Luc: /* Notes */

2018-03-31T05:36:42Z

Notes

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	==Notes==		==Notes==
			Senses of Virtual:
			JVM/CLR
			Hardware virtual machines
			--> Hypervisors
			Virtual Memory
			Virtual Reality
			Virtual Functions
			VFS Layer (Virtual File System)

			What is really meant by virtual in this context?
			-Portability
			-Hardware -> Software (Made into)
			-Level of abstraction
			--Resource Abstraction

			Subject ---> Resource
			^Virtualization breaks this connection, becoming:

			Subject --->Resource
			\|-----> Abstraction \|

			Example:
			File containing digits of pi, is really just a function that generates digits
			From the perspective of the Subject the Abstraction is the resource, it's the same thing as having an actual file

			Why is this a general strategy for security?
			Abstraction is a means of control
			Controlling the abstraction controls what the subject perceives. It's not what is actual there, it's keeping the subject "safe"
			Social control?
			Buy into an abstraction of reality
			Abstraction
			Tool for how people perceive reality
			Civil instutions, money, politics
			Live in the real world, but abstraction within out minds
			Lots of power in abstractions
			Abstraction is a method of control

			Note: By controlling the abstraction we can enforce security properties that would otherwise be very difficult.

			Virtual Memory
			Each program gets it's own memory
			You can escape the box when you can't see the box
			All the memory they see, is their's
			It thinks it has its whole address range
			Enforces memory safety in allocation, but also prevents programs of messing with eachother

			Virtual Functions
			A place you can excicibit control
			Basically a direction table
			But also leads to less to security in the sense that the table can be manipulated


			Hardware Virtual Machines
			OS is running, thinks it's accessing the hardware, but it is accessing the hypervisor. THis allows for "windows in a window", multiple os running
			Unfortunately
			Somethings go to the abstraction, some go to resources
			Running directly on the CPU/Memory, go straight to cpu, why? faster/simpler
			When does hypervisor come in?
			When you want to anything that normally requires privileges
			Change page tables
			Allocate memory
			Access the disk
			These get routed through the hypervisor
			How?
			Classic OS:
			Processes
			[System calls]
			OS - Kernel
			[Hypervisor (Provides a hardware-like interface to the Kernel)]
			Hardware

			Process interacts with the Kernel through System calls
			Function Call vs System
			Function is a jump to another bit of code in the address space
			Access space of the process
			System call
			Access something out of the address space
			Special CPU instruction / Software interrupt
			What is an interrupt?
			Are CPU mechanism which allows the CPU to be interrupted
			Logical equivalent to office talking to student. Someone knocks on the door. Hold on let me talk to him. (Interrupt)
			Not part of the normal execution path
			External signal
			Interrupt Table
			List of: Interrupt -> address
			Addresses here are the addresses in the Kernel Memory
			Normal CPU runs in usermode
			Usermode doesn't have access to all resources, CPU has supervisor mode, which see's everything
			**Code for interrupt runs in supervisor mode
			Keyboard presses, calls interrupt
			What is hardware virtualization?
			You give the Kernel a fake interrupt table
			Modern CPU support Hypervisor
			Whenever a privileged operation is run, it goes through the hypervisors Interrupt table.
			System call:
			Normally
			Userspace (proc)-> System call -> Kernel
			(Special Instruction, cpu changes to supervisor code)
			Hypervisor
			Userspace (proc) -> Hypervisor -> Kernel
			(Same as normal, but with middleman.

			Ring 0 - 3 Privledge levels on CPU
			Modern system has Ring -1 -> 3
			Ring -1 is the Hypervisor
			Allows the hypervisor to choose with Kerne gets the operation


			Guest knowing about the hypervisor is dangerou sin a secuirty sense
			Expanded interface, lines of communication that you didn't have before
			What prevents the guest from compromising the hypervisor?
			Information leakage
			Possible or prcoess to see the other kernels (Same physical memory / cpu)
			Language run times mostly just go through the abstraction and never have a direct connection to the resources

			JVM call some methods that have more provledgess that you do. Equivalents of sudo / setuid. All inside the same address space, enforce permission boundaries inside one address space, have to use software for midigation.

Soma: Created page with "==Audio== [https://homeostasis.scs.carleton.ca/~soma/systemssec-2018w/lectures/comp4108-2018w-lec20-26Mar2018.m4a Lecture 20 Audio] ==Notes=="

2018-03-28T17:50:16Z

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SystemsSec 2018W Lecture 20 - Revision history

Luc: /* Notes */

Soma: Created page with "==Audio== [https://homeostasis.scs.carleton.ca/~soma/systemssec-2018w/lectures/comp4108-2018w-lec20-26Mar2018.m4a Lecture 20 Audio] ==Notes=="