Even if you do compile the kernel yourself, do you really own your OS if you haven't compiled the compiler yourself? Did you use a pre-built compiler binary to compile the compiler?

Now we're getting to the real questions in life. :)

(Incidentally, this is probably the most fundamental software supply chain attack vector - manipulate the compiler binary used to compile the compiler used to compile the kernel and userspace. The attack payload would never appear in any sources, but would always be present in binaries.)