libxl: introduce XSM relabel on build

Allow a domain to be built under one security label and run using a
different label.  This can be used to prevent the domain builder or
control domain from having the ability to access a guest domain's memory
via map_foreign_range except during the build process where this is
required.

Example domain configuration snippet:
  seclabel='customer_1:vm_r:nomigrate_t'
  init_seclabel='customer_1:vm_r:nomigrate_t_building'

Note: this does not provide complete protection from a malicious dom0;
mappings created during the build process may persist after the relabel,
and could be used to indirectly access the guest's memory. However, if
dom0 correctly unmaps the domain upon building, a the domU is protected
against dom0 becoming malicious in the future.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

2 files changed, 53 insertions, 13 deletions

diff --git a/tools/flask/policy/policy/modules/xen/xen.if b/tools/flask/policy/policy/modules/xen/xen.if
index 3f58909b55..2ad11b2206 100644
--- a/tools/flask/policy/policy/modules/xen/xen.if
+++ b/tools/flask/policy/policy/modules/xen/xen.if
@@ -9,24 +9,47 @@
 #   Declare a type as a domain type, and allow basic domain setup
 define(`declare_domain', `
 	type $1, domain_type`'ifelse(`$#', `1', `', `,shift($@)');
+	type $1_channel, event_type;
+	type_transition $1 domain_type:event $1_channel;
 	allow $1 $1:grant { query setup };
 	allow $1 $1:mmu { adjust physmap map_read map_write stat pinpage };
 	allow $1 $1:hvm { getparam setparam };
 ')
 
-# create_domain(priv, target)
-#   Allow a domain to be created
-define(`create_domain', `
+# declare_build_label(type)
+#   Declare a paired _building type for the given domain type
+define(`declare_build_label', `
+	type $1_building, domain_type;
+	type_transition $1_building domain_type:event $1_channel;
+	allow $1_building $1 : domain transition;
+')
+
+define(`create_domain_common', `
 	allow $1 $2:domain { create max_vcpus setdomainmaxmem setaddrsize
-			getdomaininfo hypercall setvcpucontext scheduler
-			unpause getvcpuinfo getvcpuextstate getaddrsize
-			getvcpuaffinity };
+			getdomaininfo hypercall setvcpucontext setextvcpucontext
+			scheduler getvcpuinfo getvcpuextstate getaddrsize
+			getvcpuaffinity setvcpuaffinity };
 	allow $1 $2:security check_context;
 	allow $1 $2:shadow enable;
 	allow $1 $2:mmu {map_read map_write adjust memorymap physmap pinpage};
 	allow $1 $2:grant setup;
-	allow $1 $2:hvm { cacheattr getparam hvmctl irqlevel pciroute setparam pcilevel trackdirtyvram };
-	allow $1 $2_$1_channel:event create;
+	allow $1 $2:hvm { cacheattr getparam hvmctl irqlevel pciroute sethvmc setparam pcilevel trackdirtyvram };
+')
+
+# create_domain(priv, target)
+#   Allow a domain to be created directly
+define(`create_domain', `
+	create_domain_common($1, $2)
+	allow $1 $2_channel:event create;
+')
+
+# create_domain_build_label(priv, target)
+#   Allow a domain to be created via its domain build label
+define(`create_domain_build_label', `
+	create_domain_common($1, $2_building)
+	allow $1 $2_channel:event create;
+	allow $1 $2_building:domain2 relabelfrom;
+	allow $1 $2:domain2 relabelto;
 ')
 
 # manage_domain(priv, target)
@@ -37,6 +60,15 @@ define(`manage_domain', `
 			setvcpuaffinity setdomainmaxmem };
 ')
 
+# migrate_domain_out(priv, target)
+#   Allow creation of a snapshot or migration image from a domain
+#   (inbound migration is the same as domain creation)
+define(`migrate_domain_out', `
+	allow $1 $2:hvm { gethvmc getparam irqlevel };
+	allow $1 $2:mmu { stat pageinfo map_read };
+	allow $1 $2:domain { getaddrsize getvcpucontext getextvcpucontext getvcpuextstate pause destroy };
+')
+
 ################################################################################
 #
 # Inter-domain communication
@@ -47,8 +79,6 @@ define(`manage_domain', `
 #   This allows an event channel to be created from domains with labels
 #   <source> to <dest> and will label it <chan-label>
 define(`create_channel', `
-	type $3, event_type;
-	type_transition $1 $2:event $3;
 	allow $1 $3:event { create send status };
 	allow $3 $2:event { bind };
 ')
@@ -56,8 +86,8 @@ define(`create_channel', `
 # domain_event_comms(dom1, dom2)
 #   Allow two domain types to communicate using event channels
 define(`domain_event_comms', `
-	create_channel($1, $2, $1_$2_channel)
-	create_channel($2, $1, $2_$1_channel)
+	create_channel($1, $2, $1_channel)
+	create_channel($2, $1, $2_channel)
 ')
 
 # domain_comms(dom1, dom2)
@@ -72,7 +102,7 @@ define(`domain_comms', `
 #   Allow a domain types to communicate with others of its type using grants
 #   and event channels (this includes event channels to DOMID_SELF)
 define(`domain_self_comms', `
-	create_channel($1, $1, $1_self_channel)
+	create_channel($1, $1, $1_channel)
 	allow $1 $1:grant { map_read map_write copy unmap };
 ')
 
diff --git a/tools/flask/policy/policy/modules/xen/xen.te b/tools/flask/policy/policy/modules/xen/xen.te
index 9550397f8e..116215384b 100644
--- a/tools/flask/policy/policy/modules/xen/xen.te
+++ b/tools/flask/policy/policy/modules/xen/xen.te
@@ -90,6 +90,7 @@ create_domain(dom0_t, isolated_domU_t)
 manage_domain(dom0_t, isolated_domU_t)
 domain_comms(dom0_t, isolated_domU_t)
 
+# Declare a boolean that denies creation of prot_domU_t domains
 gen_bool(prot_doms_locked, false)
 declare_domain(prot_domU_t)
 if (!prot_doms_locked) {
@@ -111,6 +112,15 @@ manage_domain(dom0_t, dm_dom_t)
 domain_comms(dom0_t, dm_dom_t)
 device_model(dm_dom_t, domHVM_t)
 
+# nomigrate_t must be built via the nomigrate_t_building label; once built,
+# dom0 cannot read its memory.
+declare_domain(nomigrate_t)
+declare_build_label(nomigrate_t)
+create_domain_build_label(dom0_t, nomigrate_t)
+manage_domain(dom0_t, nomigrate_t)
+domain_comms(dom0_t, nomigrate_t)
+domain_self_comms(nomigrate_t)
+
 ###############################################################################
 #
 # Device delegation