Which of the following instructions should be allowed only in kernel mode?

Hello friends, its a popular question Which of the following instructions should be allowed only in kernel mode? lets get the answer.

Which of the following instructions should be allowed only in kernel mode?

• Disable all interrupts
• Read the time-of-day clock
• Set the time-of-day clock
• Change the memory map

Answer:

In kernel mode, the executing code has complete and unrestricted access to the underlying hardware. It has the ability and permission to execute any of the CPU instructions and reference any memory address. The kernel mode is reserved for the lowest-level and the most trusted functions of the operating system. Hence it has the access to all the necessary functions to disable all interrupts when needed, set the time-of day clock and change the memory map as and when required, and these instructions should be allowed only in kernel mode.

These instructions mentioned above should not be accessed in user mode, but the reading of the time-of-day clock should be allowed in both the user and kernel mode.

Hence the answer is (a), (c) and (d).

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