Chapter 14 Protection

14.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005Goals of Protection software well-defined set of operations.. 14.6 Silberschatz, Galvin an

Chapter 14: Protection

14.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

computer system

are used to specify the resources a process may access

14.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Goals of Protection

software

well-defined set of operations

and only by those processes that are allowed to do so

Principles of Protection

privileges to perform their tasks

14.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Domain Structure

where rights-set is a subset of all valid operations that can be

performed on the object

Domain Implementation (UNIX)

● User

owner of the file being executed When execution completes user-id is reset

14.8 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Domain Implementation (MULTICS)

Access Matrix

■ Access(i, j) is the set of operations that a process executing in

14.10 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Access Matrix

Use of Access Matrix

must be in the access matrix

 owner of O i

 copy op from O i to O j

 control – D i can modify D j access rights

 transfer – switch from domain D i to D j

14.12 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Use of Access Matrix (Cont.)

agents and that rules are strictly enforced

Implementation of Access Matrix

Defines who can perform what operation

Domain 1 = Read, Write Domain 2 = Read

Domain 3 = Read 

Fore each domain, what operations allowed on what objects

Object 1 – Read Object 4 – Read, Write, Execute Object 5 – Read, Write, Delete, Copy

14.14 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Access Matrix of Figure A With Domains as Objects

Figure B

Access Matrix with Copy Rights

14.16 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Modified Access Matrix of Figure B

14.18 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Access Control

privilege

a system call

programs

Role-based Access Control in Solaris 10

14.20 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Revocation of Access Rights

■ Access List – Delete access rights from access list.

■ Capability List – Scheme required to locate capability in the system

before capability can be revoked

● Keys

Capability-Based Systems

system

program; system provides access protection for use of these rights

individual storage segments associated with object

through its protected procedures

14.22 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Language-Based Protection

high-level description of policies for the allocation and use of resources

enforcement when automatic hardware-supported checking is unavailable

protection system is provided by the hardware and the operating system

Protection in Java 2

JVM

cannot) perform

the stack is inspected to ensure the operation can be performed by the library

14.24 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 11, 2005

Stack Inspection

End of Chapter 14