linux-kernel - Re: [PATCH v3 2/6] x86/mm/KASLR: Open code unnecessary function get

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Message-ID: <CAGXu5jKesZbrMWk6DOyMcpRr_JOLZF01umzXsf3BDueFFegqDQ@mail.gmail.com>
Date:   Sun, 17 Feb 2019 09:14:58 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        Mike Travis <travis@....com>,
        Thomas Garnier <thgarnie@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v3 2/6] x86/mm/KASLR: Open code unnecessary function get_padding

On Sat, Feb 16, 2019 at 6:02 AM Baoquan He <bhe@...hat.com> wrote:
>
> It's used only twice and we do bit shifts in the parent function
> anyway so it's not like it's hiding some uninteresting detail.
>
> Suggested-by: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Baoquan He <bhe@...hat.com>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  arch/x86/mm/kaslr.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> index d7c6e4e8e48e..bf680929fe26 100644
> --- a/arch/x86/mm/kaslr.c
> +++ b/arch/x86/mm/kaslr.c
> @@ -104,12 +104,6 @@ static __initdata struct kaslr_memory_region {
>         { &vmemmap_base, 1 },
>  };
>
> -/* Get size in bytes used by the memory region */
> -static inline unsigned long get_padding(struct kaslr_memory_region *region)
> -{
> -       return (region->size_tb << TB_SHIFT);
> -}
> -
>  /*
>   * Apply no randomization if KASLR was disabled at boot or if KASAN
>   * is enabled. KASAN shadow mappings rely on regions being PGD aligned.
> @@ -161,7 +155,7 @@ void __init kernel_randomize_memory(void)
>         /* Calculate entropy available between regions */
>         remain_entropy = vaddr_end - vaddr_start;
>         for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
> -               remain_entropy -= get_padding(&kaslr_regions[i]);
> +               remain_entropy -= kaslr_regions[i].size_tb << TB_SHIFT;
>
>         prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
>
> @@ -185,7 +179,7 @@ void __init kernel_randomize_memory(void)
>                  * Jump the region and add a minimum padding based on
>                  * randomization alignment.
>                  */
> -               vaddr += get_padding(&kaslr_regions[i]);
> +               vaddr += kaslr_regions[i].size_tb << TB_SHIFT;
>                 if (pgtable_l5_enabled())
>                         vaddr = round_up(vaddr + 1, P4D_SIZE);
>                 else
> --
> 2.17.2
>


-- 
Kees Cook