New, fundamental Intel Pentium flaw?

Rohit Khare (
Mon, 10 Nov 1997 13:07:13 -0800

Was the original poster implying that only some masks have this flaw --
"demand a new cpu"? Or is it genuinely worse?
I'd love to see the opcodes dissected -- where is this debate taking place
right now? I can imagine several mailing lists burning up over this one.

And the consequences ARE as bad as pda describes... it would be fun to
package this as an ActiveX control to tweak Intel AND Microsoft, no? :-)


My original reaction was:

Holy shit!

This is bad C code, but that's NO excuse for it to crash out a chip.
This *can't* have been in there all along, could it? Shit!


------- Forwarded Message

Date: Mon, 10 Nov 1997 11:07:35 -0500
From: "Philip A. DesAutels" <>
Subject: Intel Bug

This morning I received this message from the list
The sender was anonymous

> There is a SERIOUS bug in all pentium CPUs. The following
> code will crash any machine running on a pentium CPU, MMX or no
> MMX, any speed, regardless of OS (crash as in instant seize, hard
> reboot the only cure):
> char x [5] = { 0xf0, 0x0f, 0xc7, 0xc8 };
> main ()
> {
> void (*f)() = x;
> f();
> }
> This require no special permissions to run, it works fine with
> average-joe-userspace permissions. I have verified this, it works.
> Demand a new CPU from Intel.

Curious, I compiled that under Linux OS. Linux freezed. Dead.
Without *any* warning.

My machine is a Genuine Intel 166 MHZ Pentium MMX.

Then I rebooted Windows NT. Compiled it with my compiler system (lcc-win32).
Windows NT freezed. DEAD. Without *any* warning.

Then, I ported the code to my old faithful 486-DX33 with linux. Compiled it.
When it run it traps with 'illegal instruction'

This means that anybody can crash anytime any OS that runs under a Pentium
As the poster said, no special permissions are needed, the pentium runs under
ring 3 permissions!!!!

This means that no secure system can ever be built that uses the pentium CPU.
protected system. The OS receives NO TRAP!!!

This is absolutely incredible.

Bugs are impossible to avoid. Not even with huge corporations like Intel.
I will *not* start screaming at Intel now. Myself, I have done more bugs
than Intel ever will. As somene said before:

Those that are free of sin, throw the first stone...

For any user of pentium cpus in a multiuser system this means that
anybody that can execute a program can freeze the system dead. I repeat:

Philip A. DesAutels W3C <>
Technology and Society NE43-350 545 Technology Square
617.258.5714 Cambridge, MA 02139

------- End of Forwarded Message