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>

3 files changed, 24 insertions, 1 deletions

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 9d20086347..b183255568 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -1182,6 +1182,10 @@ static void domcreate_complete(libxl__egc *egc,
                                int rc)
 {
     STATE_AO_GC(dcs->ao);
+    libxl_domain_config *const d_config = dcs->guest_config;
+
+    if (!rc && d_config->b_info.exec_ssidref)
+        rc = xc_flask_relabel_domain(CTX->xch, dcs->guest_domid, d_config->b_info.exec_ssidref);
 
     if (rc) {
         if (dcs->guest_domid) {
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 7eac4a8709..93524f0645 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -268,6 +268,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
     ("video_memkb",     MemKB),
     ("shadow_memkb",    MemKB),
     ("rtc_timeoffset",  uint32),
+    ("exec_ssidref",    uint32),
     ("localtime",       libxl_defbool),
     ("disable_migrate", libxl_defbool),
     ("cpuid",           libxl_cpuid_policy_list),
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 4b75fc3d66..e964bf1728 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -596,16 +596,34 @@ static void parse_config_data(const char *config_source,
         exit(1);
     }
 
-    if (!xlu_cfg_get_string (config, "seclabel", &buf, 0)) {
+    if (!xlu_cfg_get_string (config, "init_seclabel", &buf, 0)) {
         e = libxl_flask_context_to_sid(ctx, (char *)buf, strlen(buf),
                                     &c_info->ssidref);
         if (e) {
             if (errno == ENOSYS) {
+                fprintf(stderr, "XSM Disabled: init_seclabel not supported\n");
+            } else {
+                fprintf(stderr, "Invalid init_seclabel: %s\n", buf);
+                exit(1);
+            }
+        }
+    }
+
+    if (!xlu_cfg_get_string (config, "seclabel", &buf, 0)) {
+        uint32_t ssidref;
+        e = libxl_flask_context_to_sid(ctx, (char *)buf, strlen(buf),
+                                    &ssidref);
+        if (e) {
+            if (errno == ENOSYS) {
                 fprintf(stderr, "XSM Disabled: seclabel not supported\n");
             } else {
                 fprintf(stderr, "Invalid seclabel: %s\n", buf);
                 exit(1);
             }
+        } else if (c_info->ssidref) {
+            b_info->exec_ssidref = ssidref;
+        } else {
+            c_info->ssidref = ssidref;
         }
     }