Re: [PATCH v2] usb: dwc3: core: Prevent USB core invalid event buffer address access

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

On 8/14/2024 4:47 AM, Thinh Nguyen wrote:
> On Sat, Aug 10, 2024, Selvarasu Ganesan wrote:
>> On 8/10/2024 4:58 AM, Thinh Nguyen wrote:
>>> On Thu, Aug 08, 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
>>> This is a workaround to your specific setup behavior. Please document in
>>> the commit message which platforms are impacted.
>> Please correct me if i am wrong. I dont think this workaround only
>> applicable our specific setup. It could be a common issue across all
>> other vendor platforms, and it's required to must check the controller
>> status before clear the event buffers address.  What you think is it
>> really required to mention the platform details in commit message?
> How can it be a common issue, the suspend sequence hasn't completed in
> the dwc3 driver but yet the buffer is no longer accessible? Also, as you
> noted, we don't know the exact condition for the SMMU fault, and this
> isn't reproducible all the time.

Agree. Will update platform detail in next version.
>
>>>>           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.
>>>>
>>>> Cc: stable@vger.kernel.org
>>> We can keep the stable tag, but there's no issue with the commit below.
>>
>> By mistaken I mentioned wrong commit ID. The correct commit id would be
>> 660e9bde74d69 ("usb: dwc3: remove num_event_buffers").
> The above commit isn't the issue either. If it is, then the problem
> should still exist prior to that.


This issue still persists in older kernels (6.1.X) as well. We believed 
that it could be a common issue due to the missing condition for 
checking the controller status in the mentioned commit above. We require 
this fix in all stable kernel for the Exynos platform. Is it fine to 
only mention the "Cc" tag in this case?
>
>>>> Fixes: 89d7f9629946 ("usb: dwc3: core: Skip setting event buffers for host only controllers")
>>>> Signed-off-by: Selvarasu Ganesan <selvarasu.g@samsung.com>
>>>> ---
>>>>
>>>> Changes in v2:
>>>> - Added separate check for USB controller status before cleaning the
>>>>     event buffer.
>>>> - Link to v1: https://urldefense.com/v3/__https://lore.kernel.org/lkml/20240722145617.537-1-selvarasu.g@samsung.com/__;!!A4F2R9G_pg!cvZmnaxTWtJKR4ZDRZDa-8mvxpvkf5KPx57IwSXTSEtEFIVkPullR7sTYP0AM9de0xFbHLKdM_5jzBUiBL3f9SuioYE$
>>>> ---
>>>>    drivers/usb/dwc3/core.c | 5 +++++
>>>>    1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>>>> index 734de2a8bd21..5b67d9bca71b 100644
>>>> --- a/drivers/usb/dwc3/core.c
>>>> +++ b/drivers/usb/dwc3/core.c
>>>> @@ -564,10 +564,15 @@ 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)
>>>>    		return;
>>>>    
>>> Please add comment here why we need this and which platform is impacted
>>> should we need to go back and test.
>> Do you want add comment as like below?. If yes, As i said earlier not
>> required to mention our platform name as it could be a common issue
>> across all the other vendor platforms.
> See note above.

Noted.
>
>> /*Prevent USB controller invalid event buffer address access
>> in Exynos platform if USB controller still in active.*/
> Perhaps this:
>
> /*
>   * Exynos platforms may not be able to access event buffer if the
>   * controller failed to halt on dwc3_core_exit().

Thanks for the suggestions. Will update platform detail in next version.
>   */
>
>   BR,
>   Thinh
>
>>>> +	reg = dwc3_readl(dwc->regs, DWC3_DSTS);
>>>> +	if (!(reg & DWC3_DSTS_DEVCTRLHLT))
>>>> +		return;
>>>> +
>>>>    	evt = dwc->ev_buf;
>>>>    
>>>>    	evt->lpos = 0;
>>>> -- 
>>>> 2.17.1
>>>>
>>> Thanks,
>>> Thinh