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Subject[PATCH 1/3] perf: Copy perf_event_attr::sig_data on modification
From
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>
---
kernel/events/core.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fc18664f49b0..db0d85a85f1b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3197,6 +3197,15 @@ 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)
{
@@ -3219,10 +3228,17 @@ 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;
--
2.35.0.rc2.247.g8bbb082509-goog
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