> I tried to cat a string into the device (after compiling a new kernel
> with support for it, of course), and I could read it back. Great, I
> though. But when I rebooted, POST failed, the BIOS drive setup were
> horribly messed up, and suddenly I had a BIOS password.
> Apparently, /dev/nvram overwrites important BIOS configurations, surely,
> this isn't intended?
It absolutely *is* intended. The purpose of it is to read and possibly
modify the BIOS settings in NVRAM. If you do stupid things while root
(it *is* root-writeable-only, right?), Linux is not going to try to
save you.
Messing about with things in /dev that you don't understand is a good
way to mess up your system badly. (You're lucky that you didn't
have the /dev/bios patch installed and try playing with that.)
You can get a similar effect by sending strings to /dev/hda. They'll
read back, and your computer will work fine until the next time you try
to boot and discover that you just destroyed your boot sector and
partition table.
Other good things to play with if you want an unbootable system
are /boot/map, /vmlinuz, /sbin/init and /lib/ld.so
(BTW, most motherboards have a "reset the BIOS" jumper that you
install or remove for a few seconds, then you should be able
to boot with the factory default settings.)
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