Outline for May 4, 2000

  1. Greetings and felicitations!
  2. MULTICS ring mechanism
    1. MULTICS rings: used for both data and procedures; rights are REWA
    2. (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
    3. 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
  3. Propagated access control lists
  4. Discretionary AC Attacks: Trojan Horse
    1. overt - example edit a file
    2. covert - example delete all files
    3. a type of malicious logic (discuss this)
  5. Approaches
    1. Limited Protection Domain: (sandboxing)
    2. Name-checking subsystem; catches accesses not in pattern (startup, .asm, .obj)
    3. Other approaches

Send email to bishop@cs.ucdavis.edu.

Department of Computer Science
University of California at Davis
Davis, CA 95616-8562

Page last modified on 5/11/2000