Security vulernarability or security feature?

[Robert C. Seacord]

Ralph,

Comments below.

> (a) Arithmetic overflows have historically been a significant source of
> security vulnerabilities.
>   
agreed.
> (b) Recent versions of gcc (along with other compilers) contain an
> optimisation that can *REMOVE* arithmetic overflows.
>   
I am very interested in seeing how this optimization can remove 
arithmetic overflows.

If you can send me an example of source code and instructions on how to 
build, I would certainly be happy to promote this feature of gcc on our 
secure coding web site.

> Why is Cert advising people to avoid an optimisation that can ---
> realistically, although probably rarely --- remove security
> vulnerabilities?
>   
If you are referring to VU#694123, this refers to an optimization that 
removes checks pointer arithmetic wrapping.  The optimization doesn't 
actually eliminate the wrapping behavior; this still occurs.  It does, 
however, eliminate certain kinds of checks (that depend upon undefined 
behavior).

Thanks,
rCs