vices, memory and is free to change registers that provide security at the hardware level.</p>
<p>Now, the code you write in <code>Ring 3</code> will typically have extremely restricted access to I/O and certain CPU registers (and instructions). Trying to issue an instruction or setting a register from <code>Ring 3</code> to change the <code>page table</code> will be prevented already at the CPU. The CPU will then then treat this as an exception and jump to the handler for that exception provided by the OS.