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Re: Buffer overflow prevention
From: Tom 7 <twm () andrew cmu edu>
Date: Fri, 15 Aug 2003 14:41:10 -0400 (EDT)


Crispin Cowan <crispin () immunix com> wrote:

Array bounds checking offers greater protection than any of these
protections (StackGuard, ProPolice, PointGuard, W^X, PAX/ASLR, etc.) The
problem is that the very fastest array bounds protection for C (Bounded
Pointers) imposes a 5X slowdown on performance, where as these other
techniques impose overheat somewhere between noise and 20%.

This may be true. Doing "safe" pointers in C is difficult because of
pointer arithmetic. But I think this is a bit unfair to bounds checking in
general--type safe compiled languages like ML achieve array bounds
checking (and other checks) at a much smaller penalty (less than 20% for
array-oriented code in my experience).  These languages also provide
protection against other common sources of holes, like integer overflow,
double-frees (most are garbage collected) and printf formatting attacks.
This protection is automatic and absolute; the only thing left to worry
about is bugs in the compiler, system library, and kernel (things that C
programmers already need to worry about, anyway).

In my opinion these languages are utterly practical for Unix network
daemons. Of course, this is a bit more work because you don't just
recompile the program, you have to rewrite it from scratch! But there are
other benefits to maintaining code in a modern, safe, high-level language.

 - Tom

 [ http://www.cs.cmu.edu/~tom7/ ]


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