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Message-ID: <20240722210648.80892-2-lucas.demarchi@intel.com>
Date: Mon, 22 Jul 2024 14:06:42 -0700
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: intel-gfx@...ts.freedesktop.org,
linux-perf-users@...r.kernel.org
Cc: Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
dri-devel@...ts.freedesktop.org,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
linux-kernel@...r.kernel.org,
Lucas De Marchi <lucas.demarchi@...el.com>
Subject: [PATCH 1/7] perf/core: Add pmu get/put
If a pmu is unregistered while there's an active event, perf will still
access the pmu via event->pmu, even after the event is destroyed. This
makes it difficult for drivers like i915 that take a reference on the
device when the event is created and put it when it's destroyed.
Currently the following use-after-free happens just after destroying the
event:
BUG: KASAN: use-after-free in exclusive_event_destroy+0xd8/0xf0
Read of size 4 at addr ffff88816e2bb63c by task perf/7748
Whenever and event is created, get a pmu reference to use in event->pmu
and just before calling module_put(), drop the reference..
Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
---
include/linux/perf_event.h | 3 +++
kernel/events/core.c | 32 ++++++++++++++++++++++++++++----
2 files changed, 31 insertions(+), 4 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index a5304ae8c654..7048a505e93c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -540,6 +540,9 @@ struct pmu {
* Check period value for PERF_EVENT_IOC_PERIOD ioctl.
*/
int (*check_period) (struct perf_event *event, u64 value); /* optional */
+
+ struct pmu *(*get) (struct pmu *pmu); /* optional: get a reference */
+ void (*put) (struct pmu *pmu); /* optional: put a reference */
};
enum perf_addr_filter_action_t {
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1b6f5dc7ed32..cc7541b644b0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5208,6 +5208,8 @@ static void perf_addr_filters_splice(struct perf_event *event,
static void _free_event(struct perf_event *event)
{
+ struct module *module;
+
irq_work_sync(&event->pending_irq);
unaccount_event(event);
@@ -5259,7 +5261,13 @@ static void _free_event(struct perf_event *event)
put_ctx(event->ctx);
exclusive_event_destroy(event);
- module_put(event->pmu->module);
+
+ module = event->pmu->module;
+ event->pmu->put(event->pmu);
+ /* can't touch pmu anymore */
+ event->pmu = NULL;
+
+ module_put(module);
call_rcu(&event->rcu_head, free_event_rcu);
}
@@ -11331,6 +11339,11 @@ static int perf_pmu_nop_int(struct pmu *pmu)
return 0;
}
+static struct pmu *perf_pmu_nop_pmu(struct pmu *pmu)
+{
+ return pmu;
+}
+
static int perf_event_nop_int(struct perf_event *event, u64 value)
{
return 0;
@@ -11617,6 +11630,12 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
if (!pmu->event_idx)
pmu->event_idx = perf_event_idx_default;
+ if (!pmu->get)
+ pmu->get = perf_pmu_nop_pmu;
+
+ if (!pmu->put)
+ pmu->put = perf_pmu_nop_void;
+
list_add_rcu(&pmu->entry, &pmus);
atomic_set(&pmu->exclusive_cnt, 0);
ret = 0;
@@ -11695,7 +11714,8 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
BUG_ON(!ctx);
}
- event->pmu = pmu;
+ event->pmu = pmu->get(pmu);
+
ret = pmu->event_init(event);
if (ctx)
@@ -11714,8 +11734,12 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
event->destroy(event);
}
- if (ret)
- module_put(pmu->module);
+ if (ret) {
+ struct module *module = pmu->module;
+
+ pmu->put(pmu);
+ module_put(module);
+ }
return ret;
}
--
2.43.0
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