Pekka Enberg writes:
> On Thu, Feb 25, 2010 at 5:56 PM, Mikael Pettersson <mikpe@xxxxxxxx> wrote:
> > I fear that the only portable (across compiler versions) and safe
> > solution is to invoke an assembly-coded dummy function with prototype
> >
> > void use(void *p);
> >
> > and rewrite the code above as
> >
> > {
> > u32 temp[...];
> > ...
> > memset(temp, 0, sizeof temp);
> > use(temp);
> > }
> >
> > This forces the compiler to consider the buffer live after the
> > memset, so the memset cannot be eliminated.
>
> So is there some "do not optimize" GCC magic that we could use for a
> memzero_secret() helper function?
I guess there's some -fno-builtin-... that might achieve this effect,
but that would disable all memset optimizations, not just those affecting
sensitive data.
You'd want a function attribute or magic type annotation and apply it
only to the specific cases where it's needed. Alas, I know of no such
attribute or annotation. ('volatile' doesn't work, I tried that.)
Ask on gcc@xxxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-crypto" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
