Any modern computer system must provide the means for the operating system to control access to the
memory system. A user process should not be allowed to modify its read-only text section. Nor should it be
allowed to read or modify any of the code and data structures in the kernel. It should not be allowed to read
or write the private memory of other processes, and it should not be allowed to modify any virtual pages
that are shared with other processes, unless all parties explicitly allow it (via calls to explicit interprocess
communication system calls).