project-lakitu: Set file permissions of /boot/efi/boot/grub.cfg to 400

BUG=b/177854826
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I0cd6683684602abbbf2174e12181a6051fbb8dd4
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/11774
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Roy Yang <royyang@google.com>
diff --git a/project-lakitu/scripts/board_specific_setup.sh b/project-lakitu/scripts/board_specific_setup.sh
index 2e56ce3..fe38827 100644
--- a/project-lakitu/scripts/board_specific_setup.sh
+++ b/project-lakitu/scripts/board_specific_setup.sh
@@ -243,6 +243,9 @@
     "${root_fs_dir}"/lib/systemd/system \
     -type f -name *.timer | xargs sudo chmod go-wrx
 
+  # Set grub.cfg file permissions to 400 as recommended by CIS
+  sudo chmod 400 "${root_fs_dir}"/boot/efi/boot/grub.cfg
+
   local shim_arch=""
   if [[ "${ARCH}" == "amd64" ]]; then
     shim_arch="x64"