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>

1 files changed, 4 insertions, 0 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) {