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Goals of protection
The document discusses the goals and methods of computer protection. It aims to control access to resources and prevent their unauthorized use. Hardware protection differentiates between user and monitor modes. The CPU protects modes through a mode bit, and switches to monitor for interrupts. Memory protection prevents processes from accessing memory not allocated to them. I/O protection makes I/O instructions privileged to monitor mode only. The goals are to share resources safely according to policies and minimize damage from misbehaving programs.
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Introduces the concept of protection in computer security, focusing on the goals and hardware functionalities controlled by the operating system.
Discusses dual mode protection necessary for sharing resources in operating systems, ensuring incorrect programs don't mislead other executions.
Describes user mode and monitor mode in CPU operation, detailing the function of mode bits and interrupt management to switch execution modes.
Explains the timer role in system control, enabling time-sharing and tracking current time for efficient operating system management.
Highlights the significance of memory protection, ensuring that processes do not access unauthorized memory areas.
Focuses on I/O protection principles, preventing user programs from executing privileged instructions and ensuring safe resource use among users.
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Goals of protection
- 3. What is protection? Hardware protection? Goals of protection?
- 4. Protection is thesubset of computer security that deals with controlling , accessing and protecting the computer resources which is provided by operating system
- 5. Dual mode protection CPU protection Memory protection Input/output protection
- 6. Dual mode protection •Sharingsystem resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly. Provide hardware support to differentiate betweenat least two modes of operations.
- 7. 1. User mode executiondone on behalf of a user. 2.Monitor mode execution done on behalf of operating system.
- 8. Interrupt/fault monitor user Set user mode
- 9. Mode bit added to computer hardware to indicate the current mode: monitor (0) or user (1). When an interrupt or fault occurs hardware switches to monitor mode monitor Privileged instructions can be issued only in monitor mode.
- 10. . Timer - interrupts computer after specified period to ensure operating system maintains control. Timer commonly used to implement time sharing. g Timer also used to compute the current time.
- 11. Memory protection mainpurpose of memory protection is to prevent a process that has not been allocated to it
- 12. I/O Protection All I/Oinstructions are privileged instructions. Must ensure that a user program could never gain control of the computer in monitor mode (i.e., a user program that, as part of its execution, stores a new address in the interrupt vector ).
- 13. To prevent maliciousmisuse of the system by users or programs To ensure that each shared resource is used only in accordance with system policies, which may be set either by system designers or by system administrators. To ensure that errant programs cause the minimal amount of damage possible.