A Stealthy GPU-Based Keylogger (2013) [pdf]
cs.columbia.edu
cs.columbia.edu
I'm not a security expert, so could the binary kernel module for the NVIDIA driver be exploited for this effect?
But you are already able to load a module into the kernel, then you already have root level access and other, easier, options are open for you.
Because modules can be easily listed and therefor monitored, a change of the modules could trigger an alarm to the admin. So it isn't really stealthy either.