Difference between revisions of "Operating Systems 2015F Lecture 22"

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==Video==
==Video==


The video for the lecture given on November 25, 2015 [http://homeostasis.scs.carleton.ca/~soma/os-2015f/lectures/comp3000-2015f-lec21-25Nov2015.mp4 is now available].
The video for the lecture given on November 27, 2015 [http://homeostasis.scs.carleton.ca/~soma/os-2015f/lectures/comp3000-2015f-lec22-27Nov2015.mp4 is now available].


==Notes==
==Notes==


<pre>
<pre>
Lecture 21
Lecture 22
----------
----------


no last assignment
Project
- you need to pass the oral to get credit for it
- Due December 4th by midnight, late penalty is 20%/day


What is research?
Patching
* Asking questions and figuring out the answers
* Questions are much more important than answers
* Questions are much *harder* than answers


What question you ask determines what answer you'll get
Malware detection & operating systems


The research literature
* Most Linux systems don't run "antivirus"
- many many publications
* Most Macs don't run antivirus
- hard to tell what is any good
* iOS devices don't
* some Android devices do


Reseachers know who to trust in their area, and, how in general to determine trust
What does this tell us about those operating systems?
  - do spot checks for obvious errors, based on what you do know
  - not that much
  - do they give full details about what they did? could you reproduce it?
  - it is more about what exists today rather than what could exist
- surprising results require extraordinary evidence


Ideally your OS should only allow you to run "good" code.
Antivirus is what you get when you are likely to run "bad" code.


If you're outside the field, look at
How do operating systems keep out bad code?
  - publication reputation
  * user authentication (accounts and passwords)
  - citation counts and quality
  * otherwise, mostly isolation
  * user permissions (not all users can access all
    resources)
    ("users" are now often applications)
  * firewalls (isolate network connections to apps)
  * supervisor versus user mode on the CPU
    (kernel vs userspace)
  * memory protection (virtual memory)
  * CPU & I/O scheduling to prevent programs from
    monopolizing resources


to learn more about operating systems research...
* Desktop OSs assume installed applications can be trusted
what are the well-respected venues?
  - they are allowed to do arbitrary damage


Conferences, not journals
* Mobile OSs do not trust most applications, or greatly limit trust


  USENIX OSDI
Android
  ACM SOSP
- applications can be trusted in different ways
  - user can decide what apps are trustworthy for different
  things
  - users will look at an app's permissions and decide
    whether it is worthy of the trust level requested
  - regular users are not sufficiently knowledgeable to make such trust decision


When should you *really* look at the research literature?
- every app runs as a different user.  Each app can only access its own files
- but, then we have processes that accept requests from apps to access just about anything else


You're trying to solve a hard problem and aren't sure what approach to take.
* iOS sandboxing
* look to see what other people have done in response to similar problems!
  - OS-level virtualization: every app gets its own userspace
  - then iOS puts things in that "sandbox" that it deems
    safe to access


What about computer security?
On Android, you've always been able to install keyboards
  * even more publications
On iOS, only recently have keyboards been added
  - and they can't be used for passwords


But there's a truth to research...
on iOS, Apple-supplied apps have always had more access
- most of it isn't any good


Why?
What is antivirus?
  - a lot of research doesn't work in practice
  - downloader's remorse
  - a lot of conclusions are premature
  - or, I really shouldn't have installed that


Computer security research is mostly bad
How does antivirus work?
- tech equivalent to criminal profiling
  - their history
  - their behavior
  - their friends
- profiling is fundamentally hard and limited
- profiling is especially hard because of lies


Cryptography is mostly bad. And dangerous.
How do you catch the lies of programs?
* easy to implement
  - surveillance
* hard to implement well


If you make a mistake, your crypto is worse than useless
all antivirus need kernel-level help to work
* security cannot be specified or completely defined
why can't malware have kernel-level help?
* attacks exploit details that you didn't think about
  - that's a kernel-level rootkit


Timing attacks
Nexus (border control) for operating systems is...
- code signing


Game in encryption: encrypt and decrypt without disclosing the plaintext or the key
Code signing in any sort of "open context" is suspect


For many encryption algorithms, execution time is a function of the plaintext and/or key
App store signing is not bad


Watch how long a computer takes to encrypt something, and you can figure out the key
Traditional OSs are for running "trusted" code


1970's, Data Encryption Standard (DES)
We have the technology for running untrusted code.
- first developed by IBM
It is called a web browser.
- "fixed" by the NSA
  - halved the key (much easier to break)
  - fiddled with the constants in the algorithm
 
Any security technology may improve and reduce your security at the same time
 
security is confidentiality, availability, and integrity
Example: encrypting a hard disk
 
Why not use biometrics
- fingerprints
- facial recognition
 
It is all about your threat model
- any technology helps with certain risks and harms versus others
- what do you care about?
 
Tradeoffs are inherent to technology
</pre>
</pre>

Latest revision as of 16:42, 27 November 2015

Video

The video for the lecture given on November 27, 2015 is now available.

Notes

Lecture 22
----------

Project
 - you need to pass the oral to get credit for it
 - Due December 4th by midnight, late penalty is 20%/day

Patching

Malware detection & operating systems

* Most Linux systems don't run "antivirus"
* Most Macs don't run antivirus
* iOS devices don't
* some Android devices do

What does this tell us about those operating systems?
 - not that much
 - it is more about what exists today rather than what could exist

Ideally your OS should only allow you to run "good" code.
Antivirus is what you get when you are likely to run "bad" code.

How do operating systems keep out bad code?
 * user authentication (accounts and passwords)
 * otherwise, mostly isolation
   * user permissions (not all users can access all
     resources)
     ("users" are now often applications)
   * firewalls (isolate network connections to apps)
   * supervisor versus user mode on the CPU
     (kernel vs userspace)
   * memory protection (virtual memory)
   * CPU & I/O scheduling to prevent programs from
     monopolizing resources

* Desktop OSs assume installed applications can be trusted
  - they are allowed to do arbitrary damage

* Mobile OSs do not trust most applications, or greatly limit trust

Android
 - applications can be trusted in different ways
 - user can decide what apps are trustworthy for different
   things
   - users will look at an app's permissions and decide
     whether it is worthy of the trust level requested
 - regular users are not sufficiently knowledgeable to make such trust decision

 - every app runs as a different user.  Each app can only access its own files
 - but, then we have processes that accept requests from apps to access just about anything else
 

* iOS sandboxing
  - OS-level virtualization: every app gets its own userspace
  - then iOS puts things in that "sandbox" that it deems
    safe to access

On Android, you've always been able to install keyboards
On iOS, only recently have keyboards been added
 - and they can't be used for passwords

on iOS, Apple-supplied apps have always had more access

What is antivirus?
 - downloader's remorse
 - or, I really shouldn't have installed that

How does antivirus work?
 - tech equivalent to criminal profiling
   - their history
   - their behavior
   - their friends
 - profiling is fundamentally hard and limited
 - profiling is especially hard because of lies

How do you catch the lies of programs?
 - surveillance

all antivirus need kernel-level help to work
why can't malware have kernel-level help?
  - that's a kernel-level rootkit

Nexus (border control) for operating systems is...
 - code signing

Code signing in any sort of "open context" is suspect

App store signing is not bad

Traditional OSs are for running "trusted" code

We have the technology for running untrusted code.
It is called a web browser.
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