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What are the dangers of running programs in kernel mode?
Crashes in kernel mode are catastrophic; they will halt the entire PC. In User mode, the executing code has no ability to directly access hardware or reference memory. Code running in user mode must delegate to system APIs to access hardware or memory.
What does a program running in kernel mode have access to?
While processes run in kernel mode, they have unrestricted access to the hardware. The other mode is user mode, which is a non-privileged mode for user programs. Therefore, when a process runs in user mode, it has limited access to the CPU and the memory.
Which does not allow a process running in kernel mode to be permitted?
A preemptive kernel is where the kernel allows a process to be removed and replaced while it is running in kernel mode. A nonpreemptive kernel does not allow a process running in kernel mode to be preempted; a kernel-mode process will run until it exits kernel mode, blocks, or voluntarily yields control of the CPU.
Is a kernel process?
A kernel is bigger than a process. It creates and manages processes. A kernel is the base of an operating System to make it possible to work with processes.
What happens when you add a module to the kernel?
For example, assume we have added a module to the base kernel (i.e., we have modified our base kernel by recompiling it) and the module has a bug in it. This will cause error in system boot and we will never know which part of the kernel is causing problems.
Is the LKMs module part of the kernel?
**Warning: LKMs are not user space programs. They are part of the kernel. They have free run of the system and can easily crash it. So now that we have established the use loadable kernel modules, we are going to write a hello world kernel module.
Can a user mode program access the kernel?
Only in the same way that modprobe “defeats” security by loading new code into the kernel. For various reasons, sometimes it makes more sense to have semi-privileged code (like graphics drivers inside the X server) running in user-space rather than a kernel thread. Being able to kill it more easily, unless it locks up the HW.
Why are graphics drivers allowed in the kernel?
Baking graphics drivers into the kernel might reduce context switches between X clients and X server, like just one user->kernel->user instead of having to get data into another use-space process, but X servers historically are too big and too buggy to want them fully in kernel.