Re: [PATCH v2] usb: dwc3: gadget: Ignore dwc3 interrupt if GEVNTCOUNT reads corrupt value

[Thinh Nguyen]

On Thu, Dec 21, 2023, Krishna Kurapati wrote:
> In the current implementation, the check_event_buf call reads the
> GEVNTCOUNT register to determine the amount of event data generated
> and copies it from ev->buf to ev->cache after masking interrupt.
> 
> During copy if the amount of data to be copied is more than
> (length - lpos), we fill the ev->cache till the end of 4096 byte
> buffer allocated and then start filling from the top (lpos = 0).
> 
> In one instance of SMMU crash it is observed that GEVNTCOUNT register
> reads more than 4096 bytes:
> 
> dwc3_readl   base=0xffffffc0091dc000  offset=50188  value=63488
> 
> (offset = 50188 -> 0xC40C)  -> reads 63488 bytes
> 
> As per crash dump:
> dwc->lpos = 2056
> 
> and evt->buf is at 0xFFFFFFC009185000 and the crash is at
> 0xFFFFFFC009186000. The diff which is exactly 0x1000 bytes.
> 
> We first memcpy 2040 bytes from (buf + lpos) to (buf + 0x1000).
> 
> And then we copy the rest of the data (64388 - 2040) from beginning
> of dwc->ev_buf. While doing so we go beyond bounds as we are trying
> to memcpy 62348 bytes into a 4K buffer resulting in crash.
> 
> Fix this by ignoring the interrupt when GEVNTCOUNT register reads a
> value more than the event ring allocated.
> 
> Signed-off-by: Krishna Kurapati <quic_kriskura@xxxxxxxxxxx>
> ---
> Changes in v2:
> Instead of fixing amount of data being copied from ring, ignored
> the interrupt when count is corrupt as per suggestion from Thinh.
> 
> Link to v1:
> https://urldefense.com/v3/__https://lore.kernel.org/all/20230521100330.22478-1-quic_kriskura@xxxxxxxxxxx/__;!!A4F2R9G_pg!ewM3u9Pdk8yD9eU24sOuQqmhm8M2VpGXH8zALqVWGKffGbcJxrtyKKlUPuh8SS2arqO09DjnC9atC3bemEpx-g5UQMllbA$ 
> 
>  drivers/usb/dwc3/gadget.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 858fe4c299b7..e27933fdcce3 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -4451,6 +4451,7 @@ static irqreturn_t dwc3_thread_interrupt(int irq, void *_evt)
>  static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>  {
>  	struct dwc3 *dwc = evt->dwc;
> +	int ret = IRQ_WAKE_THREAD;

irqreturn_t instead of int?

>  	u32 amount;
>  	u32 count;
>  
> @@ -4480,6 +4481,12 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>  	if (!count)
>  		return IRQ_NONE;
>  
> +	if (count > evt->length) {
> +		dev_err(dwc->dev, "GEVTCOUNT corrupt\n");
> +		ret = IRQ_NONE;
> +		goto done;
> +	}
> +
>  	evt->count = count;
>  	evt->flags |= DWC3_EVENT_PENDING;
>  
> @@ -4493,9 +4500,10 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>  	if (amount < count)
>  		memcpy(evt->cache, evt->buf, count - amount);
>  
> +done:
>  	dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), count);

Don't update the GEVNTCOUNT if the read is invalid. We're not processing
any event, so we should not write back the "count" that we did not
process.

>  
> -	return IRQ_WAKE_THREAD;
> +	return ret;
>  }
>  
>  static irqreturn_t dwc3_interrupt(int irq, void *_evt)
> -- 
> 2.42.0
> 

Thanks,
Thinh