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Message-ID: <201906032010.8E630B7@keescook>
Date: Mon, 3 Jun 2019 20:14:06 -0700
From: Kees Cook <keescook@...omium.org>
To: Alexander Potapenko <glider@...gle.com>
Cc: 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 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.)
--
Kees Cook
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