flask/policy: split out rules for system_r

When the all_system_role module is enabled, any domain type can be
created using the system_r role, which was the default.  When it is
disabled, domains not using the default types (dom0_t and domU_t) must
use another role such as vm_r.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>

tools/flask/policy/modules/all_system_role.te

@@ -0,0 +1,8 @@
+# Allow all domains to use system_r so that systems that are not using the
+# user/role separation feature will work properly.
+role system_r types domain_type;
+
+# The vm role is used as part of user separation.  Allow all domain types to use
+# this role except dom0.
+role vm_r;
+role vm_r types { domain_type -dom0_t };

tools/flask/policy/modules/domU.te

@@ -23,3 +23,6 @@ make_device_model(dom0_t, dm_dom_t, domU_t)
 
 # This is required for PCI (or other device) passthrough
 delegate_devices(dom0_t, domU_t)
+
+# Both of these domain types can be created using the default (system) role
+role system_r types { domU_t dm_dom_t };

tools/flask/policy/modules/modules.conf

@@ -32,3 +32,8 @@ nomigrate = on
 
 # Example device policy.  Also see policy/device_contexts.
 nic_dev = on
+
+# This allows any domain type to be created using the system_r role.  When it is
+# disabled, domains not using the default types (dom0_t and domU_t) must use
+# another role (such as vm_r) from the vm_role module.
+all_system_role = on

tools/flask/policy/modules/xen.te

@@ -78,12 +78,7 @@ neverallow * ~event_type:event { create send status };
 # The object role (object_r) is used for devices, resources, and event channels;
 # it does not need to be defined here and should not be used for domains.
 
-# The system role is used for utility domains and pseudo-domains
+# The system role is used for utility domains and pseudo-domains.  If roles are
+# not being used for separation, all domains can use the system role.
 role system_r;
-role system_r types { xen_type domain_type };
-# If you want to prevent domUs from being placed in system_r:
-##role system_r types { xen_type dom0_t };
-
-# The vm role is used for customer virtual machines
-role vm_r;
-role vm_r types { domain_type -dom0_t };
+role system_r types { xen_type dom0_t };