linux-kernel - Re: [PATCH v3] ARM: VDSO: put RO and RO after init objects into proper sections

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Date:	Fri, 12 Aug 2016 11:06:14 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	Russell King <linux@...linux.org.uk>,
	Nathan Lynch <nathan_lynch@...tor.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] ARM: VDSO: put RO and RO after init objects into
 proper sections

On Fri, Aug 12, 2016 at 1:12 AM, Jisheng Zhang <jszhang@...vell.com> wrote:
> vdso_data_mapping is never modified, so mark it as const.
>
> vdso_total_pages, vdso_data_page, vdso_text_mapping and cntvct_ok are
> initialized by vdso_init(), thereafter are read only.
>
> The fact that they are read only after init makes them candidates for
> __ro_after_init declarations.
>
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>

Looks great; thanks for keeping __ro_after_init in mind. :)

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

-Kees

> ---
>
> Since v2:
>   - include <linux/cache.h> explicitly for __ro_after_init
>
> Since v1:
>   - use __ro_after_init instead of __read_mostly
>   - apply __ro_after_init for vdso_total_pages and cntvct_ok as well
>
>  arch/arm/kernel/vdso.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c
> index 994e971..bbbffe94 100644
> --- a/arch/arm/kernel/vdso.c
> +++ b/arch/arm/kernel/vdso.c
> @@ -17,6 +17,7 @@
>   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>   */
>
> +#include <linux/cache.h>
>  #include <linux/elf.h>
>  #include <linux/err.h>
>  #include <linux/kernel.h>
> @@ -39,7 +40,7 @@
>  static struct page **vdso_text_pagelist;
>
>  /* Total number of pages needed for the data and text portions of the VDSO. */
> -unsigned int vdso_total_pages __read_mostly;
> +unsigned int vdso_total_pages __ro_after_init;
>
>  /*
>   * The VDSO data page.
> @@ -47,13 +48,13 @@ unsigned int vdso_total_pages __read_mostly;
>  static union vdso_data_store vdso_data_store __page_aligned_data;
>  static struct vdso_data *vdso_data = &vdso_data_store.data;
>
> -static struct page *vdso_data_page;
> -static struct vm_special_mapping vdso_data_mapping = {
> +static struct page *vdso_data_page __ro_after_init;
> +static const struct vm_special_mapping vdso_data_mapping = {
>         .name = "[vvar]",
>         .pages = &vdso_data_page,
>  };
>
> -static struct vm_special_mapping vdso_text_mapping = {
> +static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
>         .name = "[vdso]",
>  };
>
> @@ -67,7 +68,7 @@ struct elfinfo {
>  /* Cached result of boot-time check for whether the arch timer exists,
>   * and if so, whether the virtual counter is useable.
>   */
> -static bool cntvct_ok __read_mostly;
> +static bool cntvct_ok __ro_after_init;
>
>  static bool __init cntvct_functional(void)
>  {
> --
> 2.8.1
>



-- 
Kees Cook
Nexus Security