PROTECTION

Goals of Protection:

• Protection : mechanism for controlling the access of the program, processes.
• It inproves reliability.

Principles of Protection

• Principle of least privilege
  • programs, users and systems should be given just enough privileges to perform their tasks.
  • this limits damage if entity has a bug or gets abused.
  • can be static or dynamic i.e. changed by process as needed.
    • ex: domain switching, privilege escalation
• Need to know: another similar concept like above.

For Protection :

• In Contiguous memory allocation system : we use limit registers.
• In Paging system : we use Page Table.
  • Each process has its own Page Table.
• In Segmentation system : we use Segmentation Table.
  • Each table is protected by base address and limit register.
• In Secondary Storage system : we have access rights .

Access Control :

• is a method that sets :
  • types of access given on different resources, under what cases, by whom.
• 3 basic Components :
  • Subjects (S) or Domain : set of entities having access to current object.
  • Objects (O) : set of resources that need access.
  • Rights (R) : set of Operations → that subjects can perform on object.
• Protection Domain : is a collection of object and access rights. (Permission -rwx-)

Access Control Policies (Rules)

• Discretionary Access Control

  • each object has a owner(subject/domain) which decides access rights there.
  • represented by access matrix. ,consist row and column.
  • describes which user has access to what object/resource.
  • row → current subject/domain
  • col → current object

  Uses of Access Matrix

  • It design separates mechanism from policy.
  • Mechanism(method)
    • OS provides access matrix + rules .
  • Policy (Rules)
    • User dictates policy , who can access and what

• Mandatory Access Control

  • System administrator enforce a policy for all users.

• Role-Based Access Control

  • based on what role user has in the system access control is there.

Domain Structure

• each column can be implemented as an access list.

domain is a set of access-rights.

• <object-name, rights-set>, right-set contains permissions.

Access Matrix

it is a representation of protection as a matrix.

• rows represent domains
• columns represent objects

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Implementation of Access Matrix

• Access Control List
  • created by dividing access-matrix column-wise.
• Capability List
  • created by dividing access-matrix row-wise.
    • divided into 2 fields:
      • Object descriptor
      • Access Rights

Operation on Access Matrix Entries

• Copy → allow access to be copied only within the column
  • denoted by *
  • copy from O_i to O_j
• Owner → allows addition or removal of acces rights.
  • make owner of O_i

Copy and Owner allows a process to change the entry in column.

• Control Right → used to change entries in a row.
  • D_i can modify D_j access rights
• transfer →  switch domains from D_i to D_j

Implementation of Access Matrix

• Global Table : it consists of a ordered set of triples <domain, object, right set>
  • if a triple is found → operation is allowed to continue, other wise error/exception.
  • Drawback :