Re: [PATCH v2 3/5] mm: Make PR_MDWE_REFUSE_EXEC_GAIN an unsigned long

David Hildenbrand
2023-05-22T08:57:17Z

On 17.05.23 17:03, Florent Revest wrote:
> Alexey pointed out that defining a prctl flag as an int is a footgun
> because, under some circumstances, when used as a flag to prctl, it can
> be casted to long with garbage upper bits which would result in
> unexpected behaviors.
>
> This patch changes the constant to a UL to eliminate these
> possibilities.
>
> Signed-off-by: Florent Revest <revest@chromium.org>
> Suggested-by: Alexey Izbyshev <izbyshev@ispras.ru>
> ---
> include/uapi/linux/prctl.h | 2 +-
> tools/include/uapi/linux/prctl.h | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index f23d9a16507f..6e9af6cbc950 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -283,7 +283,7 @@ struct prctl_mm_map {
>
> /* Memory deny write / execute */
> #define PR_SET_MDWE 65
> -# define PR_MDWE_REFUSE_EXEC_GAIN 1
> +# define PR_MDWE_REFUSE_EXEC_GAIN (1UL << 0)
>
> #define PR_GET_MDWE 66
>
> diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h
> index 759b3f53e53f..6e6563e97fef 100644
> --- a/tools/include/uapi/linux/prctl.h
> +++ b/tools/include/uapi/linux/prctl.h
> @@ -283,7 +283,7 @@ struct prctl_mm_map {
>
> /* Memory deny write / execute */
> #define PR_SET_MDWE 65
> -# define PR_MDWE_REFUSE_EXEC_GAIN 1
> +# define PR_MDWE_REFUSE_EXEC_GAIN (1UL << 0)
>
> #define PR_GET_MDWE 66
>

Both are changing existing uapi, so you'll already have existing user
space using the old values, that your kernel code has to deal with no?

--
Thanks,

David / dhildenb