In this post I'm going to talk about Remote Access in Legacy BIOS via serial console. I aware some (or most) of you are aware that BIOS has provided management console via serial port for a long time. I have the opportunity to modify a customer custom Geode board BIOS to add support for Serial Console a few years ago. It's a quite nifty but rather buggy implementation though (I meant the serial console module). This one is from AMIBIOS Core8. This is the screen shot from minicom in Arch Linux.
As you can see, the terminal looks like how you would expect it when accessed via real keyboard. Unfortunately, some function keys are not working as expected. You can configure the serial port just like you'd expect on old BIOS with serial port support, i.e. the BAUD rate, flow control, bit-ness (8-bit), etc.. The Remote Access menu in the picture is where one would configure the serial port setting for the remote access (serial console).
I'm "dusting-off" this old board from storage because it's quite a nice board to tinker with. I almost forgot that it has remote BIOS access feature back then. Basically, it works like Linux serial terminal in most embedded Linux boards out there. But, this one is limited. I think many enterprise-class motherboard has this feature back in the day and also today because it's a very crucial feature for remote manageability especially if you have thousands of machine to work with. Keep watching this one guys ;-). It's gonna be interesting..
Welcome to the dark corner of BIOS reverse engineering, code injection and various modification techniques only deemed by those immensely curious about BIOS