Windows XP SP2 comes out with a nice security feature : Data Execution
Prevention (DEP). DEP is a mix of several techniques which all aim to
achieve some kind of anti-buffer overflow protection :

- Software : recompilation of system files with the /GS flag, etc.
- Hardware : DEP can use hardware-enforced protection, namely the NX bit
of AMD64 processors and the XD bit of latest Intel Pentium IV, to mark
memory pages as "non executable".

DEP can be enabled/disabled through Windows Control Panel, which has the
effect of setting the "/NoExecute=" kernel parameter inside "BOOT.INI".

According to the following article, PAE (Physical Address Extension)
mode must be enabled for using hardware supported DEP, but automatically
enabled if DEP is selected :
http://support.microsoft.com/kb/875352 

However, on my computer (Windows XP SP2 32-bit edition + AMD64 Athlon
3000+), hardware supported DEP does *not* work by default, even with 
"/NoExecute=AlwaysOn". I must add manually the "/PAE" boot parameter 
inside "BOOT.INI".

It means that using default XP SP2 installation, you do not benefit from 
"Enhanced Virus Protection"* even if you bought an AMD64, unless you 
edit manually the "system hidden read-only" file BOOT.INI.

* http://www.amd.com/us-en/Weblets/0,,7832_11104_11105,00.html 

Regards,
- Nicolas RUFF
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Security Consultant
EdelWeb (http://www.edelweb.fr/) 
Mail : nicolas.ruff (at) edelweb.fr
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