efi_loader: detach runtime in ExitBootServices()

Linux can be called with a command line parameter efi=novamap, cf.
commit 4e46c2a95621 ("efi/arm/arm64: Allow SetVirtualAddressMap() to be
omitted"). In this case SetVirtualAddressMap() is not called after
ExitBootServices().

OpenBSD 32bit does not call SetVirtualAddressMap() either.

Runtime services must be set to an implementation supported at runtime
in ExitBootServices().

Reported-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Suggested-by: Alexander Graf <agraf@csgraf.de>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

include/efi_loader.h

@@ -333,6 +333,8 @@ void efi_variables_boot_exit_notify(void);
 efi_status_t efi_root_node_register(void);
 /* Called by bootefi to initialize runtime */
 efi_status_t efi_initialize_system_table(void);
+/* efi_runtime_detach() - detach unimplemented runtime functions */
+void efi_runtime_detach(void);
 /* Called by bootefi to make console interface available */
 efi_status_t efi_console_register(void);
 /* Called by bootefi to make all disk storage accessible as EFI objects */

lib/efi_loader/efi_boottime.c

@@ -1973,6 +1973,9 @@ static efi_status_t EFIAPI efi_exit_boot_services(efi_handle_t image_handle,
 
 	board_quiesce_devices();
 
+	/* Patch out unsupported runtime function */
+	efi_runtime_detach();
+
 	/* Fix up caches for EFI payloads if necessary */
 	efi_exit_caches();
 

lib/efi_loader/efi_runtime.c

@@ -398,7 +398,7 @@ static bool efi_is_runtime_service_pointer(void *p)
 /**
  * efi_runtime_detach() - detach unimplemented runtime functions
  */
-static __efi_runtime void efi_runtime_detach(void)
+void efi_runtime_detach(void)
 {
 	efi_runtime_services.reset_system = efi_reset_system;
 	efi_runtime_services.get_time = efi_get_time;