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

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

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;