efi_loader: check map_key in ExitBootServices

The UEFI spec requires that the memory map key is checked in
ExitBootServices().

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index 86cb9ba..6bd64b9 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -1854,6 +1854,10 @@
 
 	EFI_ENTRY("%p, %ld", image_handle, map_key);
 
+	/* Check that the caller has read the current memory map */
+	if (map_key != efi_memory_map_key)
+		return EFI_INVALID_PARAMETER;
+
 	/* Make sure that notification functions are not called anymore */
 	efi_tpl = TPL_HIGH_LEVEL;