On Wed, Mar 24, 2021 at 02:01:56PM +0100, Peter Zijlstra wrote:
> 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...
Ok possibly something like so, which also gets the data address right
for more cases.
---
--- 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 kernel_siginfo siginfo;
#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->siginfo.si_perf = (unsigned long)uattr;
+
return perf_event_modify_attr(event, &new_attr);
}
default:
@@ -6394,13 +6398,7 @@ void perf_event_wakeup(struct perf_event
static void perf_sigtrap(struct perf_event *event)
{
- struct kernel_siginfo info;
-
- clear_siginfo(&info);
- info.si_signo = SIGTRAP;
- info.si_code = TRAP_PERF;
- info.si_errno = event->attr.type;
- force_sig_info(&info);
+ force_sig_info(&event->siginfo);
}
static void perf_pending_event_disable(struct perf_event *event)
@@ -6414,8 +6412,8 @@ static void perf_pending_event_disable(s
WRITE_ONCE(event->pending_disable, -1);
if (event->attr.sigtrap) {
- atomic_set(&event->event_limit, 1); /* rearm event */
perf_sigtrap(event);
+ atomic_set_release(&event->event_limit, 1); /* rearm
event */
return;
}
@@ -9121,6 +9119,7 @@ static int __perf_event_overflow(struct
if (events && atomic_dec_and_test(&event->event_limit)) {
ret = 1;
event->pending_kill = POLL_HUP;
+ event->siginfo.si_addr = (void *)data->addr;
perf_event_disable_inatomic(event);
}
@@ -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;
+
if (is_sampling_event(event)) {
if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
err = -EOPNOTSUPP;
