This set of Microprocessor Multiple Choice Questions & Answers (MCQs) focuses on “Privilege”.
1. By using privilege mechanism the protection from unauthorized accesses is done to
a) operating system
b) interrupt handlers
c) system software
d) all of the mentioned
View Answer
Explanation: The operating system, interrupt handlers and other system softwares can be protected from unauthorized accesses in virtual address space of each task using the privilege mechanism.
2. The task privilege level at the instant of execution is called
a) Descriptor privilege level (DPL)
b) Current privilege level (CPL)
c) Effective privilege level (EPL)
d) None of the mentioned
View Answer
Explanation: Any one of the four privilege levels may be used to execute a task. The task privilege level at that instant is called the Current Privilege Level (CPL).
3. Once the CPL is selected, it can be changed by
a) hold
b) transferring control using system descriptors
c) transferring control using gate descriptors
d) transferring control using interrupt descriptors
View Answer
Explanation: Once the CPL is selected, it cannot be changed during the execution normally in a single code segment. It can only be changed by transferring the control, using gate descriptors, to a new segment.
4. The data segments defined in GDT (global descriptor table) and the LDT (local descriptor table) can be accessed by a task with
a) privilege level 0
b) privilege level 1
c) privilege level 2
d) privilege level 3
View Answer
Explanation: A task executing at level 0, the most privileged level, can access all the data segments defined in GDT and the LDT of the task.
5. A task with privilege level 0, doesn’t refer to all the lower level privilege descriptors in
a) GDT (global descriptor table)
b) LDT (local descriptor table)
c) IDT (interrupt descriptor table)
d) None of the mentioned
View Answer
Explanation: The task with privilege level 0, refers to all the lower level privilege descriptors which apply to all the descriptors except the LDT descriptors.
6. The selector RPL that uses a less trusted privilege than the current privilege level for further use is known as
a) Least task privilege level
b) Descriptor privilege level
c) Effective privilege level
d) None of the mentioned
View Answer
Explanation: A selector RPL uses a less trusted privilege than the current privilege level for further use. This is known as the Effective Privilege Level of the task.
7. The effective privilege level is
a) maximum numeric of RPL and CPL
b) minimum privilege of RPL and CPL
c) numeric minimum and privilege maximum of RPL and CPL
d) none of the mentioned
View Answer
Explanation: The effective privilege level is minimum in numeric and maximum in the privilege of RPL and CPL.
8. The task requesting an access to a descriptor is allowed to access after checking the
a) type of descriptor
b) privilege level
c) type of descriptor and privilege level
d) corresponding segment
View Answer
Explanation: The task requesting an access to a descriptor is allowed to access to it and to the corresponding segment, only after checking the type of the descriptor and privilege level(CPL, RPL, DPL).
9. A CALL instruction can reference only a code segment descriptor with
a) DPL less privilege than CPL
b) DPL equal privilege to CPL
c) DPL greater privilege than CPL
d) All of the mentioned
View Answer
Explanation: A CALL or JUMP instruction can reference only a code segment descriptor with DPL equal to CPL of the task or a segment with a DPL of equal or greater privilege than CPL.
10. The RPL of a selector that referred to the code descriptor must have
a) less privilege than CPL
b) greater privilege than CPL
c) equal privilege than CPL
d) any privilege regarding CPL
View Answer
Explanation: The RPL of a selector that referred to the code descriptor must have the same privilege as CPL.
11. The instruction that refers to only code segment descriptors with DPL equal to or less than the task CPL is
a) CALL
b) IRET
c) ESC
d) RET and IRET
View Answer
Explanation: The RET and IRET instructions are to refer to only code segment descriptors with DPL equal to or less than the task CPL.
12. When a JUMP instruction references a Task State Segment(TSS) descriptor, then DPL must be
a) equally privileged as CPL
b) greater or equally privileged than CPL
c) less or equally privileged than CPL
d) less privileged than CPL
View Answer
Explanation: When a CALL or JUMP instruction references a Task State Segment(TSS) descriptor, then DPL must be less or equally privileged than CPL.
13. The data segment access refers to
a) loading DS
b) loading ES
c) loading SS
d) all of the mentioned
View Answer
Explanation: Loading DS, ES or SS for referring to a new descriptor comes under the data segment access.
14. An exception is generated when
a) privilege test is negative
b) an improper segment is referenced
c) referenced segment is not present in physical memory
d) all of the mentioned
View Answer
Explanation: If the privilege test is negative or an improper segment is referenced then an exception 13 is generated. If the referenced segment is not present in physical memory, an exception 11 is generated.
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