DDoS in FreeBSD 6.2-STABLE And Problen With The Clock

Chuck Swiger cswiger at mac.com
Mon Jun 11 20:54:29 UTC 2007


On Jun 11, 2007, at 10:46 AM, Kevin K. wrote:
>> There are some problems, first DDoS (hardware DDoS) in the system.
>
> I'd like to know what you mean by "hardware DDoS"

I'm not sure what the OP meant, but I can provide examples of a  
hardware DDoS.

Way back when, certain machines were equipped with a Motorola/TI  
56001 DSP, which had three separate, parallel execution units, and  
was an early example of SIMD/VLIW design.  It turns out that if you  
issued an instruction to all three pipelines [1] which loaded or  
saved to the same memory address, you would fry the DSP chip.  The  
compiler used to generate the code for the 56K DSP chip would prevent  
this unfortunate event by reordering instructions if needed, but if  
you wrote your own assembly, you could in fact do a hardware DDoS if  
you weren't careful.  :-)

-- 
-Chuck

[1] IIRC, it could deal with two pipelines hitting the same address,  
but not all three.



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