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Bugtraq archives for 3rd quarter (Jul-Sep) 1998: Re: A way to prevent buffer overflow exploits? (was: "Any user can

Re: A way to prevent buffer overflow exploits? (was: "Any user can

Brett Lymn (blymnBAEA.COM.AU)
Thu, 30 Jul 1998 10:51:59 +0930 

According to John D. Hardin:
>
>(to continue the topic drift, and throw some ideas into the pot...)
>
>I wonder how feasible it would be to modify GCC to generate code with two
>stacks (or something equivalent): one for local variables, the other for
>parameters and return addresses. Might moving the local variables away
>from the return addresses this way be a relatively cheap way to prevent
>buffer overflow exploits without having to recode all of the applications
>or using expensive bounds-checking?
>

It would be nice apart from the fact that Intel processors make the
concept inordinately difficult to implement.  Other CPU manufacturers
have had multiple general purpose stack registers for ages.  Motorola
had them in the 6809 even and they were used exactly in the manner
suggested by the compiler we were using at the time...

>Or how about allocating space for all local variables from the system heap
>automatically and transparently rather than placing them on the stack?
>

Managing memory on the heap will then be a major pain since it will
need to be done for each function call.  This would mean a major
performance hit.

>Or how about automatically allocating space just for local strings? This
>would take care of buffer overflows with minimal impact, wouldn't it?
>

In some languages, notably C, the concept of a string is a slippery
thing.  This is what the debate regarding C/Modula2/Ada/anythingbutgoddamC
was about.

--
Brett Lymn, Computer Systems Administrator, British Aerospace Australia
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