    count(input.shared_mounts) == 0
+    is_null(input.string_user)
+
+    i_oci := input.OCI
+    is_null(i_oci.Hooks)
+    is_null(i_oci.Solaris)
+    is_null(i_oci.Windows)
+
+    i_linux := i_oci.Linux
+    count(i_linux.GIDMappings) == 0
+    count(i_linux.MountLabel) == 0
+    count(i_linux.Resources.Devices) == 0
+    count(i_linux.RootfsPropagation) == 0
+    count(i_linux.UIDMappings) == 0
+    is_null(i_linux.IntelRdt)
+    is_null(i_linux.Resources.BlockIO)
+    is_null(i_linux.Resources.Network)
+    is_null(i_linux.Resources.Pids)
+    is_null(i_linux.Seccomp)
+    i_linux.Sysctl == {}
+
+    i_process := i_oci.Process
+    count(i_process.SelinuxLabel) == 0
+    count(i_process.User.Username) == 0
+
+    print("allow_create_container_input: true")
+}
+
 # Reject unexpected annotations.
 allow_anno(p_oci, i_oci) {
     print("allow_anno 1: start")