Re: [RFC]: mm,power: introduce MADV_WIPEONSUSPEND

Michal Hocko
2020-07-13T08:02:11Z

On Sun 12-07-20 09:22:28, Pavel Machek wrote:
> On Tue 2020-07-07 12:00:41, Colm MacCarthaigh wrote:
> >
> >
> > On 7 Jul 2020, at 9:37, Pavel Machek wrote:
> > > Please go through the thread and try to understand it.
> > >
> > > You'd need syscalls per get_randomness(), not per migration.
> >
> > I think one check per get_randomness() is sufficient, though putting it at
> > the end of the critical section rather than the beginning helps.
>
> Yeah, well, one syscall is still enough to make it useless.

I am sorry but I really do not follow. Why would you want to call a
syscall on each get_randomness invocation? Why is it not enough to
simply have a flag that tells that an external event has happened
and reinitialize if the flag is set? Yes this wouldn't be really sync
operation but does that matter? Is using a few random numbers from the
old pool just because the notifier hasn't processed and flag the
situation a major security concern?

Btw. let me just clarify that I am not by any means pushing a solution
like that. All I am saying is that MADV_WIPEONSUSPEND is inherently
subtle interface that we likely want to avoid.
--
Michal Hocko
SUSE Labs