Re: [PATCH 1/3] perf: Copy perf_event_attr::sig_data on modification

[Dmitry Vyukov]

On Mon, 31 Jan 2022 at 11:34, Marco Elver <elver@xxxxxxxxxx> wrote:
>
> The intent has always been that perf_event_attr::sig_data should also be
> modifiable along with PERF_EVENT_IOC_MODIFY_ATTRIBUTES, because it is
> observable by user space if SIGTRAP on events is requested.
>
> Currently only PERF_TYPE_BREAKPOINT is modifiable, and explicitly copies
> relevant breakpoint-related attributes in hw_breakpoint_copy_attr().
> This misses copying perf_event_attr::sig_data.
>
> Since sig_data is not specific to PERF_TYPE_BREAKPOINT, introduce a
> helper to copy generic event-type-independent attributes on
> modification.
>
> Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events")
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>

Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

Thanks for the quick fix.

> ---
>  kernel/events/core.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index fc18664f49b0..db0d85a85f1b 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3197,6 +3197,15 @@ static int perf_event_modify_breakpoint(struct perf_event *bp,
>         return err;
>  }
>
> +/*
> + * Copy event-type-independent attributes that may be modified.
> + */
> +static void perf_event_modify_copy_attr(struct perf_event_attr *to,
> +                                       const struct perf_event_attr *from)
> +{
> +       to->sig_data = from->sig_data;
> +}
> +
>  static int perf_event_modify_attr(struct perf_event *event,
>                                   struct perf_event_attr *attr)
>  {
> @@ -3219,10 +3228,17 @@ static int perf_event_modify_attr(struct perf_event *event,
>         WARN_ON_ONCE(event->ctx->parent_ctx);
>
>         mutex_lock(&event->child_mutex);
> +       /*
> +        * Event-type-independent attributes must be copied before event-type
> +        * modification, which will validate that final attributes match the
> +        * source attributes after all relevant attributes have been copied.
> +        */
> +       perf_event_modify_copy_attr(&event->attr, attr);
>         err = func(event, attr);
>         if (err)
>                 goto out;
>         list_for_each_entry(child, &event->child_list, child_list) {
> +               perf_event_modify_copy_attr(&child->attr, attr);
>                 err = func(child, attr);
>                 if (err)
>                         goto out;
> --
> 2.35.0.rc2.247.g8bbb082509-goog
>