Re: Shared memory DoS's

[howie () MS COM (Howard Kaye)]

Tops-20 had mapped memory segments before VMS was born.  It was called
PMAP back then (for Page Map).  I don't know if it had the same
vulnerability.

Howie Kaye

"Dick St.Peters" wrote:
> Mike Perry writes:
>
> > So as it turns out that it is in fact possible to create a DoS condition by
> > requesting a truckload of shared mem, then triggering pagefaults in the entire
> > shared region.
>
> Mapped memory segments have been susceptible to this since at least
> the early days of VMS, which AFAIK was the first OS to implement
> mapped memory (VMS used the term "mapped section").  I ran into this
> by accident no later than 1982 while doing image processing on a VMS
> system.  My processes run at the lowest possible priority (equivalent
> to the highest possible niceness), would effectively shut down the
> system until they completed.
>
> VMS didn't have a lot of tools for analyzing what was happening, but a
> few experiments quickly showed the culprit was page faulting.  Image
> processing tends to step through memory sparsely.
>
> Sorry - I no longer have an exploit :)
>
> --
> Dick St.Peters, stpeters () NetHeaven com
> Gatekeeper, NetHeaven, Saratoga Springs, NY
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