[PATCH v2 1/4] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options

[Alexander Potapenko]

On Fri, May 17, 2019 at 4:04 PM Michal Hocko <mhocko at kernel.org> wrote:
>
> On Tue 14-05-19 16:35:34, Alexander Potapenko wrote:
> > The new options are needed to prevent possible information leaks and
> > make control-flow bugs that depend on uninitialized values more
> > deterministic.
> >
> > init_on_alloc=1 makes the kernel initialize newly allocated pages and heap
> > objects with zeroes. Initialization is done at allocation time at the
> > places where checks for __GFP_ZERO are performed.
> >
> > init_on_free=1 makes the kernel initialize freed pages and heap objects
> > with zeroes upon their deletion. This helps to ensure sensitive data
> > doesn't leak via use-after-free accesses.
>
> Why do we need both? The later is more robust because even free memory
> cannot be sniffed and the overhead might be shifted from the allocation
> context (e.g. to RCU) but why cannot we stick to a single model?
init_on_free appears to be slower because of cache effects. It's
several % in the best case vs. <1% for init_on_alloc.

> --
> Michal Hocko
> SUSE Labs



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg