If I recall correctly Magic SYSRQ offered the ability to kill all running processes using a shortcut impossible to bypass (along with other shortcuts, like one

If I recall correctly Magic SYSRQ offered the ability to kill all running processes using a shortcut impossible to bypass (along with other shortcuts, like one for killing the X server 'no question asked' and no possibility whatsoever by X to dodge the kill -9). So basically you had to go first to a virtual console (in text mode) and then issue the Magic SYSRQ shortcut. That would kill all processes running on that console and you'd be sure to have a stock prompt without any kind of software keylogger. I don't know if Magic SYSRQ still exists or not for 64-bit Linuxes, it's been a while I haven't used it.