[PATCH] usb: dwc3: Fix race between dwc3_set_mode and __dwc3_set_mode

[Sven Peter <sven@svenpeter.dev>]

dwc->desired_dr_role is changed by dwc3_set_mode inside a spinlock but
then read by __dwc3_set_mode outside of that lock. This can lead to a
race condition when very quick successive role switch events happen:

CPU A
	dwc3_set_mode(DWC3_GCTL_PRTCAP_HOST) // first role switch event
		spin_lock_irqsave(&dwc->lock, flags);
		dwc->desired_dr_role = mode; // DWC3_GCTL_PRTCAP_HOST
		spin_unlock_irqrestore(&dwc->lock, flags);
		queue_work(system_freezable_wq, &dwc->drd_work);

CPU B
	__dwc3_set_mode
		// ....
		spin_lock_irqsave(&dwc->lock, flags);
		// desired_dr_role is DWC3_GCTL_PRTCAP_HOST
		dwc3_set_prtcap(dwc, dwc->desired_dr_role);
		spin_unlock_irqrestore(&dwc->lock, flags);

CPU A
	dwc3_set_mode(DWC3_GCTL_PRTCAP_DEVICE) // second event
		spin_lock_irqsave(&dwc->lock, flags);
		dwc->desired_dr_role = mode; // DWC3_GCTL_PRTCAP_DEVICE
		spin_unlock_irqrestore(&dwc->lock, flags);

CPU B (continues running __dwc3_set_mode)
	switch (dwc->desired_dr_role) { // DWC3_GCTL_PRTCAP_DEVICE
	// ....
	case DWC3_GCTL_PRTCAP_DEVICE:
		// ....
		ret = dwc3_gadget_init(dwc);

We then have DWC3_GCTL.DWC3_GCTL_PRTCAPDIR = DWC3_GCTL_PRTCAP_HOST and
dwc->current_dr_role = DWC3_GCTL_PRTCAP_HOST but initialized the
controller in device mode. It's also possible to get into a state
where both host and device are intialized at the same time.
Fix this race by creating a local copy of desired_dr_role inside
__dwc3_set_mode while holding dwc->lock.

Fixes: 41ce1456e1db ("usb: dwc3: core: make dwc3_set_mode() work properly")
Signed-off-by: Sven Peter <sven@svenpeter.dev>
---
 drivers/usb/dwc3/core.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 1f348bc867c2..fc38a8b13efa 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -122,21 +122,25 @@ static void __dwc3_set_mode(struct work_struct *work)
 	unsigned long flags;
 	int ret;
 	u32 reg;
+	u32 desired_dr_role;
 
 	mutex_lock(&dwc->mutex);
+	spin_lock_irqsave(&dwc->lock, flags);
+	desired_dr_role = dwc->desired_dr_role;
+	spin_unlock_irqrestore(&dwc->lock, flags);
 
 	pm_runtime_get_sync(dwc->dev);
 
 	if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_OTG)
 		dwc3_otg_update(dwc, 0);
 
-	if (!dwc->desired_dr_role)
+	if (!desired_dr_role)
 		goto out;
 
-	if (dwc->desired_dr_role == dwc->current_dr_role)
+	if (desired_dr_role == dwc->current_dr_role)
 		goto out;
 
-	if (dwc->desired_dr_role == DWC3_GCTL_PRTCAP_OTG && dwc->edev)
+	if (desired_dr_role == DWC3_GCTL_PRTCAP_OTG && dwc->edev)
 		goto out;
 
 	switch (dwc->current_dr_role) {
@@ -164,7 +168,7 @@ static void __dwc3_set_mode(struct work_struct *work)
 	 */
 	if (dwc->current_dr_role && ((DWC3_IP_IS(DWC3) ||
 			DWC3_VER_IS_PRIOR(DWC31, 190A)) &&
-			dwc->desired_dr_role != DWC3_GCTL_PRTCAP_OTG)) {
+			desired_dr_role != DWC3_GCTL_PRTCAP_OTG)) {
 		reg = dwc3_readl(dwc->regs, DWC3_GCTL);
 		reg |= DWC3_GCTL_CORESOFTRESET;
 		dwc3_writel(dwc->regs, DWC3_GCTL, reg);
@@ -184,11 +188,11 @@ static void __dwc3_set_mode(struct work_struct *work)
 
 	spin_lock_irqsave(&dwc->lock, flags);
 
-	dwc3_set_prtcap(dwc, dwc->desired_dr_role);
+	dwc3_set_prtcap(dwc, desired_dr_role);
 
 	spin_unlock_irqrestore(&dwc->lock, flags);
 
-	switch (dwc->desired_dr_role) {
+	switch (desired_dr_role) {
 	case DWC3_GCTL_PRTCAP_HOST:
 		ret = dwc3_host_init(dwc);
 		if (ret) {
-- 
2.25.1