efi_loader: don't load signature database from file

The UEFI specification requires that the signature database may only be
stored in tamper-resistant storage. So these variable may not be read
from an unsigned file.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/include/efi_variable.h b/include/efi_variable.h
index 4623a64..2d97655 100644
--- a/include/efi_variable.h
+++ b/include/efi_variable.h
@@ -161,10 +161,13 @@
 /**
  * efi_var_restore() - restore EFI variables from buffer
  *
+ * Only if @safe is set secure boot related variables will be restored.
+ *
  * @buf:	buffer
+ * @safe:	restoring from tamper-resistant storage
  * Return:	status code
  */
-efi_status_t efi_var_restore(struct efi_var_file *buf);
+efi_status_t efi_var_restore(struct efi_var_file *buf, bool safe);
 
 /**
  * efi_var_from_file() - read variables from file