PA2 - CS 4414 Operating Systems Fall 2009 Assignment#2 Due...

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1 CS 4414: Operating Systems Fall 2009 Assignment #2 Due T uesday Thursday Sept 24, 11am Part 1. (worth 25%) . Short Answer (Answer all 8 questions). 1. In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems. a. What are two such problems? b. Can we ensure the same degree of security in a time-shared machine as we have in a dedicated machine? Explain your answer. 2. We have stressed the need for an operating system to make efficient use of the computing hardware. When is it appropriate for the operating system to forsake this principle and to “waste” resources? Why is such a system not really wasteful? 3. Which of the following instructions should be privileged? a. Set value of timer. b. Read the clock. c. Clear memory. d. Turn off interrupts. e. Switch from user to monitor mode. 4. Give two reasons why caches are useful. What problems do they solve? What problems do they cause? If a cache can be made as large as the device for which it is caching (for instance, a cache as large as a disk), why not make it that large and eliminate the device? 5. Give one reason why a closed-source proprietary operating system like Windows should have a better quality than an open-source operating system like Linux. Now give one reason why an open-source operating system like Linux should have better quality than a closed-source operating system like Windows. 6. What do abstraction and virtualization have in common? How are they different? Give an example of each. 7. Evaluate monolithic, layered and microkernel architectures according to: a. Efficiency b. Robustness. c. Extensibility. d. Security. 8. Processor speeds have doubled roughly every 18 months. Has overall computer performance doubled at the same rate? Why or why not? Part 2. Programming Assignment (System Calls) – worth 75% Operating Systems have utilities to show a snapshot of currently-running processes -- e.g., UNIX/Linux has ps and top , while Windows has the Windows Task Manager (via ctrl-alt-del) and third-party tools.
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2 System administrators sometimes use these tools to monitor legitimate system performance as well as look for strange processes that might originate from system intrusions. Clearly, computer hackers often try to hide their processes from the prying eyes of system administrators. In this programming assignment, we’ll write system calls that make the process disappear from the Windows Task Manager and then re- appear (!). While this specific approach is unlikely to be used in a real attack, understanding how this can be done can help you in general better understand how to beat computer attackers, as well as provide a better understanding of operating systems. You are strongly encouraged to do this assignment in a team of two people collaboratively. You can do this assignment by yourself, and no team can have more than two people. Please read the entire assignment first so that you understand the “big picture”. There are five
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This note was uploaded on 09/25/2009 for the course CS 4124 taught by Professor Marty during the Spring '09 term at UVA.

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PA2 - CS 4414 Operating Systems Fall 2009 Assignment#2 Due...

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