Abstract: A mandatory secure access control model named SOSACM of Operating System that is based on the multi-level security policy is put forward. Its confidetiality inherits the BLP model, and its definition of integrity is on the basis of Biba model. But in fact, the simple conjunct of BLP and Biba models will make some legal object not accessible because the directions of information flow in the BLP model and integrity in the Biba model are opposite. In the model, a trusted level strategy that makes the combination of confidentiality and integrity property tight has been developed, which should ensure that subjects can access objects legally. The model will be beneficial to its application to constructing secure Operating Systems in future.

Key words: multi-level security strategy, mandatory access control, security model, operating system