crypto: qat - flush misc workqueue during device shutdown

Repeated loading and unloading of a device specific QAT driver, for
example qat_4xxx, in a tight loop can lead to a crash due to a
use-after-free scenario. This occurs when a power management (PM)
interrupt triggers just before the device-specific driver (e.g.,
qat_4xxx.ko) is unloaded, while the core driver (intel_qat.ko) remains
loaded.

Since the driver uses a shared workqueue (`qat_misc_wq`) across all
devices and owned by intel_qat.ko, a deferred routine from the
device-specific driver may still be pending in the queue. If this
routine executes after the driver is unloaded, it can dereference freed
memory, resulting in a page fault and kernel crash like the following:

    BUG: unable to handle page fault for address: ffa000002e50a01c
    #PF: supervisor read access in kernel mode
    RIP: 0010:pm_bh_handler+0x1d2/0x250 [intel_qat]
    Call Trace:
      pm_bh_handler+0x1d2/0x250 [intel_qat]
      process_one_work+0x171/0x340
      worker_thread+0x277/0x3a0
      kthread+0xf0/0x120
      ret_from_fork+0x2d/0x50

To prevent this, flush the misc workqueue during device shutdown to
ensure that all pending work items are completed before the driver is
unloaded.

Note: This approach may slightly increase shutdown latency if the
workqueue contains jobs from other devices, but it ensures correctness
and stability.

Fixes: e5745f3 ("crypto: qat - enable power management for QAT GEN4")
Signed-off-by: Giovanni Cabiddu <[email protected]>
Cc: [email protected]
Reviewed-by: Ahsan Atta <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>

Author: gcabiddu

drivers/crypto/intel/qat/qat_common/adf_common_drv.h

@@ -189,6 +189,7 @@ void adf_exit_misc_wq(void);
 bool adf_misc_wq_queue_work(struct work_struct *work);
 bool adf_misc_wq_queue_delayed_work(struct delayed_work *work,
 				    unsigned long delay);
+void adf_misc_wq_flush(void);
 #if defined(CONFIG_PCI_IOV)
 int adf_sriov_configure(struct pci_dev *pdev, int numvfs);
 void adf_disable_sriov(struct adf_accel_dev *accel_dev);

drivers/crypto/intel/qat/qat_common/adf_init.c

@@ -404,6 +404,7 @@ static void adf_dev_shutdown(struct adf_accel_dev *accel_dev)
 		hw_data->exit_admin_comms(accel_dev);
 
 	adf_cleanup_etr_data(accel_dev);
+	adf_misc_wq_flush();
 	adf_dev_restore(accel_dev);
 }
 

drivers/crypto/intel/qat/qat_common/adf_isr.c

@@ -407,3 +407,8 @@ bool adf_misc_wq_queue_delayed_work(struct delayed_work *work,
 {
 	return queue_delayed_work(adf_misc_wq, work, delay);
 }
+
+void adf_misc_wq_flush(void)
+{
+	flush_workqueue(adf_misc_wq);
+}