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Date: Thu, 27 Jun 2019 12:44:04 -0400
From: Qian Cai <cai@....pw>
To: Kees Cook <keescook@...omium.org>
Cc: Alexander Potapenko <glider@...gle.com>, Andrew Morton
<akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, Masahiro
Yamada <yamada.masahiro@...ionext.com>, Michal Hocko <mhocko@...nel.org>,
James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
Nick Desaulniers <ndesaulniers@...gle.com>, Kostya Serebryany
<kcc@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Sandeep Patil
<sspatil@...roid.com>, Laura Abbott <labbott@...hat.com>, Randy Dunlap
<rdunlap@...radead.org>, Jann Horn <jannh@...gle.com>, Mark Rutland
<mark.rutland@....com>, Marco Elver <elver@...gle.com>, linux-mm@...ck.org,
linux-security-module@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v9 1/2] mm: security: introduce init_on_alloc=1 and
init_on_free=1 boot options
On Thu, 2019-06-27 at 09:29 -0700, Kees Cook wrote:
> On Thu, Jun 27, 2019 at 09:25:11AM -0400, Qian Cai wrote:
> > On Thu, 2019-06-27 at 15:03 +0200, Alexander Potapenko wrote:
> > > +static int __init early_init_on_alloc(char *buf)
> > > +{
> > > + int ret;
> > > + bool bool_result;
> > > +
> > > + if (!buf)
> > > + return -EINVAL;
> > > + ret = kstrtobool(buf, &bool_result);
> > > + if (bool_result && IS_ENABLED(CONFIG_PAGE_POISONING))
> > > + pr_warn("mem auto-init: CONFIG_PAGE_POISONING is on, will
> > > take precedence over init_on_alloc\n");
> >
> > I don't like the warning here. It makes people think it is bug that need to
> > be
> > fixed, but actually it is just information. People could enable both in a
> > debug
> > kernel.
>
> How would you suggest it be adjusted? Should it be silent, or be
> switched to pr_info()?
pr_info() sounds more reasonable to me, so people don't need to guess the
correct behavior. Ideally, CONFIG_PAGE_POISONING should be renamed to something
like CONFIG_INIT_ON_FREE_CHECK, and it only does the checking part if enabled,
and init_on_free will gain an ability to poison a pattern other than 0.
Also, there might be some rooms to consolidate with SLAB_POSION as well.
>
> Also, doesn't this need to check "want_page_poisoning", not just
> CONFIG_PAGE_POISONING? Perhaps just leave the warning out entirely?
>
Yes, only checking CONFIG_PAGE_POISONING is not enough, and need to check
page_poisoning_enabled().
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