perf: Support only inheriting events if cloned with CLONE_THREAD

Adds bit perf_event_attr::inherit_thread, to restricting inheriting
events only if the child was cloned with CLONE_THREAD.

This option supports the case where an event is supposed to be
process-wide only (including subthreads), but should not propagate
beyond the current process's shared environment.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/YBvj6eJR%2FDY2TsEB@hirez.programming.kicks-ass.net/

1 files changed, 14 insertions, 7 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 10ed2cd434dc..3e3c00fd0b2e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11653,6 +11653,9 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 	    (attr->sample_type & PERF_SAMPLE_WEIGHT_STRUCT))
 		return -EINVAL;
 
+	if (!attr->inherit && attr->inherit_thread)
+		return -EINVAL;
+
 out:
 	return ret;
 
@@ -12873,12 +12876,13 @@ static int
 inherit_task_group(struct perf_event *event, struct task_struct *parent,
 		   struct perf_event_context *parent_ctx,
 		   struct task_struct *child, int ctxn,
-		   int *inherited_all)
+		   u64 clone_flags, int *inherited_all)
 {
 	int ret;
 	struct perf_event_context *child_ctx;
 
-	if (!event->attr.inherit) {
+	if (!event->attr.inherit ||
+	    (event->attr.inherit_thread && !(clone_flags & CLONE_THREAD))) {
 		*inherited_all = 0;
 		return 0;
 	}
@@ -12910,7 +12914,8 @@ inherit_task_group(struct perf_event *event, struct task_struct *parent,
 /*
  * Initialize the perf_event context in task_struct
  */
-static int perf_event_init_context(struct task_struct *child, int ctxn)
+static int perf_event_init_context(struct task_struct *child, int ctxn,
+				   u64 clone_flags)
 {
 	struct perf_event_context *child_ctx, *parent_ctx;
 	struct perf_event_context *cloned_ctx;
@@ -12950,7 +12955,8 @@ static int perf_event_init_context(struct task_struct *child, int ctxn)
 	 */
 	perf_event_groups_for_each(event, &parent_ctx->pinned_groups) {
 		ret = inherit_task_group(event, parent, parent_ctx,
-					 child, ctxn, &inherited_all);
+					 child, ctxn, clone_flags,
+					 &inherited_all);
 		if (ret)
 			goto out_unlock;
 	}
@@ -12966,7 +12972,8 @@ static int perf_event_init_context(struct task_struct *child, int ctxn)
 
 	perf_event_groups_for_each(event, &parent_ctx->flexible_groups) {
 		ret = inherit_task_group(event, parent, parent_ctx,
-					 child, ctxn, &inherited_all);
+					 child, ctxn, clone_flags,
+					 &inherited_all);
 		if (ret)
 			goto out_unlock;
 	}
@@ -13008,7 +13015,7 @@ out_unlock:
 /*
  * Initialize the perf_event context in task_struct
  */
-int perf_event_init_task(struct task_struct *child)
+int perf_event_init_task(struct task_struct *child, u64 clone_flags)
 {
 	int ctxn, ret;
 
@@ -13017,7 +13024,7 @@ int perf_event_init_task(struct task_struct *child)
 	INIT_LIST_HEAD(&child->perf_event_list);
 
 	for_each_task_context_nr(ctxn) {
-		ret = perf_event_init_context(child, ctxn);
+		ret = perf_event_init_context(child, ctxn, clone_flags);
 		if (ret) {
 			perf_event_free_task(child);
 			return ret;