Operating System Security Assignment NO PDF

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Operating system security...

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Operating System Security Assignment no. 4 Student Id: 8671947

1. What requirements is memory management intended to satisfy? Ans: The requirements that the memory management should satisfy are:

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Protection, Relocation, physical Organization, Local Organization and Sharing.

2. Why is it not possible to enforce memory protection at compile time? Enforcing Memory protection during the compile time of any program is difficult and not possible because the program location is not known and cannot be predicted in the main memory. Also the most programming languages uses dynamic allocation and calculation of address at the run time of the program. So it is not possible to check absolute address of program and data at compile time. Example: Pointers into data structure. Ans:

3. Why is the capability to relocate processes desirable? Ans: It is desirable capability because the programmer doesn’t know that which other programs can be in the main memory at the execution time of the current program. Also, it is likeable to swap the active processes out and in from the memory so that it maximizes the utilization of the processor by giving the large number of ready processes to be executed. The location of the processes in the main memory is not predictable. 4. What are the distinctions among logical, relative, and physical addresses? Ans: Logical address: It’s points to a memory location which is independent of the current assignment of the data to the specific memory. Relative Address: The address is expressed as a location which is related to some already known point mostly the at the beginning of the program. Physical Address: It is also called as Absolute address, this is the real location that is in the main memory. 5. What is the difference between Internal and External Fragmentation? Ans: External Fragmentation is done when the memory is divided in the variable size of partition based on the process size. Internal Fragmentation occurs when the memory is divided into the fixed sized partitions. External Fragmentation happens when the free memory is separated into small blocks and gets scattered in the allocated memory. Internal Fragmentation happens when the size of the memory assigned is larger than the memory required by the process and this makes the free space and causes Internal Fragmentation.

6. Explain thrashing. Typically, what does the presence of “thrashing” indicate about the computer experiencing it? Ans: When the virtual memory resources are over used then thrashing occurs. It leads to the constant state of the page faults and paging. Thrashing reduces the performance of the computer. When the virtual memory exchanges data for data from the hard disk rapidly this causes the high access rate of hard disk and the computer experiences the degradation in the performance as the state of paging becomes constant.

7. Why is the principle of locality crucial to the use of virtual memory? Ans: Principal of locality: It is the tendency of the processor which makes it to access the set of same memory location again and again for the small amount of time. It is very important for the use of virtual memory because it states that data and program references in a process tends to the cluster. This indicates that only few pieces of process is required for a short amount of time.

8. In your own words, briefly explain how NX (non-executable stack) protects against exploitation of stack-based buffer overflows. Ans:

9. Describe the distinction between spatial and temporal locality. Ans: Spatial Locality: It is the execution tendency which involve many amount of memory locations which are gathered and clustered. Temporal Locality: It is the processors tendency to which makes it to access the memory locations which have been already and recently used....