Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory

Ingo Molnar
2015-11-29T15:39:26Z

* PaX Team <pageexec@freemail.hu> wrote:

> On 29 Nov 2015 at 9:08, Ingo Molnar wrote:
>
> >
> > * PaX Team <pageexec@freemail.hu> wrote:
> >
> > > i don't see the compile time vs. runtime detection as 'competing' approaches,
> > > both have their own role. [...]
> >
> > That's true - but only as long as 'this can be solved in tooling!' is not used as
> > an excuse to oppose the runtime solution and we end up doing neither.
>
> actually, i already voiced my opinion elsewhere in the constify thread on the
> kernel hardening list that adding/using __read_only is somewhat premature
> without also adding the compile time verification part (as part of the constify
> plugin for example). right now its use on the embedded vdso image is simple and
> easy to verify but once people begin to add it to variables that the compiler
> knows and cares about (say, the ops structures) then things can become fragile
> without compile checking. so yes, i'd also advise to get such tooling in
> *before* more __read_only usage is added.

I think you are mistaken there: if we add the page fault fixup to make sure we
don't crash if a read-only variable is accessed, then we'll have most of the
benefits of read-only mappings and no fragility - without having to wait for
tooling.

Thanks,

Ingo