Hi,
On Mon, Nov 28, 2022, Sven Peter wrote:
> 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@xxxxxxxxxxxxx>
> ---
> 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
>
This looks good to me. This should also go on stable.
Acked-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
Thanks!
Thinh
