this post was submitted on 02 Sep 2023
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Programming

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Why do we have two modes in cpu(user and kernel) since we still can still easily harm computer with userland programs? (lemm.ee)
submitted 1 year ago* (last edited 1 year ago) by SmoothSurfer@lemm.ee to c/programming@beehaw.org
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I have never dug into low level things like cpu architectures etc. and decided to give it a try when I learned about cpu.land.

I already was aware of the existence of user and kernel mode but while I was reading site it came to me that "I still can harm my system with userland programs so what does it mean to switch user mode for almost everything other than kernel and drivers?" also we still can do many things with syscalls, what is that stopping us(assuming we want to harm system of course) from damaging our system.

[edit1]: grammar mistakes

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[–] jarfil@beehaw.org 1 points 1 year ago

That's interesting, I don't have much contact with Apple's ecosystem.

Sounds similar to a setup that Linux allows, with the root filesystem on btrfs, making a snapshot of it and updating, then live switching kernels. But there is no firmware support to make the switch, so it relies on root having full access to everything.

The hypervisors approach seem like what Windows is doing, where Windows itself gets booted in a Hyper-X VM, allowing WSL2 and every other VM to run at "native" speed (since "native" itself is a VM), and in theory should allow booting a parallel updated Windows, then just switching VMs.

On Linux there is also a feature for live migrating VMs, which allows software to keep running while they're being migrated with just a minimum pause, so they could use something like that.