efi_loader: UEFI variable persistence

Persist non-volatile UEFI variables in a file on the EFI system partition.

The file is written whenever a non-volatile UEFI variable is changed after
initialization of the UEFI sub-system.

The file is read during the UEFI sub-system initialization to restore
non-volatile UEFI variables.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_variable.c

@@ -988,6 +988,11 @@ out:
 			ret = EFI_SUCCESS;
 	}
 
+	/* Write non-volatile EFI variables to file */
+	if (attributes & EFI_VARIABLE_NON_VOLATILE &&
+	    ret == EFI_SUCCESS && efi_obj_list_initialized == EFI_SUCCESS)
+		efi_var_to_file();
+
 err:
 	free(native_name);
 	free(old_data);
@@ -1083,6 +1088,7 @@ efi_set_variable_runtime(u16 *variable_name, const efi_guid_t *vendor,
  */
 void efi_variables_boot_exit_notify(void)
 {
+	/* Switch variable services functions to runtime version */
 	efi_runtime_services.get_variable = efi_get_variable_runtime;
 	efi_runtime_services.get_next_variable_name =
 				efi_get_next_variable_name_runtime;
@@ -1102,6 +1108,8 @@ efi_status_t efi_init_variables(void)
 	efi_status_t ret;
 
 	ret = efi_init_secure_state();
+	if (ret != EFI_SUCCESS)
+		return ret;
 
-	return ret;
+	return efi_var_from_file();
 }