why 'loading out-of-tree module taints kernel.' and 'example: module verification failed: signature and/or required key missing - tainting kernel'

[RevolverNeverJams]

dmesg | grep example report two 'warning' :' 1.loading out-of-tree module taints kernel.' and 2. 'example: module verification failed: signature and/or required key missing - tainting kernel' after I insmod example.ko,.
consequently, I couldn't find example in /dev

[alexforencich]

First one is self-explanatory. Loading a module that isn't part of the kernel sets a "taint" flag, and if you go ask the kernel devs to debug a crash they'll look at those flags and tell you to try again without any out-of-tree modules. This isn't really a warning so much as just an informational message. No way to avoid it aside from not using the kernel module.

Module verification is signature enforcement that's usually part of secure boot, but I think it can also be enabled separately. You'll either have to sign the module or disable secure boot/signature verification.