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

[Kaiwan N Billimoria]

On Tue, Jun 4, 2019 at 8:44 AM Kees Cook <keescook at chromium.org> wrote:
>
> 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 at linux-foundation.org> wrote:
> > >
> > > On Wed, 29 May 2019 14:38:11 +0200 Alexander Potapenko <glider at 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.)

(Pardon the gmail client)
How about:
- if (want_init_on_free())
-               pr_info("Clearing system memory may take some time...\n");
+  if (want_init_on_free())
+              pr_info("meminit: clearing system memory may take some
time...\n");

or even

+ if (want_init_on_free())
+                pr_info("meminit (init_on_free == 1): clearing system
memory may take some time...\n");

or some combo thereof?

--
Kaiwan
>
> --
> Kees Cook
>