Host and Application SecurityLesson 5: The Role of an OS

Environment What is the output of a program?

Right… it’s all about the Environment What is an operating system? How did Oses come about? Some examples and the security implications

of them

Historically Batched systems Multiprogrammed Systems Time sharing Real-time systems

Services Provided Essentially, a “resource allocator”

CPU time Memory space File storage space IO…

Provides abstraction What’s in there?

Everything the vendor ships “the one program running at all times on the computer”

(Silberschatz)

Pictorially…

User Application Operating System Hardware

OS Architecture Monolothic

Things are loaded into the operating system, and run with the privileges of the OS

Example: Linux Microkernel

Take everything that you don’t need out and put it user mode Example: Symbian

“Hybrid” Kernel Some blending of the above Example: Windows

Windows 7 DOS: One program ruled all Windows 3.1: Some kind of multitasking Windows NT: A protected environment Windows 95, 98, ME: Better separation, better

multitasking, still based on DOS Windows 2000: Based on NT 4 codebase Windows XP: Possibly “most successful” Windows OS Windows Vista: Added UAC, amongst other things Windows 7: Lots of security enhancements

Unix

Source: Wikipedia

Questions?