[vbox-dev] VM Memory space: region in BIOS - patching/override possible?

Mihai Hanor mhanor at yahoo.com
Tue May 31 14:34:08 GMT 2011

You can download the VirtualBox source and check the \src\VBox\Devices\PC\BIOS\rombios.c file. The lines you're interested in start with ".org 0xfff0" (the far jump), ".org 0xfff5" (the bios date) and ".org 0xfffe" (the system model id) - without the quotes. After modifying what you need, compile it.

Another way would be to patch an official binary. For example, search for "EA 5B E0 00 F0" as consecutive bytes, in VboxDD2.dll. With the 4.0.8 32 bit official win32 binary, you can find the last 16 bytes of the BIOS starting at 17338h. Use a hex editor to edit what you need.

If you need to modify the far jump, to match your particular real PC, it's better to recompile VirtualBox after you've made the appropriate modifications.

--- On Tue, 5/31/11, Arioch <the_Arioch at nm.ru> wrote:

> From: Arioch <the_Arioch at nm.ru>
> Subject: [vbox-dev] VM Memory space: region in BIOS - patching/override possible?
> To: vbox-dev at virtualbox.org
> Date: Tuesday, May 31, 2011, 3:29 PM
> Hello, all!
> i have an old box ( 128MB RAM, 13GB HDD, DOS + Win98 - and
> that is after
> several upgrades :-)  )
>      it has a DOS program, that can
> maybe never be used, but need to be kept
>      the program is copy-protected: is
> "attached" to last 16 bytes of BIOS,
> those F000:FFF0 to :FFFF
>      the rest of BIOS is not to be the
> key, but "BIOS creation date"
> definitely is.
>      Can this be reproduced in
> VirtualBox or VMLite ?
>      I mean that part of "stock" BIOS
> been replaced by pre-given data and,
> if
> possible, write-protected like BIOS on real hardware is ?
> // BTW, it does have some LPT port with key as well, but
> that's a
> different story, i hope :-)
>      i do not need the whole BIOS. only
> a little part.
>      last 16 bytes are reserved for
>      1) 5-bytes JMP FAR command, for
> CPU cold-start
>      2) the rest is BIOS creation date
> and is not code. I don't remember if
> in
> plain text or BCD or something.
>      Both these can be harmlessly
> patched, after virtual machine CPU
> kick-started.
>      But that may require some plugins
> creation (if there is proper API) or
> even some source patching, creating API/settings.
>      So, since you have knowledge of
> internals of VBox, i think u maybe can
> say.
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