Re: [PATCH v5 2/3] mm: init: report memory auto-initialization features at boot time

Kees Cook
2019-06-04T03:14:12Z

On Mon, Jun 03, 2019 at 11:24:49AM +0200, Alexander Potapenko wrote:
> On Sat, Jun 1, 2019 at 3:18 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Wed, 29 May 2019 14:38:11 +0200 Alexander Potapenko <glider@google.com> wrote:
> >
> > > Print the currently enabled stack and heap initialization modes.
> > >
> > > The possible options for stack are:
> > > - "all" for CONFIG_INIT_STACK_ALL;
> > > - "byref_all" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL;
> > > - "byref" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF;
> > > - "__user" for CONFIG_GCC_PLUGIN_STRUCTLEAK_USER;
> > > - "off" otherwise.
> > >
> > > Depending on the values of init_on_alloc and init_on_free boottime
> > > options we also report "heap alloc" and "heap free" as "on"/"off".
> >
> > Why?
> >
> > Please fully describe the benefit to users so that others can judge the
> > desirability of the patch. And so they can review it effectively, etc.
> I'm going to update the description with the following passage:
>
> Print the currently enabled stack and heap initialization modes.
>
> Stack initialization is enabled by a config flag, while heap
> initialization is configured at boot time with defaults being set
> in the config. It's more convenient for the user to have all information
> about these hardening measures in one place.
>
> Does this make sense?
> > Always!
> >
> > > In the init_on_free mode initializing pages at boot time may take some
> > > time, so print a notice about that as well.
> >
> > How much time?
> I've seen pauses up to 1 second, not actually sure they're worth a
> separate line in the log.
> Kees, how long were the delays in your case?

I didn't measure it, but I think it was something like 0.5 second per GB.
I noticed because normally boot flashes by. With init_on_free it pauses
for no apparent reason, which is why I suggested the note. (I mean *I*
knew why it was pausing, but it might surprise someone who sets
init_on_free=1 without really thinking about what's about to happen at
boot.)

--
Kees Cook