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

[Alexander Potapenko]

On Tue, Jun 4, 2019 at 8:01 AM Kaiwan N Billimoria
<kaiwan at kaiwantech.com> wrote:
>
> 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");
Yes, adding a prefix may give the users better understanding of who's
clearing the memory.
We should stick to the same prefix as before though, i.e. "mem auto-init"
>
> 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
> >



-- 
Alexander Potapenko
Software Engineer

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