BIOS password...: probably on latitudes only

Mario Limonciello mario_limonciello at Dell.com
Tue Jul 22 10:17:30 CDT 2008


Andrea:

I've uploaded 4 fixes that were all attached to that bug that are being
processed right now.  If you (and anyone else that has encountered this
problem) could follow the directions on
https://wiki.ubuntu.com/Testing/EnableProposed

to update to the newer libsmbios and HAL packages and then comment on
that bug, that would be most appreciated.  After some positive feedback
is received with the new packages, they can be pushed to all machines.

A little background about the solution:
The current method of changing the backlight uses a BIOS call to
actually perform this backlight change on Linux.  On Windows, this
function isn't stubbed out at all per my understanding.  The ambient
light sensors of the laptop may be activated in Windows, but any
adjustments to the backlight are either done physically by pressing the
up and down buttons for the backlight or by the BIOS without interaction
with Windows.  On the Linux side, since these functions actually got
stubbed out, there is software support for changing the backlight.  The
BIOS can not be written to however, unless an authentication token is
obtained.  This token gets obtained by providing a user or admin BIOS
password.

What I did was provided another method to libsmbios that queries
directly if there is a type of password present.  I then added a check
to HAL to see if there is a BIOS password.  If there is, any attempts to
write to the backlight will not actually make the call into libsmbios,
but just return.  This will prevent the "lockups" that were encountered
when multiple calls to change the backlight were happening w/o valid
tokens.  Those were caused because making a query to change the BIOS
multiple times appeared to invoke an interrupt handler.

All in all, the negative side effect to this solution will be the fact
that any software utilities that would change the backlight won't work
when you have a BIOS password set.  They didn't work before either
though, so I don't see this as a regression.


Regards,

Andrea Ratto wrote:
> probably happens on latitudes (d series?) only...
>
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-- 
Mario Limonciello
*Dell | Linux Engineering*
mario_limonciello at dell.com

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