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As far as I read in a OS text book (Operating Systems by Silberschatz) Kernel mode is for privileged task, so it it true to claim that "User Level Thread can read/write Kernel threads" ?

Generally speaking, Is there any kind of protection between user and kernel level threads?

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No. In most operating systems, kernel memory is protected using virtual memory mechanisms, so a user process cannot read or write to kernel memory.

A user thread is part of a user process, and has the same permissions as the process. So, a user thread will not be able to write to kernel memory.

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Im not really sure, but this is my take on trying to guess what it could be from logical reasoning


  • A thread is a specific type of process. Generally speaking, any process in user mode will not be able to do any Kernel-mode operation.

  • However, threads have a shared memory system, and they don't know about each other (pipes between threads are a 3rd party communication through an "imaginary" file) and thus there should be no constraint on using the memory within a User-mode thread, even if it is shared with a Kernel-mode thread.

  • Its impossible to create a thread with Kernel-mode if you are in User-mode, but if you are in Kernel-mode you can change your privileges to be User-mode. Kernel code is usually trusted, and therefore creating a thread in User-space for a Kernel-mode process is probably still considered trusted.

So my guess is No, there is no protection.

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