Re: [PATCH v5 3/7] init_on_alloc: Unpessimize default-on builds

From: Kees Cook <keescook@chromium.org>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Elena Reshetova <elena.reshetova@intel.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Popov <alex.popov@linux.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Jann Horn <jannh@google.com>,
	kernel-hardening@lists.openwall.com,
	linux-hardening@vger.kernel.org,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	David Hildenbrand <david@redhat.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v5 3/7] init_on_alloc: Unpessimize default-on builds
Date: Wed, 10 Mar 2021 13:03:50 -0800	[thread overview]
Message-ID: <202103101303.6E6569C1@keescook> (raw)
In-Reply-To: <CAAeHK+xog8-DP1o=1qqKgSP7Hii2Yjah6oyowNE3zSNVW5pRSw@mail.gmail.com>

On Wed, Mar 10, 2021 at 01:52:04PM +0100, Andrey Konovalov wrote:
> On Tue, Mar 9, 2021 at 10:43 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > Right now, the state of CONFIG_INIT_ON_ALLOC_DEFAULT_ON (and
> > ...ON_FREE...) did not change the assembly ordering of the static branch
> > tests. Use the new jump_label macro to check CONFIG settings to default
> > to the "expected" state, unpessimizes the resulting assembly code.
> >
> > Reviewed-by: Alexander Potapenko <glider@google.com>
> > Link: https://lore.kernel.org/lkml/CAG_fn=X0DVwqLaHJTO6Jw7TGcMSm77GKHinrd0m_6y0SzWOrFA@mail.gmail.com/
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  include/linux/mm.h | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index bf341a9bfe46..2ccd856ac0d1 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2874,7 +2874,8 @@ static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
> >  DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
> >  static inline bool want_init_on_alloc(gfp_t flags)
> >  {
> > -       if (static_branch_unlikely(&init_on_alloc))
> > +       if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
> > +                               &init_on_alloc))
> >                 return true;
> >         return flags & __GFP_ZERO;
> >  }
> > @@ -2882,7 +2883,8 @@ static inline bool want_init_on_alloc(gfp_t flags)
> >  DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
> >  static inline bool want_init_on_free(void)
> >  {
> > -       return static_branch_unlikely(&init_on_free);
> > +       return static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,
> > +                                  &init_on_free);
> >  }
> >
> >  extern bool _debug_pagealloc_enabled_early;
> 
> Should we also update slab_want_init_on_alloc() and slab_want_init_on_free()?

Whoops! Thank you; I will update and resend. :)

-- 
Kees Cook