linux-kernel - Re: [PATCH v2 2/5] init_on_alloc: Unpessimize default-on builds

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Date:   Thu, 26 Mar 2020 16:48:41 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Kees Cook <keescook@...omium.org>
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>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jann Horn <jannh@...gle.com>,
        "Perla, Enrico" <enrico.perla@...el.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arm-kernel@...ts.infradead.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] init_on_alloc: Unpessimize default-on builds

On Tue, Mar 24, 2020 at 9:32 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.
>
> 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 059658604dd6..64e911159ffa 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2665,7 +2665,8 @@ static inline void kernel_poison_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) &&
>             !page_poisoning_enabled())
>                 return true;
>         return flags & __GFP_ZERO;
> @@ -2674,7 +2675,8 @@ 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) &&
>                !page_poisoning_enabled();
>  }
>
> --
> 2.20.1
>
Reviewed-by: Alexander Potapenko <glider@...gle.com>

-- 
Alexander Potapenko
Software Engineer

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