8836 Multics

Question 1

What is a process In multics?

Answer 1

A process is a collection of code and data segments that belong to a principal/user or running on their behalf.

Question 2

What are the two types of segments in multitics?

Answer 2

Users and supervisor segments.

Question 3

What are the two types of per segment access control in Multics?

Answer 3

List based
- Non-hierarchical
- inter-process
concentric rings of protection
- Hierarchical
- intra-process

Question 4

How is the ACL implemented for a segment in Multics.

Answer 4

A linked list containing.
-User identification
-Mode of Access
-Ring Brackets

Question 5

In Multics which rings may J access?

Answer 5

J+1,J+2,J+n

Question 6

What are the ring rules in Multics?

Answer 6

Rule1: A procedure segment in ring j can call any other procedure seegment in j or greater
Rule2: A procedure segment in ring j should only make controlled calls to a procedure seegment I I<J
Rule3: A procedure segment in ring j should not be given any access to data in lesser rings

Question 7

What is called when a ring crossing fault occurs?

Answer 7

Gatekeeper.

Question 8

How can a code segment (5,6,7) executing in a ring l+1 to m call a code segment (3,3,5) executing at k?

Answer 8

Via a gate in segment

Question 9

What happens when a code segment b is outside the call bracket l-m of a?

Answer 9

It cannot access the code segment a.

Question 10

In the ring bracket 0,63,63 what is the access bracket?

Answer 10

0-63 Since the access spans all the rings the segment gets loaded in the ring of the caller.

Question 11

What does the ring bracket of 5,48,48 mean on a Data segment with effective mode of RW?

Answer 11

Data can be written from ring 0-5, and read from 6-48, and it is not reachable from any code segment executing in a ring greater than 48.

Question 12

How do we decide which User proccess related procedures are allowed to access a Data segment?

Answer 12

Based on ACL.

Question 13

What can access a code segment with the ring bracket (3,3,5) and access mode R,E.

Answer 13

Code segments in rings 0-3 R,E and E through a gate:4-5
which code segment in what rings will be able to call the segment? 3
Which code Segments in which rings will never be able to call the segment? >5

Question 14

How do Modern operating systems differ in design from Multics?

Answer 14

Modern operating systems values portability over security.

Question 15

What is a way to structure various modules that make up a non-trivial TCB?

Answer 15

Layered Design.

Question 16

Which aspect of building a Trusted OS is most relevant to the discussion of Multitics ring-based Architecture?

Answer 16

The design aspect

Question 17

consider a multics Data Segment with ring Bracket (5,48,48) and effective mode RW. it means:

Answer 17

This Data Segment is RW for code executing in rings 0-5 but R only for code executing in rings 6-48

Question 18

Consider a Multics Code segment with ring bracket (0,1,63) and effective mode RE.

Answer 18

Code executing in ring 0 and ring 1 can call it without a crossing fault.
Code segments executing in rings 2 through 63 can make inward calls via a gate.

Question 19

Multics rings for TCB design are an example of this general design strategy:

Answer 19

Layered Design.