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SubjectRe: Pentium DEATH in user-mode
On Fri, 7 Nov 1997, Robert R. Collins wrote:

> Richard B. Johnson, you wrote:
> >
> >The following user-mode program will stop the internal clock
> >of a Pentium.
>
> Actually, it doesn't stop the internal clock. It sends out two
> (back-to-back) locked memory read cycles, without any intervening locked
> memory write cycles. This (most likely) causes the state machines of the
> chipsets to go bonkers. The net effect is a crashed system.
>
> >
> >char x[5]={0xf0,0x0f,0xc7,0xc8,0x00};

Well, according to my bus analyzer and an educated finger, the chip
stops __cold__ literly. The external chip temperature goes to
ambient from a nominal 22-28 degC above ambient and the power supply
load current goes way down.

All of these code-sequences cause the same effect.

0xf0,0x0f,0xc7,0xc8
0xf0,0x0f,0xc7,0xc9
0xf0,0x0f,0xc7,0xca
0xf0,0x0f,0xc7,0xcb
0xf0,0x0f,0xc7,0xcc
0xf0,0x0f,0xc7,0xcd
0xf0,0x0f,0xc7,0xce
0xf0,0x0f,0xc7,0xcf

I made a simple program to perform an exhaustive search of bad
opcodes that can crash a protected-mode system from user-mode.


Cheers,
Dick Johnson

Richard B. Johnson
Project Engineer
Analogic Corporation
Penguin : Linux version 2.1.60 on an i586 machine (66.15 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.


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