this post was submitted on 02 Sep 2023
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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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[–] farcaster@beehaw.org 28 points 1 year ago (9 children)

Well hopefully you can't harm your computer with userland programs. Windows is perhaps a bit messy at this, generally, but Unix-like systems have pretty good protections against non-superusers interfering with either the system itself, or other users on the system.

Having drivers run in the kernel and applications run in userland also means unintentional application errors generally won't crash your entire system. Which is pretty important..

[–] duncesplayed@lemmy.one 1 points 1 year ago (5 children)

dd if=/dev/zero of=/dev/sda is a userland program, which I would say causes harm.

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

Yeah, security is in layers and userland isn't automatically "safe", if that's what you're pointing out. So I did mention non-superusers. Separating the kernel from userland applications is also critically important to (try to) prevent non-superusers from accessing APIs and devices which only superusers (or those in particular groups) are able to reach.

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