Host and Application Security Lesson 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… UserApplication 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?