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

From: Kees Cook
Date: Fri Aug 12 2016 - 14:06:21 EST


On Fri, Aug 12, 2016 at 1:12 AM, Jisheng Zhang <jszhang@xxxxxxxxxxx> 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@xxxxxxxxxxx>

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

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-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