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

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Message-ID: <CAAeHK+xog8-DP1o=1qqKgSP7Hii2Yjah6oyowNE3zSNVW5pRSw@mail.gmail.com>
Date:   Wed, 10 Mar 2021 13:52:04 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Kees Cook <keescook@...omium.org>,
        Alexander Potapenko <glider@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Popov <alex.popov@...ux.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jann Horn <jannh@...gle.com>,
        kernel-hardening@...ts.openwall.com,
        linux-hardening@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v5 3/7] init_on_alloc: Unpessimize default-on builds

On Tue, Mar 9, 2021 at 10:43 PM Kees Cook <keescook@...omium.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@...gle.com>
> Link: https://lore.kernel.org/lkml/CAG_fn=X0DVwqLaHJTO6Jw7TGcMSm77GKHinrd0m_6y0SzWOrFA@mail.gmail.com/
> Signed-off-by: Kees Cook <keescook@...omium.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()?