3 ms·

Thats interesting. I've booted UEFI machines using PXE and judging from the PXE ROM versions displayed, the PXE code hasn't changed much, on my boxes at least.

by drvdevd 10y ago

Thats interesting. I've booted UEFI machines using PXE and judging from the PXE ROM versions displayed, the PXE code hasn't changed much, on my boxes at least. I would agree that UEFI is an OS of its' own. But thats the whole point isn't it? That way writing drivers for peripherals can be done in C, etc. I have a BIOS machine I cant boot using my SD card for example, which I need to do. I imagine writing (or porting) a driver for UEFI to interface with that SD card reader would be an order of magnitude simpler than doing the same by modifying my BIOS (which I've seriously considered doing).

userbinator 10y ago
If you really want to boot from an SD card, try putting it in a standard USB card reader. Booting from USB mass storage has been supported for over a decade in BIOS, well before UEFI. Otherwise, if you want to actually integrate a driver for an internal SD card reader (which isn't a USB one) into the BIOS, then an Option ROM (INT 13H hook) would be the way to go.
rasz_pl 10y ago
Go ahead. Try writing a custom uefi module, I dare you. Its such a complicated mess it takes a team, and still you end up with blinders on every corner(intel reference code full of bugs etc).
- drvdevd 10y ago
  I have no doubt that its a mess. I suppose I've just bought into the hype about what (U)EFI was supposed to be when it came along. Maybe one day it or something like it will make this all easier.
kijiki 10y ago
The BIOS way to do this is with an Option ROM. During boot, the BIOS scans for a special signature, and jumps to a fixed offset in that block. The OPROM init routine then hooks the various software interrupts that the BIOS, boot-loader and other OPROMs use to read from disk. You can inject a custom one into your BIOS image, but if you have PCI/PCIe available, you can get cards that have an OPROM onboard. The easiest/hacky way is an old NIC that someone has reverse engineered enough to flash its OPROM; you're just using it for the OPROM, the NIC functionality is unused.
- drvdevd 10y ago
  Very interesting thank you. You may already be aware, but when I first saw the replies here mentioning Option ROMs I immediately thought of the thunderstrike EFI vulnerabilities for Macbooks. I've yet to actually mess with them, but apparently that was how they worked at least in the first generation, I haven't followed the research much further yet [https://trmm.net/Thunderstrike https://trmm.net/Thunderstrike]. So since option ROMs, for obvious reasons, survived the "transition" to EFI, does this mean the same mechanism could be used in BIOS machines? At least this might also have implications for backporting peripheral drivers too (for whatever reason)...

by drvdevd 10y ago

userbinator 10y ago

If you really want to boot from an SD card, try putting it in a standard USB card reader. Booting from USB mass storage has been supported for over a decade in BIOS, well before UEFI. Otherwise, if you want to actually integrate a driver for an internal SD card reader (which isn't a USB one) into the BIOS, then an Option ROM (INT 13H hook) would be the way to go.

rasz_pl 10y ago

Go ahead. Try writing a custom uefi module, I dare you. Its such a complicated mess it takes a team, and still you end up with blinders on every corner(intel reference code full of bugs etc).

drvdevd 10y ago
I have no doubt that its a mess. I suppose I've just bought into the hype about what (U)EFI was supposed to be when it came along. Maybe one day it or something like it will make this all easier.

kijiki 10y ago

The BIOS way to do this is with an Option ROM. During boot, the BIOS scans for a special signature, and jumps to a fixed offset in that block. The OPROM init routine then hooks the various software interrupts that the BIOS, boot-loader and other OPROMs use to read from disk. You can inject a custom one into your BIOS image, but if you have PCI/PCIe available, you can get cards that have an OPROM onboard. The easiest/hacky way is an old NIC that someone has reverse engineered enough to flash its OPROM; you're just using it for the OPROM, the NIC functionality is unused.

drvdevd 10y ago
Very interesting thank you. You may already be aware, but when I first saw the replies here mentioning Option ROMs I immediately thought of the thunderstrike EFI vulnerabilities for Macbooks. I've yet to actually mess with them, but apparently that was how they worked at least in the first generation, I haven't followed the research much further yet [https://trmm.net/Thunderstrike https://trmm.net/Thunderstrike]. So since option ROMs, for obvious reasons, survived the "transition" to EFI, does this mean the same mechanism could be used in BIOS machines? At least this might also have implications for backporting peripheral drivers too (for whatever reason)...