Page Two

By Larry Seltzer  |  Posted 2004-05-25 Print this article Print

Its not like the idea of marking areas non-executable is a new one. Intels old 16-bit segmented model prior to the 386 had features for marking segments non-executable. Because of the nature of segments, this probably would have been worthless as a security feature, but clearly they were thinking about it over 20 years ago.

All is not perfect with NX yet. Microsoft says, for reasons I dont understand, that in 32-bit NX systems they will protect only the Windows stack, not the paged pool and other data areas. Incidentally, Linux has supported NX on AMD processors for a while now, although Im not sure whether the heap is protected.

I used to study microprocessors pretty closely, and NX seems like an obvious feature for page-level protection. The Page Table Entry (PTE), the data structure that describes a page, has lots of free "reserved" bits, and theyve been there for almost 20 years. Meanwhile, in an era where multigigahertz PCs cost less than $500 so that users can surf the Web and do word processing as fast as they could before, a major problem that could affect everyone went ignored. What other problems are being ignored like this one?

Intel especially should be ashamed. They had to be embarrassed into supporting NX in their upcoming Prescott processors after AMD added it to their own CPUs. And at first they resisted, expressing pointless concerns over compatibility problems that pale in comparison to the benefits of NX. Intel needs to take a good hard look at how they can make their processors better, rather than just faster.

Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983. Check out eWEEK.coms Security Center at for security news, views and analysis.
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Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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