On Wed, Mar 24, 2021 at 01:53:48PM +0100, Peter Zijlstra wrote:
> On Wed, Mar 24, 2021 at 12:24:59PM +0100, Marco Elver wrote:
> > Encode information from breakpoint attributes into siginfo_t, which
> > helps disambiguate which breakpoint fired.
> >
> > Note, providing the event fd may be unreliable, since the event may have
> > been modified (via PERF_EVENT_IOC_MODIFY_ATTRIBUTES) between the event
> > triggering and the signal being delivered to user space.
> >
> > Signed-off-by: Marco Elver <el...@google.com>
> > ---
> > v2:
> > * Add comment about si_perf==0.
> > ---
> > kernel/events/core.c | 16 ++++++++++++++++
> > 1 file changed, 16 insertions(+)
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 1e4c949bf75f..0316d39e8c8f 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -6399,6 +6399,22 @@ static void perf_sigtrap(struct perf_event *event)
> > info.si_signo = SIGTRAP;
> > info.si_code = TRAP_PERF;
> > info.si_errno = event->attr.type;
> > +
> > + switch (event->attr.type) {
> > + case PERF_TYPE_BREAKPOINT:
> > + info.si_addr = (void *)(unsigned long)event->attr.bp_addr;
> > + info.si_perf = (event->attr.bp_len << 16) |
> > (u64)event->attr.bp_type;
>
> Ahh, here's the si_perf user. I wasn't really clear to me what was
> supposed to be in that field at patch #5 where it was introduced.
>
> Would it perhaps make sense to put the user address of struct
> perf_event_attr in there instead? (Obviously we'd have to carry it from
> the syscall to here, but it might be more useful than a random encoding
> of some bits therefrom).
>
> Then we can also clearly document that's in that field, and it might be
> more useful for possible other uses.
Something like so...
---
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -778,6 +778,8 @@ struct perf_event {
void *security;
#endif
struct list_head sb_list;
+
+ struct perf_event_attr __user *uattr;
#endif /* CONFIG_PERF_EVENTS */
};
--- 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->uattr = uattr;
+
return perf_event_modify_attr(event, &new_attr);
}
default:
@@ -6400,6 +6404,8 @@ static void perf_sigtrap(struct perf_eve
info.si_signo = SIGTRAP;
info.si_code = TRAP_PERF;
info.si_errno = event->attr.type;
+ info.si_perf = (unsigned long)event->uattr;
+
force_sig_info(&info);
}
@@ -12011,6 +12017,8 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_task;
}
+ event->uattr = attr_uptr;
+
if (is_sampling_event(event)) {
if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
err = -EOPNOTSUPP;
