The present invention concerns a method of protecting sensitive data, and a corresponding computing system processing device, comprising: entering, by a processing device, a sensitive date access mode in-which sensitive data is accessible; restricting, by a program running in the sensitive data access mode, one or more accessible address ranges for a non-secure function, and calling, from the sensitive data access mode, the non-secure function; and entering, by the processing device, a further operating mode to execute the non-secure function during which the processing device has access to only the one or more accessible address ranges.