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authorPeter Zijlstra <peterz@infradead.org>2023-10-18 14:56:54 +0300
committerPeter Zijlstra <peterz@infradead.org>2023-10-19 11:09:42 +0300
commit32671e3799ca2e4590773fd0e63aaa4229e50c06 (patch)
tree2e0c436e51dafdf7a4ea71dcbf7e716ef203d8c5 /kernel
parent58720809f52779dc0f08e53e54b014209d13eebb (diff)
downloadlinux-32671e3799ca2e4590773fd0e63aaa4229e50c06.tar.xz
perf: Disallow mis-matched inherited group reads
Because group consistency is non-atomic between parent (filedesc) and children (inherited) events, it is possible for PERF_FORMAT_GROUP read() to try and sum non-matching counter groups -- with non-sensical results. Add group_generation to distinguish the case where a parent group removes and adds an event and thus has the same number, but a different configuration of events as inherited groups. This became a problem when commit fa8c269353d5 ("perf/core: Invert perf_read_group() loops") flipped the order of child_list and sibling_list. Previously it would iterate the group (sibling_list) first, and for each sibling traverse the child_list. In this order, only the group composition of the parent is relevant. By flipping the order the group composition of the child (inherited) events becomes an issue and the mis-match in group composition becomes evident. That said; even prior to this commit, while reading of a group that is not equally inherited was not broken, it still made no sense. (Ab)use ECHILD as error return to indicate issues with child process group composition. Fixes: fa8c269353d5 ("perf/core: Invert perf_read_group() loops") Reported-by: Budimir Markovic <markovicbudimir@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20231018115654.GK33217@noisy.programming.kicks-ass.net
Diffstat (limited to 'kernel')
-rw-r--r--kernel/events/core.c39
1 files changed, 33 insertions, 6 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4c72a41f11af..d0663b9324e7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1954,6 +1954,7 @@ static void perf_group_attach(struct perf_event *event)
list_add_tail(&event->sibling_list, &group_leader->sibling_list);
group_leader->nr_siblings++;
+ group_leader->group_generation++;
perf_event__header_size(group_leader);
@@ -2144,6 +2145,7 @@ static void perf_group_detach(struct perf_event *event)
if (leader != event) {
list_del_init(&event->sibling_list);
event->group_leader->nr_siblings--;
+ event->group_leader->group_generation++;
goto out;
}
@@ -5440,7 +5442,7 @@ static int __perf_read_group_add(struct perf_event *leader,
u64 read_format, u64 *values)
{
struct perf_event_context *ctx = leader->ctx;
- struct perf_event *sub;
+ struct perf_event *sub, *parent;
unsigned long flags;
int n = 1; /* skip @nr */
int ret;
@@ -5450,6 +5452,33 @@ static int __perf_read_group_add(struct perf_event *leader,
return ret;
raw_spin_lock_irqsave(&ctx->lock, flags);
+ /*
+ * Verify the grouping between the parent and child (inherited)
+ * events is still in tact.
+ *
+ * Specifically:
+ * - leader->ctx->lock pins leader->sibling_list
+ * - parent->child_mutex pins parent->child_list
+ * - parent->ctx->mutex pins parent->sibling_list
+ *
+ * Because parent->ctx != leader->ctx (and child_list nests inside
+ * ctx->mutex), group destruction is not atomic between children, also
+ * see perf_event_release_kernel(). Additionally, parent can grow the
+ * group.
+ *
+ * Therefore it is possible to have parent and child groups in a
+ * different configuration and summing over such a beast makes no sense
+ * what so ever.
+ *
+ * Reject this.
+ */
+ parent = leader->parent;
+ if (parent &&
+ (parent->group_generation != leader->group_generation ||
+ parent->nr_siblings != leader->nr_siblings)) {
+ ret = -ECHILD;
+ goto unlock;
+ }
/*
* Since we co-schedule groups, {enabled,running} times of siblings
@@ -5483,8 +5512,9 @@ static int __perf_read_group_add(struct perf_event *leader,
values[n++] = atomic64_read(&sub->lost_samples);
}
+unlock:
raw_spin_unlock_irqrestore(&ctx->lock, flags);
- return 0;
+ return ret;
}
static int perf_read_group(struct perf_event *event,
@@ -5503,10 +5533,6 @@ static int perf_read_group(struct perf_event *event,
values[0] = 1 + leader->nr_siblings;
- /*
- * By locking the child_mutex of the leader we effectively
- * lock the child list of all siblings.. XXX explain how.
- */
mutex_lock(&leader->child_mutex);
ret = __perf_read_group_add(leader, read_format, values);
@@ -13346,6 +13372,7 @@ static int inherit_group(struct perf_event *parent_event,
!perf_get_aux_event(child_ctr, leader))
return -EINVAL;
}
+ leader->group_generation = parent_event->group_generation;
return 0;
}