kvm: module verification failed: signature and/or required key missing – tainting kernel

Instead of re-configuring the kernel, this error (module verification failed) could be resolved by just adding one line CONFIG_MODULE_SIG=n to the top of the Makefile for the module itself:

CONFIG_MODULE_SIG=n

# If KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq ($(KERNELRELEASE),)
    obj-m := hello.o

# Otherwise we were called directly from the command
# line; invoke the kernel build system.
else
    KERNELDIR ?= /lib/modules/$(shell uname -r)/build
    PWD := $(shell pwd)

default:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
endif