linux-kernel - Re: [kernel-hardening][PATCH] arm: mm: idmap: Mark variables as ro_after

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Date:   Fri, 8 Dec 2017 12:59:22 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Jinbum Park <jinb.park7@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Russell King <linux@...linux.org.uk>,
        Greg KH <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kstewart@...uxfoundation.org, Ingo Molnar <mingo@...nel.org>,
        pombredanne@...b.com, Mark Rutland <mark.rutland@....com>
Subject: Re: [kernel-hardening][PATCH] arm: mm: idmap: Mark variables as ro_after_init

On Fri, Dec 8, 2017 at 3:13 AM, Jinbum Park <jinb.park7@...il.com> wrote:
> idmap_pgd, arch_phys_to_idmap_offset are setup once
> while init stage, and never changed after that.
> so, it is good candidate for __ro_after_init.
>
> Signed-off-by: Jinbum Park <jinb.park7@...il.com>

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

Does arm64 have anything like this? Just grepping for similar names,
idmap_t0sz looks like it could actually be const.

-Kees

> ---
>  arch/arm/mm/idmap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/mm/idmap.c b/arch/arm/mm/idmap.c
> index 10bfba8..1d1edd0 100644
> --- a/arch/arm/mm/idmap.c
> +++ b/arch/arm/mm/idmap.c
> @@ -16,8 +16,8 @@
>   * are not supported on any CPU using the idmap tables as its current
>   * page tables.
>   */
> -pgd_t *idmap_pgd;
> -long long arch_phys_to_idmap_offset;
> +pgd_t *idmap_pgd __ro_after_init;
> +long long arch_phys_to_idmap_offset __ro_after_init;
>
>  #ifdef CONFIG_ARM_LPAE
>  static void idmap_add_pmd(pud_t *pud, unsigned long addr, unsigned long end,
> --
> 1.9.1
>



-- 
Kees Cook
Pixel Security