> is there a way to disable this BIOS function? More precisely, coreboot can be set to avoid
> receiving commands from GRUB and Ubuntu KERNEL?
If you build the following structure (please, do understand that this is very high level of presentation, which does not reflect reality 100%) on x86 architecture: FSP -> Coreboot -> Tiano Core [as payload], you might be able to avoid any/entirely legacy INT services.
In nutshell, Tiano Core dies after it passes control to the GRUB2. But... There are so called "run-time services" that Tiano Core sets, and passes them to Linux/WIN and these are alive through the life of the entire system.
I have no idea what these run time services are, actually (might be reminiscences of INT legacy...)! :-(
The similar use case if you use UEFI (so CSM is set OFF). Still, the same question remains: what are (WTF/WTH) "run time services"?
The other use cases are to do NSF mounting to these devices, but with Read ONLY attributes (on remote ARM system). So then you can copy files over to x86 based host system (having admin/root privileges) and inspect them, preserving (not compromising) originals.
All respective to x86 use cases.
You can also use Rpi 3, and mount these devices as RO (as already suggested). But this will not give you NTFS clear file accesses (for WIN HDD/SSD and USB storage systems).
> I hope I've been clear this time.
Well... I hope this clearly helps this time.
Zoran