1. Secure Operating Systems Lesson 2: OS Fundamentals

2. Security • Very informally, protecting us for Bad Things™ • More formally: • Confidentiality • Integrity • Availability • It is VERY hard for an application to be secure if the OS it is running on doesn’t help this

3. What OS Do • Four levels: • Hardware • OS • Applications • Users • OS is the program most intimately involved with the hardware • Borders of the OS hard to define… Minesweeper?

4. Computer Systems Organization • Parts: • CPU • Main memory • IO (disk controller) • USB • Graphics adapter • Connected by a bus (or two…) • The OS helps all this work together

5. Computer Systems Architecture • Lots of different architectures • Von Neumann • Single Process • Multiprocessor • Symmetric/asymmetric multiprocessing • Multicore • Clustered systems

7. OS Structure • Multiprogramming • Doing more than one thing • Helps drive up CPU utilization • Time sharing/multitasking • Processes, and threads, and… • Swapping, virtual memory

8. Operating System Operations • Most modern OS are interrupt drive • A trap or exception drives control from the user process to the OS • This leads to “dual mode operation” • Must be able to tell the difference between user code and the OS code • Implemented with a “mode bit” • Often called User mode and Kernel mode

9. Privilege • The OS wants to be sure it can always regain control • Need a timer – has to have hardware force the control change • Some instructions should also only be callable from kernel (system) mode • Example: timer management

10. Process Management • OS needs to schedule processes and threads • Create and delete processes • Suspend and resume processes • Ideally, allow for process synchronizationand process communication • These can get iffy with respect to security

11. Memory Management • Managing physical memory is a nightmare • Is memory executable? • Virtual addresses v. Physical • OS must track who is using what • Often the implementation depends on the hardware support

12. Protection and Security • Protection: any mechanism that controls access to something (typically, a resource) • Security: slightly more subtle. Things can be technically working, but still insecure (think: lost password) • Will consider UIDs a lot, and permissions… also capabilities

13. Special Purpose Systems • Real time systems • Handhelds • Distributed

14. Open and Closed Source • Different design methodologies • Classically, Windows versus Linux – lots of tradeoffs here, you could do a whole class on it

15. Assignment • Make sure you can access the SVN • Read Chapter 1 of OSC • Make sure you have a Gentoo Linux VM and a Windows XP 32-bit VM up and running (unless you want to experiment on live machines)

16. Questions & Comments • What do you want to know?