dmidecode is a tool for reading loads of platform registers, it is obviously not the only way to do it, or even the intended way really. Riot has almost certainly implemented the functionality from scratch in their anticheat, it’s a relatively trivial thing to do.

What I've read just now is what I'd deliberately not gone looking for up to this point in case I found this out.

Linux and Windows happen to require that the executables that access that information be run with root privileges, but it looks like that's merely an affectation.

It seems that any old piece of software, without root or other privileges, can independently run the CPUID instruction that obtains a processor's serial number.

I do not like this one bit.

You at least could in the past, I haven't had to do it in a while. Seems like the command would just be "dmidecode", with grep if you're looking to automate it

This is not running it as root (i.e. privileged userland, still ring 3), this is running it as ring 0 (i.e. the level that the kernel runs at, with no restrictions on access to memory and hardware at all). A tiny bug in ring 0 code can take down the system or open security vulnerabilities, where the kernel can provide more hardening to protect applications to an extent.

You could say this is the inner circle of hell.

They would not.

Anyone doing anti-cheat stuff tries to keep it as secret as possible, so that the cheaters have a more difficult time working around it.

Either I knew and forgot, or misunderstood it as CPU family identification whenever I've come across it. Denial is also a possibility. We'll see if I remember this in a month or two.