Re: [PATCH] usb: dwc3: core: Prevent USB core invalid event buffer address access

[Selvarasu Ganesan <selvarasu.g@samsung.com>]

On 8/8/2024 5:51 AM, Thinh Nguyen wrote:
> On Wed, Aug 07, 2024, Selvarasu Ganesan wrote:
>> On 8/7/2024 5:44 AM, Thinh Nguyen wrote:
>>> On Mon, Jul 22, 2024, Selvarasu Ganesan wrote:
>>>> This commit addresses an issue where the USB core could access an
>>>> invalid event buffer address during runtime suspend, potentially causing
>>>> SMMU faults and other memory issues. The problem arises from the
>>>> following sequence.
>>>> 	1. In dwc3_gadget_suspend, there is a chance of a timeout when
>>>> 	moving the USB core to the halt state after clearing the
>>>> 	run/stop bit by software.
>>>> 	2. In dwc3_core_exit, the event buffer is cleared regardless of
>>>> 	the USB core's status, which may lead to an SMMU faults and
>>>> 	other memory issues. if the USB core tries to access the event
>>>> 	buffer address.
>>>>
>>>> To prevent this issue, this commit ensures that the event buffer address
>>>> is not cleared by software  when the USB core is active during runtime
>>>> suspend by checking its status before clearing the buffer address.
>>> What happen after adding this check? Can the device resume and function
>>> properly afterward? If not, do you know if a soft-reset will recover the
>>> issue?
>>>
>>> Thanks,
>>> Thinh
>> Yes, we can see the proper resume with this fix even if the USB IP core
>> not entered into halted during suspend.
>>
>> And we not tried soft reset as this fix is working fine.
>>
>> Anyway soft reset is part of resume sequence and it will reset or
>> recover the USB IP state machine.
>>
> Ok.
>
> Just wonder, what condition does the buffer access become invalid?

Its very hard to conclude the condition here as this issue is happening 
in some random scenario when do connect/disconnect USB cable 
continuously to Host PC with some time interval by using test scripts.

> While it makes sense that we should not cleanup the buffer while the
> controller is in run state, I don't think SMMU fault will always occur
> when (!(reg & DWC3_DSTS_DEVCTRLHLT)) right?

Yes are correct. We are not always getting SMMU fault.
>
>> Thanks,
>>
>> Selva
>>
>>>> Signed-off-by: Selvarasu Ganesan <selvarasu.g@samsung.com>
>>>> ---
>>>>    drivers/usb/dwc3/core.c | 4 +++-
>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>>>> index cb82557678dd..c7c1a253862e 100644
>>>> --- a/drivers/usb/dwc3/core.c
>>>> +++ b/drivers/usb/dwc3/core.c
>>>> @@ -559,8 +559,10 @@ int dwc3_event_buffers_setup(struct dwc3 *dwc)
>>>>    void dwc3_event_buffers_cleanup(struct dwc3 *dwc)
>>>>    {
>>>>    	struct dwc3_event_buffer	*evt;
>>>> +	u32				reg;
>>>>    
>>>> -	if (!dwc->ev_buf)
>>>> +	reg = dwc3_readl(dwc->regs, DWC3_DSTS);
>>>> +	if (!dwc->ev_buf || !(reg & DWC3_DSTS_DEVCTRLHLT))
>>>>    		return;
> Can you separate the checks so we don't have to read register for all
> conditions?


Sure, will update in next version.

>
> if (!dwc->ev_buf)
> 	return;
>
> /*
>   * If dwc3_core_exit() fails, event buffer is not
>   * accessible for <XYZ> platforms.
>   */
> reg = dwc3_readl(dwc->regs, DWC3_DSTS);
> if (!(reg & DWC3_DSTS_DEVCTRLHLT))
> 	return;
>
> Thanks,
> Thinh
>
>>>>    
>>>>    	evt = dwc->ev_buf;
>>>> -- 
>>>> 2.17.1