| Message ID | YnKWuLQZdPwSdRTh@linutronix.de |
|---|---|
| State | Accepted |
| Commit | 91e8bcd7b4da182e09ea19a2c73167345fe14c98 |
| Headers | show |
| Series | crypto: cryptd - Protect per-CPU resource by disabling BH. | expand |
On Wed, May 04, 2022 at 05:07:36PM +0200, Sebastian Andrzej Siewior wrote: > The access to cryptd_queue::cpu_queue is synchronized by disabling > preemption in cryptd_enqueue_request() and disabling BH in > cryptd_queue_worker(). This implies that access is allowed from BH. > > If cryptd_enqueue_request() is invoked from preemptible context _and_ > soft interrupt then this can lead to list corruption since > cryptd_enqueue_request() is not protected against access from > soft interrupt. > > Replace get_cpu() in cryptd_enqueue_request() with local_bh_disable() > to ensure BH is always disabled. > Remove preempt_disable() from cryptd_queue_worker() since it is not > needed because local_bh_disable() ensures synchronisation. > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > --- > crypto/cryptd.c | 23 +++++++++++------------ > 1 file changed, 11 insertions(+), 12 deletions(-) Good catch! This bug has been around for a while. Did you detect this in the field or was it through code-review? Patch applied. Thanks.
On 2022-05-13 17:35:31 [+0800], Herbert Xu wrote: > > Good catch! This bug has been around for a while. Did you detect > this in the field or was it through code-review? It caused warnings in RT and we had a RT specific workaround for quite some time. Now that we try to get RT upstream I've been looking how to solve this differently and came up with this. > Patch applied. Thanks. Thank you. Sebastian
diff --git a/crypto/cryptd.c b/crypto/cryptd.c index a1bea0f4baa88..668095eca0faf 100644 --- a/crypto/cryptd.c +++ b/crypto/cryptd.c @@ -39,6 +39,10 @@ struct cryptd_cpu_queue { }; struct cryptd_queue { + /* + * Protected by disabling BH to allow enqueueing from softinterrupt and + * dequeuing from kworker (cryptd_queue_worker()). + */ struct cryptd_cpu_queue __percpu *cpu_queue; }; @@ -125,28 +129,28 @@ static void cryptd_fini_queue(struct cryptd_queue *queue) static int cryptd_enqueue_request(struct cryptd_queue *queue, struct crypto_async_request *request) { - int cpu, err; + int err; struct cryptd_cpu_queue *cpu_queue; refcount_t *refcnt; - cpu = get_cpu(); + local_bh_disable(); cpu_queue = this_cpu_ptr(queue->cpu_queue); err = crypto_enqueue_request(&cpu_queue->queue, request); refcnt = crypto_tfm_ctx(request->tfm); if (err == -ENOSPC) - goto out_put_cpu; + goto out; - queue_work_on(cpu, cryptd_wq, &cpu_queue->work); + queue_work_on(smp_processor_id(), cryptd_wq, &cpu_queue->work); if (!refcount_read(refcnt)) - goto out_put_cpu; + goto out; refcount_inc(refcnt); -out_put_cpu: - put_cpu(); +out: + local_bh_enable(); return err; } @@ -162,15 +166,10 @@ static void cryptd_queue_worker(struct work_struct *work) cpu_queue = container_of(work, struct cryptd_cpu_queue, work); /* * Only handle one request at a time to avoid hogging crypto workqueue. - * preempt_disable/enable is used to prevent being preempted by - * cryptd_enqueue_request(). local_bh_disable/enable is used to prevent - * cryptd_enqueue_request() being accessed from software interrupts. */ local_bh_disable(); - preempt_disable(); backlog = crypto_get_backlog(&cpu_queue->queue); req = crypto_dequeue_request(&cpu_queue->queue); - preempt_enable(); local_bh_enable(); if (!req)
The access to cryptd_queue::cpu_queue is synchronized by disabling preemption in cryptd_enqueue_request() and disabling BH in cryptd_queue_worker(). This implies that access is allowed from BH. If cryptd_enqueue_request() is invoked from preemptible context _and_ soft interrupt then this can lead to list corruption since cryptd_enqueue_request() is not protected against access from soft interrupt. Replace get_cpu() in cryptd_enqueue_request() with local_bh_disable() to ensure BH is always disabled. Remove preempt_disable() from cryptd_queue_worker() since it is not needed because local_bh_disable() ensures synchronisation. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- crypto/cryptd.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-)