Cloud environments are being increasingly used for deploying and executing business processes to provide a high level of performance with low operating cost. Nevertheless, due to the lack of explicit and formal description of the resource perspective in existing business processes, cloud resources cannot be efficiently and optimally managed. The aim of the present paper is to offer a formal definition of the resource perspective in business processes as a step towards ensuring correct and optimal Cloud resource allocation in business process modeling. Concretely, we propose a formalism based on the Event-B for specifying Cloud resource allocation policies in business process models. This formal specification is used to formally validate the consistency of Cloud resource allocation for process modeling at design time, and to analyze and check its correctness according to users needs and resource properties. In order to show its feasibility, our approach has been tested using a real use case study from an industrial partner