Severity of ACPI Error Message from _SRS

[Colin Ian King]

On 25/01/13 09:22, Alex Hung wrote:
> Hi,
>
> It is found that kernel generates ACPI error messages on AMI's BIOS's
> implementation when kernel executes _SRS messages, as the launchpad bug
> below
>
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1076979
>
> Apparently kernel follows ACPI specification but BIOS did not handle it
> correctly; however, the error messages has not caused function failure
> so far.
>
> Some facts:
> 1. It is only seen on AMI's BIOS
> 2. S3, S4, and reboot failures are not related to this errors so far.
> 3. It only happens on super I/O devices, i.e. LPT (for printer port) and
> UART (for serial port) that reside in LPC bridge.
> 4. _SRS method is optional.
> 5. BIOS usually configures LPT and UART, if presents, during *POST* time.
> 6. We haven't seen LPT or UART failures even when the ACPI errors are
> presents.
>
> For longer term, it is needed to feedback BIOS vendor to have this fixed.
>
> For now, the failures are marked as CRITICAL. It is suggested that we
> may lower it to HIGH or MEDIUM. I personally think it is not a bad idea
> for the reasons above.
>
> Any thoughts?
>
> Cheers,
> Alex Hung
>
>
The reason that this is marked CRITICAL is that the firmware is given a 
buffer that is too short and we have an attempt to access memory outside 
this buffer.  fwts doesn't care about which control this happens to, any 
access outside an buffer is really not good, so it is marked as so.

I consider this as bad as a buffer overflow in C - although in this case 
the interpreter is able to catch so we don't actually crash and burn. 
The issue is that the code is trying to set something which can't be set 
- and so the interpreter can't do it and the end result is something 
that isn't working correctly.  fwts has to make a best guess judgement 
and flags this up as critical for a few reasons:

1. The code is obviously badly wrong
2. An attempt to write to memory outside a given range is always a bad bug
3. The end result is that the action is aborted, so who knows what the 
end result will be, the outcome is not predictable.

Hence why it is flagged as critical, so that somebody will look at it 
and see why it is failing so miserably ;-)

Colin