Operating Systems (CS 161) – Spring 2021

Module Topic: Ethical Tradeoffs in Operating Systems Design: A Look at Cost-Benefit Analysis
Module Author: Elís Miller Larsen

Course Level: Upper Level Undergraduate
AY: 2020-2021

Course Description: “This is an in-depth course in operating systems design and implementation, focusing on multicore operating systems kernels. Operating systems are some of the most complex software artifacts that exist. Kernels abstract the features provided by computer hardware, making those features safer and more convenient to use. This means that OS designers have to understand how hardware works (at least at the level of specifications) and how software works. OS programmers also must become comfortable with navigating in, and contributing to, code bases too large to wholly understand. Most of us can pick up this important skill.

The course uses Chickadee, an operating system based on CS 61 WeensyOS. Chickadee takes advantage of newer hardware, language, and OS design features than many teaching operating systems.” (Course description)

Semesters Taught: Spring 2019, Spring 2020, Spring 2021, Spring 2022

Tags

• operating systems (CS)
• system security (CS)
• security vulnerabilities (CS)
• patches (CS)
• stakeholders (CS)
• cost- benefit analysis (CBA) (phil)
• normative statements (phil)
• rights (phil)

Module Overview

System design often involves tradeoffs, e.g. increasing speed at the cost of at the cost of security or improving features at the cost of privacy. In this module we discuss the ethical considerations present in these tradeoffs. In order to assess what to do in situations where tradeoffs arise, students are introduced to the cost-benefit analysis framework.

Cost-benefit analysis (CBA) is a systematic approach for measuring the strengths and weaknesses of the available options. Options are compared in order to provide a “best approach” recommendation. In business and economics, CBA is viewed as a recommendation model only. In ethics, CBA is viewed as a normative model—a model that tells us what we should do. Students are asked to apply this model to specific scenarios in system design in order to assess what is the most responsible design choice

    Connection to Course Technical Material

One of the major focuses of the course is on system security, including identifying and shoring up system vulnerabilities. Decisions regarding whether or not to make a system more secure typically involves consideration of costs to the company such as time or money. However, this module introduces the idea that there are also ethical costs involved in system security that designers should be cognizant of.

Goals

Module Goals

By the end of the module, students will be able to:

1. Introduce a case study that illustrates how there are ethical tradeoffs in system design
2. Identify what those tradeoffs are
3. Break down the 6 steps of CBA from the reading assignment so that students are clear about how to apply CBA as a model for what we should do
4. Review limitations of CBA as a framework of ethical analysis
5. Have students apply CBA to specific scenarios

    Key Philosophical Questions

Materials

    Key Philosophical Concepts

    Assigned Readings

• Boardman (2006), “Cost-Benefit Analysis: Concepts and Practice, excerpts.”
• Heinzerling & Ackerman (2002), “Pricing the Priceless: Cost-Benefit Analysis of Environmental Protection”

Implementation

Class Agenda

1. Introduce “Snooping Attack” case study in order to illustrate the ethical tradeoff when applying a patch.
2. Review CBA steps from reading
3. Class Activity: have students apply CBA to a specific (hypothetical) scenario
4. Debrief. Review student responses and discuss the limitations of CBA students encountered.

    Sample Class Activity

Hypothetical Scenario: Imagine that you work at a start-up company that makes an operating system called Sparrow. Sparrow targets desktop and laptop machines and uses virtualization technology to run applications made for both Windows and MacOS. As you test Sparrow in preparation for its initial release, you discover two bugs.

1. The first bug is triggered when a user configures Sparrow to use a non-English keyboard setup (e.g., Japanese or Arabic). Such users have a 3% higher risk of their file data being corrupted by Sparrow’s file system (which has subtle errors in the way that it handles filenames that don’t use English characters).
2. The second bug involves the way that Sparrow implements virtualization. When Sparrow simultaneously runs a VM for a MacOS app at the same time that a VM for a Windows app runs, there is a 3% chance that the Windows app will not be properly isolated; if this happens, then the Windows app (if malicious) can tamper with the state of the MacOS app.

If Sparrow is not released by its target date, the venture capitalists who fund your company may get upset and may refuse to provide subsequent funding.

What do you do? Use CBA to determine how your company should respond to the discovery of these two bugs.

Conduct a cost benefit analysis. Students are provided a table in order to fill out and assess the costs, benefits, and stakeholders involved.

    Module Assignment

Students are assessed on CBA knowledge for the final exam.

Lessons Learned

Originally this module had the Class Activity at the end of the session. The TA learned that more time is required for the activity. In addition, having the activity in the middle of the session would allow the students to discover the limitations of CBA for themselves, rather than have the limitations and criticisms presented to them via lecture.

Through the activity students learn how to (1) apply CBA and (2) recognize limitations for ethical analysis. Some students found that even after applying CBA it wasn’t clear what to do. This discovery by the students is an excellent opportunity for the TA to encourage the use of CBA as a first step and stress the difficulty of ethical problems. This should not be a discouraging discovery, but instead a way for students to recognize the seriousness of the kinds of problems they might encounter as CS professionals.