Re: [PATCH v3 07/11] perf: Add breakpoint information to siginfo on SIGTRAP

[Peter Zijlstra]

On Wed, Mar 24, 2021 at 02:21:37PM +0100, Peter Zijlstra wrote:
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5652,13 +5652,17 @@ static long _perf_ioctl(struct perf_even
>               return perf_event_query_prog_array(event, (void __user *)arg);
>  
>       case PERF_EVENT_IOC_MODIFY_ATTRIBUTES: {
> +             struct perf_event_attr __user *uattr;
>               struct perf_event_attr new_attr;
> -             int err = perf_copy_attr((struct perf_event_attr __user *)arg,
> -                                      &new_attr);
> +             int err;
>  
> +             uattr = (struct perf_event_attr __user *)arg;
> +             err = perf_copy_attr(uattr, &new_attr);
>               if (err)
>                       return err;
>  
> +             event->siginfo.si_perf = (unsigned long)uattr;

Oh bugger; that wants updating for all children too..

> +
>               return perf_event_modify_attr(event,  &new_attr);
>       }
>       default:
> @@ -12011,6 +12010,11 @@ SYSCALL_DEFINE5(perf_event_open,
>               goto err_task;
>       }
>  
> +     clear_siginfo(&event->siginfo);
> +     event->siginfo.si_signo = SIGTRAP;
> +     event->siginfo.si_code = TRAP_PERF;
> +     event->siginfo.si_perf = (unsigned long)attr_uptr;

And inherit_event() / perf_event_alloc() want to copy/propagate that.

>       if (is_sampling_event(event)) {
>               if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
>                       err = -EOPNOTSUPP;