Re: Highly critical bug in XHCI Controller

["Michał Pecio" <michal.pecio@gmail.com>]

Hi,

> Basically the issue comes from hub_port_connect.
> 
> drivers/usb/core/hub.c
> 
> hub_port_init returns -71 -EPROTO and jumps to loop
> https://github.com/torvalds/linux/blob/master/drivers/usb/core/hub.c#L5450
> 
> I'd question if usb_ep0_reinit is really required in loop which is
> running following functions:
>     usb_disable_endpoint(udev, 0 + USB_DIR_IN, true);
>     usb_disable_endpoint(udev, 0 + USB_DIR_OUT, true);
>     usb_enable_endpoint(udev, &udev->ep0, true);
> 
> this is something only experience over the past decades can tell?
> 
> usb_enable_endpoint will trigger xhci_endpoint_reset which doesn't do
> much, but crashes the entire system with the upstream kernel when it
> triggers xhci_check_bw_table).
> 
> I removed usb_ep0_reinit here and devices are still workable under
> various conditions (again I shorted and pulled D+/D- to ground for
> testing).

xHCI isn't the only host controller supported by Linux, and
usb_ep0_reinit() predates it. Maybe it's pointless today, maybe
it isn't, but it's not the root cause of your problem anyway.

> The NULL PTR check in xhci_check_bw_table would be a second line
> of defense but as indicated in the first mail it shouldn't even get
> there.

It's an xHCI bug that BW calculation is attempted on an uninitialized
device and crashes. Looks like a NULL check somewhere is exactly what
is needed, or maybe avoid it completely on EP0 (it's probably no-op).

Other similar bug recently:
https://lore.kernel.org/linux-usb/D3CKQQAETH47.1MUO22RTCH2O3@matfyz.cz/T/#u

Yours too should be unique to those Intel Panther Point chipsets.

> As a second issue I found in usb_reset_and_verify device 
> https://github.com/torvalds/linux/blob/master/drivers/usb/core/hub.c#L6131
> 
>         ret = hub_port_init(parent_hub, udev, port1, i, &descriptor);
>         if (ret >= 0 || ret == -ENOTCONN || ret == -ENODEV) {
>             break;
>         }
> 
> hub_port_init can also return -71 / -EPROTO, the cases should be very
> rare when usb_reset_and_verify_device is triggered and that happens.

Right, and the intent seems to be to simply retry in this case.

Regards,
Michal