Method of protecting programs and data in a computer against unauthorized access and modification by monitoring address regions

A method of real-time monitoring of memory regions in a data processing device having a plurality of bus lines and having a memory with a plurality of memory locations, with each memory region including a plurality of memory locations, said method comprising the steps of:

• associating selected memory regions of the memory with different access levels, an access level associated with a memory region indicating whether read operations from that memory region are authorized, whether write operations to that memory region are authorized, and whether program running operations from that memory region are authorized;
• storing the associations of memory regions and access levels;
• comparing a level of an attempted access and a memory region to which the attempted access is directed with the stored associations, the comparing step comprising the step of checking signals on at least some of the bus lines;
• and
• detecting if the level of the attempted access and the memory region are not among the stored associations, thereby to detect an unauthorized attempted access;
• and,
• wherein said step of associating includes the steps of:
• associating a first region of the memory with a zeroth level of access defined by prohibiting reading out of and writing into predetermined memory locations of the first region and permitting programs to be started only from certain memory locations in the first region;
• associating a second region of the memory with a first level of access defined by prohibiting reading out of and writing into predetermined memory locations of the second region and permitting programs to be run from all memory locations in the second region;
• associating a third region of the memory with a second level of access defined by permitting reading out of memory locations of only certain portions of the third region and prohibiting programs from being run from all memory locations in the third region;
• associating a fourth region of the memory with a third level of access defined by permitting reading out of and reading into memory locations of only certain portions of the fourth region and prohibiting programs from being run from all memory locations in the fourth region;
• associating a fifth region of the memory with a fourth level of access defined by permitting reading out of memory locations of only certain portions of the fifth region and permitting programs to be run from all memory locations in the fifth region;
• associating a sixth region of the memory with a fifth level of access defined by permitting reading out of and reading into memory locations of only certain portions of the sixth region and permitting programs to be run from all memory locations in the sixth region;
• and
• associating a seventh region of the memory with a sixth level of access defined by permitting reading out of and reading into all memory locations of the seventh region.