1. Accounting, Protection, Security and More Fault Handling Gotchas May 26, 2000 Instructor: Gary Kimura

2. 26/27/2015 Today’s Topics Accounting Protection and security Handling faults

3. 36/27/2015 Accounting Systems In large old computing centers accounting systems were very common. –Not that applicable in a PC environment. –But again useful in a network The task was not necessarily to restrict usage but to hold individual users accountable for their usage of the system Why? –Charge back to make money –Monitor system usage monitoring –When to buy a bigger system –Locate usage hogs

4. 46/27/2015 Things to measure We measure things that give us a metric for overall and specific system usage –CPU Usage –Main Memory Usage –Disk Usage –Paper Usage –Connect time usage How to do the measurement is mostly pretty obvious but not always…

5. 56/27/2015 Quotas A means of limiting resource usage by an individual or a group Typical quota items include –Disk usage –Memory usage –Open handle usage –Mail box usage Either the system prohibits a user’s usage from exceeding their quota or sounds a lot of bells and whistles when they do

6. 66/27/2015 Protection and Security “Don’t trust anyone” –Naïve user with dumb mistakes –Destructive malicious user DOD security levels (A – D) –D: least protected system (MS-DOS pass any tests) –C: discretionary protection and accountability with two subgroups (C1 and C2) –B: mandatory protection (security levels) –A: highest level of security

7. 76/27/2015 Protection put on objects and users –Access control lists –Identify either a group or a individual user –Indicates if access is allowed or denied –Object reuse –Be sure to clear out memory and secondary storage before reusing objects space –Revocation –Each user/process has an ID and usually a list of access rights –Some systems allow the system to revoke the access rights to an existing process, some systems do not

8. 86/27/2015 More security issues –Authentication –Password, etc –Program threats –Trojan Horses –Trap doors –System threats –Worms –Viruses –Encryption –Denial of service attacks

9. 96/27/2015 Places where page faults occur User invoked faults –Code –Data –Both Kernel invoked faults –Code –Data –Both

10. 106/27/2015 Double faults In some systems it is okay for a page fault handler to itself cause a fault There is somewhat a chicken and egg problem that needs to be addressed Eventually the last fault needs all of its data code to be resident in memory It is possible to pin down your code and data, however doing so usually takes more CPU cycles than it’s worth. So just make the code nonpaged to start with.

11. 116/27/2015 Collided page faults When two processes both fault in the same page at the same time we can come up with a collided page fault. The same can happen if one process touches a page while the fault is almost through being handled

12. 126/27/2015 Things to come Distributed Systems RPC Review Final exam day