Outline for January 20, 2016

Reading: text, § 16 (15 in first edition)
Due: Presentation paper selection, Jan. 22; Project selection, Jan. 22; Homework 1, Jan. 25

  1. Access Control Lists
    1. Full access control lists
    2. UNIX method
    3. ACLs: describe, revocation issue
  2. Capabilities
    1. Capability-based addressing
    2. Inheritance of C-Lists
    3. Revocation: use of a global descriptor table
  3. MULTICS ring mechanism
    1. Rings, gates, ring-crossing faults
    2. Used for both data and procedures; rights are REWA
    3. (b1 b2) access bracket — can access freely; (b3, b4) call bracket — can call segment through gate; so if a’s access bracket is (32, 35) and its call bracket is (36, 39), then assuming permission mode (REWA) allows access, a procedure in:
      rings 0–31: can access a, but ring-crossing fault occurs
      rings 32–35: can access a, no ring-crossing fault
      rings 36–39: can access a, provided a valid gate is used as an entry point
      rings 40–63: cannot access a
    4. If the procedure is accessing a data segment d, no call bracket allowed; given the above, assuming permission mode (REWA) allows access, a procedure in:
      rings 0–32: can access d
      rings 33–35: can access d, but cannot write to it (W or A)
      rings 36–63: cannot access d

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