20_linux_xen: Support Xen Security Modules (XSM/FLASK)

XSM is enabled by adding "flask=enforcing" as a Xen command line
argument, and providing the policy file as a grub module.

We make entries for both with and without XSM.  If XSM is not compiled
into Xen, then there are no policy files, so no change to the boot
options.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/overlay-buster/etc/grub.d/20_linux_xen b/overlay-buster/etc/grub.d/20_linux_xen
index 01dfcb577d6701ceb51cc0bfdd63b26ef92ccd8a..4d3294a253b34760e36bbd61536654ec0e483260 100755 (executable)
--- a/overlay-buster/etc/grub.d/20_linux_xen
+++ b/overlay-buster/etc/grub.d/20_linux_xen
@@ -84,6 +84,11 @@ esac
 title_correction_code=
 
 linux_entry ()
+{
+  linux_entry_xsm "$@" false
+  linux_entry_xsm "$@" true
+}
+linux_entry_xsm ()
 {
   os="$1"
   version="$2"
@@ -91,6 +96,18 @@ linux_entry ()
   type="$4"
   args="$5"
   xen_args="$6"
+  xsm="$7"
+  # If user wants to enable XSM support, make sure there's
+  # corresponding policy file.
+  if ${xsm} ; then
+      xenpolicy="xenpolicy-$xen_version"
+      if test ! -e "${xen_dirname}/${xenpolicy}" ; then
+         return
+      fi
+      xen_args="$xen_args flask=enforcing"
+      xen_version="$(gettext_printf "%s (XSM enabled)" "$xen_version")"
+      # xen_version is used for messages only; actual file is xen_basename
+  fi
   if [ -z "$boot_device_id" ]; then
       boot_device_id="$(grub_get_device_id "${GRUB_DEVICE}")"
   fi
@@ -140,6 +157,13 @@ EOF
     sed "s/^/$submenu_indentation/" << EOF
        echo    '$(echo "$message" | grub_quote)'
        ${module_loader}        --nounzip   ${rel_dirname}/${initrd}
+EOF
+  fi
+  if test -n "${xenpolicy}" ; then
+    message="$(gettext_printf "Loading XSM policy ...")"
+    sed "s/^/$submenu_indentation/" << EOF
+       echo    '$(echo "$message" | grub_quote)'
+       ${module_loader}     ${rel_dirname}/${xenpolicy}
 EOF
   fi
   sed "s/^/$submenu_indentation/" << EOF