perf: Copy perf_event_attr::sig_data on modification

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@google.com>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Link: https://lore.kernel.org/r/20220131103407.1971678-1-elver@google.com

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 76c754e..57c7197 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3238,6 +3238,15 @@ 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)
 {
@@ -3260,10 +3269,17 @@ 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;