Security in Computing 5th Edition by Shari Lawrence Pfleeger, Charles P Pfleeger, Jonathan Margulies

Exercise 18

Explain why asynchronous I/O activity is a problem with many memory protection schemes, including base/bounds and paging. Suggest a solution to the problem.

Step 1 of 2

Asynchronous I/O with base/bound and paging

The fence register provides the ability to relocate. To separate two user areas, a start address called the base address is being provided. All programs in the specific user area are offset from the base address. A user using the address space may exceed to beyond its limit, so an upper bound is also important to restrict the user from entering into another user area. The upper bound register is called bound register. Thus, to provide separation and maintain the integrity of data the base/bound register scheme is important to be implemented. A pair of base/bound register provides the lower and upper limits of the area specific to that user, so the pair can protect a single user area from other users.

Paging divides the program into equal-sized pieces, pages, and the memory is divided into page frames. With this, the page table name and the related memory address are stored in a page table. Using the page and the offset value, different addresses can be accessed.