On 20 May 2019, at 5:28, Kevin O'Connor <kevin@koconnor.net> wrote:

On Fri, May 17, 2019 at 11:57:23PM +0300, Sam Eiderman wrote:

From: Liran Alon <liran.alon@oracle.com>

Windows kernel extracts various BIOS information at boot-time.
The method it uses to extract SystemBiosDate is very hueristic.
It is done by nt!CmpGetBiosDate().

nt!CmpGetBiosDate() works by scanning all BIOS memory from 0xF0000 to
0xFFFF5 (FSEG) in search for a string which is formatted like a date.
It then chooses the string which represents the most recent date, and
writes it to:

   HKLM/HARDWARE/DESCRIPTION/System SystemBiosDate

This date should usually be BiosDate located at FSEG(0xFFF5).

FWIW, if you want to ensure a stable date is found, it's probably
simpler to force a valid date string to be present in the f-segment.
Something like: char win_bios_date[] VARFSEG = " 04/01/2014 ";

As with my previous emails, I'd recommend using a hard-coded date (not
a build date) - as this tends to improve reproducibility.

The thing is, if the date reported by smbios tables is 05/02/2015 (which is

bigger than 04/01/2014) so:

• If smbios tables are in fseg - Windows will select the most recent date - 05/02/2015
• If not - Windows will select the most recent date (the only one it found) -  04/01/2014

So 'char win_bios_date[] VARFSEG = " 04/01/2014 “‘ will not help.

Sam

-Kevin

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