From ca3bb3d027f69ac3ab1dafb32bde2f5a3a44439c Mon Sep 17 00:00:00 2001 From: Elena Reshetova Date: Mon, 28 Jan 2019 14:27:28 +0200 Subject: [PATCH] perf/ring_buffer: Convert ring_buffer.aux_refcount to refcount_t atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable ring_buffer.aux_refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. ** Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. Please check Documentation/core-api/refcount-vs-atomic.rst for more information. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the ring_buffer.aux_refcount it might make a difference in following places: - perf_aux_output_begin(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - rb_free_aux(): decrement in refcount_dec_and_test() only provides RELEASE ordering and ACQUIRE ordering + control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook Signed-off-by: Elena Reshetova Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: acme@kernel.org Cc: namhyung@kernel.org Link: https://lkml.kernel.org/r/1548678448-24458-4-git-send-email-elena.reshetova@intel.com Signed-off-by: Ingo Molnar --- kernel/events/core.c | 2 +- kernel/events/internal.h | 2 +- kernel/events/ring_buffer.c | 6 +++--- 3 files changed, 5 insertions(+), 5 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 284232edf9be..5aeb4c74fb99 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5468,7 +5468,7 @@ static void perf_mmap_close(struct vm_area_struct *vma) /* this has to be the last one */ rb_free_aux(rb); - WARN_ON_ONCE(atomic_read(&rb->aux_refcount)); + WARN_ON_ONCE(refcount_read(&rb->aux_refcount)); mutex_unlock(&event->mmap_mutex); } diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 4718de2a04e6..79c47076700a 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -49,7 +49,7 @@ struct ring_buffer { atomic_t aux_mmap_count; unsigned long aux_mmap_locked; void (*free_aux)(void *); - atomic_t aux_refcount; + refcount_t aux_refcount; void **aux_pages; void *aux_priv; diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 0a71d16ca41b..805f0423ee0b 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -357,7 +357,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, if (!atomic_read(&rb->aux_mmap_count)) goto err; - if (!atomic_inc_not_zero(&rb->aux_refcount)) + if (!refcount_inc_not_zero(&rb->aux_refcount)) goto err; /* @@ -670,7 +670,7 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event, * we keep a refcount here to make sure either of the two can * reference them safely. */ - atomic_set(&rb->aux_refcount, 1); + refcount_set(&rb->aux_refcount, 1); rb->aux_overwrite = overwrite; rb->aux_watermark = watermark; @@ -689,7 +689,7 @@ out: void rb_free_aux(struct ring_buffer *rb) { - if (atomic_dec_and_test(&rb->aux_refcount)) + if (refcount_dec_and_test(&rb->aux_refcount)) __rb_free_aux(rb); }