[coreboot] Fwd: SimNOW VGA int 1a

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Fri Oct 17 00:07:35 CEST 2008

On 16.10.2008 23:54, ron minnich wrote:
> On Thu, Oct 16, 2008 at 2:52 PM, Carl-Daniel Hailfinger
> <c-d.hailfinger.devel.2006 at gmx.net> wrote:
>> If that's it, the solution is absolutely simple. And I mean totally simple.
>> 1. Backup old content
>> 2. Write ffffffff
> at this point it is game over.
> The code that does this is in rom.

Hm. Unshare only this function, maybe with another name?

>> 3. Read back and save in a variable
>> 4. Restore old content.
>> Make sure no code blacked out by the decode is executed between 1 and 4
>> and you're safe. If you're feeling paranoid, do it as inline asm. Make
>> sure that short sequence is never ever run as XIP code in ROM (I can do
>> that checking right now).
>> What am I missing?
> the big thing is that the problem code is a binary vga bios over which
> we have zero control. :-(

Hmmm. Is it running in vm86? If yes, we can trap I/O port writes and
reads, so this is solvable. Same should apply to x86emu.



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