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this post was submitted on 02 Sep 2023
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Programming
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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..
dd if=/dev/zero of=/dev/sdais a userland program, which I would say causes harm./dev/sdaaccess requires superuser/root permissions from the kernel, which means asking the kernel to lift many of the protections.Yes, which is literally what OP is asking about. They mention system calls, and are asking, if a userland program can do dangerous thing using system calls, why is there a divide between user and kernel. "Because the kernel can then check permissions of the system call" is a great answer, but "hopefully you can't harm your computer with userland programs" is completely wrong and misguided.