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Date: Thu, 18 Apr 2019 15:02:46 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Laura Abbott <labbott@...hat.com>
Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>, James Morris <jmorris@...ei.org>, 
	"Serge E. Hallyn" <serge@...lyn.com>, 
	linux-security-module <linux-security-module@...r.kernel.org>, 
	Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Kostya Serebryany <kcc@...gle.com>, Dmitriy Vyukov <dvyukov@...gle.com>, Kees Cook <keescook@...omium.org>, 
	Sandeep Patil <sspatil@...roid.com>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2 2/2] initmem: introduce CONFIG_INIT_ALL_HEAP

On Mon, Apr 8, 2019 at 6:43 PM Laura Abbott <labbott@...hat.com> wrote:
>
> On 3/8/19 5:27 AM, Alexander Potapenko wrote:
> > This config option enables CONFIG_SLUB_DEBUG and CONFIG_PAGE_POISONING
> > without the need to pass any boot parameters.
> >
> > No performance optimizations are done at the moment to reduce double
> > initialization of memory regions.
> >
> > Signed-off-by: Alexander Potapenko <glider@...gle.com>
> > Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > Cc: James Morris <jmorris@...ei.org>
> > Cc: "Serge E. Hallyn" <serge@...lyn.com>
> > Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> > Cc: Kostya Serebryany <kcc@...gle.com>
> > Cc: Dmitry Vyukov <dvyukov@...gle.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Sandeep Patil <sspatil@...roid.com>
> > Cc: linux-security-module@...r.kernel.org
> > Cc: linux-kbuild@...r.kernel.org
> > Cc: kernel-hardening@...ts.openwall.com
> > ---
> >   mm/page_poison.c         |  5 +++++
> >   mm/slub.c                |  2 ++
> >   security/Kconfig.initmem | 11 +++++++++++
> >   3 files changed, 18 insertions(+)
> >
> > diff --git a/mm/page_poison.c b/mm/page_poison.c
> > index 21d4f97cb49b..a1985f33f635 100644
> > --- a/mm/page_poison.c
> > +++ b/mm/page_poison.c
> > @@ -12,9 +12,14 @@ static bool want_page_poisoning __read_mostly;
> >
> >   static int __init early_page_poison_param(char *buf)
> >   {
> > +#ifdef CONFIG_INIT_ALL_HEAP
> > +     want_page_poisoning = true;
> > +     return 0;
> > +#else
> >       if (!buf)
> >               return -EINVAL;
> >       return strtobool(buf, &want_page_poisoning);
> > +#endif
> >   }
> >   early_param("page_poison", early_page_poison_param);
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 1b08fbcb7e61..00e0197d3f35 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1287,6 +1287,8 @@ static int __init setup_slub_debug(char *str)
> >       if (*str == ',')
> >               slub_debug_slabs = str + 1;
> >   out:
> > +     if (IS_ENABLED(CONFIG_INIT_ALL_HEAP))
> > +             slub_debug |= SLAB_POISON;
> >       return 1;
> >   }
> >
>
> I've looked at doing something similar in the past (failing to find
> the thread this morning...) and while this will work, it has pretty
> serious performance issues. It's not actually the poisoning which
> is expensive but that turning on debugging removes the cpu slab
> which has significant performance penalties.
>
> I'd rather go back to the proposal of just poisoning the slab
> at alloc/free without using SLAB_POISON.
Hi Laura,

May I wonder what were the performance numbers you were seeing?
I've found this patch:
https://www.openwall.com/lists/kernel-hardening/2016/01/26/1, but
that's around 100% slowdown.
> Thanks,
> Laura
>
>
> > diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
> > index 27aec394365e..5ce49663777a 100644
> > --- a/security/Kconfig.initmem
> > +++ b/security/Kconfig.initmem
> > @@ -13,6 +13,17 @@ config INIT_ALL_MEMORY
> >
> >   if INIT_ALL_MEMORY
> >
> > +config INIT_ALL_HEAP
> > +     bool "Initialize all heap"
> > +     depends on INIT_ALL_MEMORY
> > +     select CONFIG_PAGE_POISONING
> > +     select CONFIG_PAGE_POISONING_NO_SANITY
> > +     select CONFIG_PAGE_POISONING_ZERO
> > +     select CONFIG_SLUB_DEBUG
> > +     default y
> > +     help
> > +       Enable page poisoning and slub poisoning by default.
> > +
> >   config INIT_ALL_STACK
> >       bool "Initialize all stack"
> >       depends on INIT_ALL_MEMORY
> >
>


-- 
Alexander Potapenko
Software Engineer

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