1.5. One issue related to execution of a guest supervisor environment within a h
ID: 663492 • Letter: 1
Question
1.5. One issue related to execution of a guest supervisor environment within a host environment on a single computer is the matter of hierarchical protection domains; in the simplest IA-32 ISA execution model, these often are termed in jargon as privilege rings, e.g., ring 0 through ring 3. In this simple ring jargon, in which ring does the host operating system kernel execute in a non-virtualized environment? In which ring does the guest operating system execute? What is a privileged instruction and how does VirtualBox handle such an instruction from the guest operating system?
Explanation / Answer
In ring 0 host operating system kernel execute in a non-virtualized environment.
The guest operating system executes either in ring 0 or in ring 3. In guest a virtual machine is active, so if the guest is running in ring 3 there is not much problem. The problem is how to interpret what the guest kernel is doing.
Priviliged instruction: It is the machine instruction. this type of instruction can only be executed when the processor runs in kernel mode.
VirtualBox has a different approach to handle instructions. When it runs in ring 0 kernel driver, it has set up most of its processes to run natively rather than on host operating system but when it comes to priviliged instructions it gets caught as these special instuctions utilize I/O registers. For the instruction to be calculated either VirtualBox should handle it on its own or it should delegate it to the host. If the VirtualBox handles the request on its own there can be the following possibilities, which are as follows.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.