• Dates: 4/24-29/03
• Reading: Ch.18, Ch.19

Protection and Security: Concepts

• authorized vs. unauthorized access
• internal vs. external
• protection: typically internal
• security: typically external
• accidental vs malicious
  typically dealt in security
• files and other resources
  protection: mostly file focus
  security: general resources (data, code, etc.)
• security broader, more general
  mostly associate with higher integrity level
• our focus:
  mechanism/implementation to provide protection and security

Protection: Basics

• previous examples of protection
  • memory boundary check in memory management
    contiguous allocation
    segmentation
    (but not in paging, why?)
  • sharing and protection at page/segment/block level
  • file access in UNIX example

• protection concept
  • mechanism for access control
    authorized vs unauthorized
  • subject: programs, processes, or users
    access policies need to be followed
  • object: (general system) resources
    memory and file example above
    most often files
    hw and s/w objects
  • also: language based protection possible
    typing, boundary checking, etc.

• general goals of protection
  • basic: correct access control (above)
  • protect against incorrect access
  • mechanism to ensure access policies
• historical perspectives
  • single user/program: no need for protection
    full access to everything
  • multiprogramming: correct sharing
    not everything shared
  • previous examples
  • modern OS: general reliability
    guard against both accidental & malicious misuse

Protection Domain

• objects: h/w and s/w objects
• domain:
  • collection of objects
  • each with certain types of accesses
    access right: read, write, etc.
  • as viewed from users/processes
    domain implementation based on
    (in increasingly finer granularity) user, process, procedure
  • pairs: (object_i, access rights)
  • example: Fig 18.1 (p.631)
  • disjoint or overlapping
  • organization: domain structure

• domain structure
  • single domain
  • multiple domains
  • ring
    inner ones have more privileges
    example: MULTICS Fig 18.2 (p.634)
  • simplified ring
    example: UNIX file system protection
  • general overlapping: access matrix

• domain realization/implementation:
  • user,
  • process,
  • procedure (local variable, program scope)
  • (in increasingly finer granularity)
• related domain switching

Protection: Access Matrix

• general protection scheme: access matrix
  • row: domain
  • column: object (or resources)
  • cell: type of authorized accesses
• general domain structure
• example: Fig 18.3 (p.636)
• generalization: domain switching
  example: Fig 18.4 (p.637)
• other generalization: subdomain etc.

• types of access rights
  • related to access matrix
  • usually: read, write
  • other rights possible
  • associate with objects or domains
  • execute (Unix example: rwx)
  • copy, transfer, limited copy, etc
  • owner (can change access rights)
  • switch (domain switch)
  • subdomain

• implementation of access matrix
  • global table
  • access lists for objects
  • capability lists for domains
  • lock-key mechanism
• comparison
  • flexibility
  • level of protection
  • implementation overhead

Security

• security: extend protection to handle external problems as well
• security problem
  • intention: accidental vs. malicious
  • operation: reading/writing/destruction
• security measures: physical and user level
• authentication as a security measure
  • use of passwords
  • problems and alleviation
• program and system threats
  • Trojan horse/trap door
  • worms/viruses
• dealing with security threats
  • threat monitoring via audit log etc.
  • encryption

• SMU followup courses
  • computer security
  • network security
  • software security
  • related certificates

Exam Review

• scope and general information:
  • comprehensive but
  • more emphasis on material after Exam#2
  • 6 questions
  • 2 hours long
  • type of questions: similar to Exams #1 and #2 before
  • date: 5/7/03
  • time: 9-11am
  • location: same classroom.
  • video students: to be arranged with your proctor on or before 5/18/03.

• new topics:
  • files: more idea/concept, less implementation details
  • I/O: three generic methods and comparison
  • mass storage: focus on disk scheduling
  • distributed systems and distributed OS:
    general concepts,
    advantages,
    classification by service/topology/distance/protocol
  • distributed coordination, focus on:
    ME problem solutions
    deadlock handling
    event ordering
  • protection: concepts, access domain/matrix
  • security: general concepts/ideas, less on details

• comprehensive topics
• coordination/management of shared resources
  • logical conditions and how to ensure?
  • non-sharable: scheduling
  • allocation of shared resources
  • centralized vs distributed differences
• overall organization and management of resources
  • user vs. system views => mapping between the two
  • hierarchy and organization
  • physical resources: CPU, memory (frame/page), I/O (disk) scheduling
  • logical resources: processes, events, virtual memory, etc.
• overall understanding
• interconnection of similar ideas/solutions
  in different settings
  distributed vs single-CPU
  centralized solution possibility and drawbacks