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Date: Tue, 4 Jun 2019 11:31:26 +0530
From: Kaiwan N Billimoria <kaiwan@...wantech.com>
To: Kees Cook <keescook@...omium.org>
Cc: Alexander Potapenko <glider@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>, Dmitry Vyukov <dvyukov@...gle.com>, James Morris <jmorris@...ei.org>,
Jann Horn <jannh@...gle.com>, Kostya Serebryany <kcc@...gle.com>, Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>, Masahiro Yamada <yamada.masahiro@...ionext.com>,
Matthew Wilcox <willy@...radead.org>, Nick Desaulniers <ndesaulniers@...gle.com>,
Randy Dunlap <rdunlap@...radead.org>, Sandeep Patil <sspatil@...roid.com>,
"Serge E. Hallyn" <serge@...lyn.com>, Souptick Joarder <jrdr.linux@...il.com>, Marco Elver <elver@...gle.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux Memory Management List <linux-mm@...ck.org>,
linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v5 2/3] mm: init: report memory auto-initialization
features at boot time
On Tue, Jun 4, 2019 at 8:44 AM Kees Cook <keescook@...omium.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@...ux-foundation.org> wrote:
> > >
> > > On Wed, 29 May 2019 14:38:11 +0200 Alexander Potapenko <glider@...gle.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
>
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