Chapter 13, Protection Video Solutions, Operating System Concepts Essentials

Problem 1

What are the main differences between capability lists and access lists?

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Problem 2

A Burroughs B7000/B6000 MCP file can be tagged as sensitive data. When such a file is deleted, its storage area is overwritten by some random bits. For what purpose would such a scheme be useful?

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In a ring-protection system, level 0 has the greatest access to objects, and level $n$ (where $n>0$ ) has fewer access rights. The access rights of a program at a particular level in the ring structure are considered a set of capabilities. What is the relationship between the capabilities of a domain at level $j$ and a domain at level $i$ to an object (for $j>i$ )?

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01:14

Problem 4

The RC 4000 system, among others, has defined a tree of processes (called a process tree) such that all the descendants of a process can be given resources (objects) and access rights by their ancestors only. Thus, a descendant can never have the ability to do anything that its ancestors cannot do. The root of the tree is the operating system, which has the ability to do anything. Assume the set of access rights is represented by an access matrix, $A . A(x, y)$ defines the access rights of process $x$ to object $y$. If $x$ is a descendant of $z$, what is the relationship between $A(x, y)$ and $A(z, y)$ for an arbitrary object $y$ ?

Ashley Volpe

Numerade Educator

Problem 5

What protection problems may arise if a shared stack is used for parameter passing?

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02:11

Problem 6

Consider a computing environment where a unique number is associated with each process and each object in the system. Suppose that we allow a process with number $n$ to access an object with number $m$ only if $n>m$. What type of protection structure do we have?

James Kiss

Numerade Educator

Problem 7

Consider a computing environment where a process is given the privilege of accessing an object only $n$ times. Suggest a scheme for implementing this policy.

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Problem 8

If all the access rights to an object are deleted, the object can no longer be accessed. At this point, the object should also be deleted, and the space it occupies should be returned to the system. Suggest an efficient implementation of this scheme.

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Problem 9

Why is it difficult to protect a system in which users are allowed to do their own I/O?

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Problem 10

Capability lists are usually kept within the address space of the user. How does the system ensure that the user cannot modify the contents of the list?

Emily Himsel

Numerade Educator

02:33

Problem 11

Consider the ring-protection scheme in MULTICS. If we were to implement the system calls of a typical operating system and store them in a segment associated with ring 0 , what should be the values stored in the ring field of the segment descriptor? What happens during a system call when a process executing in a higher-numbered ring invokes a procedure in ring 0 ?

Shelby Mohamed

Numerade Educator

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Problem 12

The access-control matrix can be used to determine whether a process can switch from, say, domain A to domain B and enjoy the access privileges of domain $B$. Is this approach equivalent to including the access privileges of domain $\mathrm{B}$ in those of domain $\mathrm{A}$ ?

Victor Salazar

Numerade Educator

06:33

Problem 13

Consider a computer system in which computer games can be played by students only between 10 P.M. and 6 A.M., by faculty members between 5 P.M. and 8 A.M., and by the computer center staff at all times. Suggest a scheme for implementing this policy efficiently.