Re: [PATCH] xhci: Restrict USB4 tunnel detection for USB3 devices to Intel hosts

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 27.2.2025 22.20, Greg Kroah-Hartman wrote:
> On Thu, Feb 27, 2025 at 07:45:29PM +0000, Marc Zyngier wrote:
>> When adding support for USB3-over-USB4 tunnelling detection, a check
>> for an Intel-specific capability was added. This capability, which
>> goes by ID 206, is used without any check that we are actually
>> dealing with an Intel host.
>>
>> As it turns out, the Cadence XHCI controller *also* exposes an
>> extended capability numbered 206 (for unknown purposes), but of
>> course doesn't have the Intel-specific registers that the tunnelling
>> code is trying to access. Fun follows.
>>
>> The core of the problems is that the tunnelling code blindly uses
>> vendor-specific capabilities without any check (the Intel-provided
>> documentation I have at hand indicates that 192-255 are indeed
>> vendor-specific).
>>
>> Restrict the detection code to Intel HW for real, preventing any
>> further explosion on my (non-Intel) HW.
>>
>> Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: stable@vger.kernel.org
>> Fixes: 948ce83fbb7df ("xhci: Add USB4 tunnel detection for USB3 devices on Intel hosts")
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>>   drivers/usb/host/xhci-hub.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
>> index 9693464c05204..69c278b64084b 100644
>> --- a/drivers/usb/host/xhci-hub.c
>> +++ b/drivers/usb/host/xhci-hub.c
>> @@ -12,6 +12,7 @@
>>   #include <linux/slab.h>
>>   #include <linux/unaligned.h>
>>   #include <linux/bitfield.h>
>> +#include <linux/pci.h>
>>   
>>   #include "xhci.h"
>>   #include "xhci-trace.h"
>> @@ -770,9 +771,16 @@ static int xhci_exit_test_mode(struct xhci_hcd *xhci)
>>   enum usb_link_tunnel_mode xhci_port_is_tunneled(struct xhci_hcd *xhci,
>>   						struct xhci_port *port)
>>   {
>> +	struct usb_hcd *hcd;
>>   	void __iomem *base;
>>   	u32 offset;
>>   
>> +	/* Don't try and probe this capability for non-Intel hosts */
>> +	hcd = xhci_to_hcd(xhci);
>> +	if (!dev_is_pci(hcd->self.controller) ||
>> +	    to_pci_dev(hcd->self.controller)->vendor != PCI_VENDOR_ID_INTEL)
>> +		return USB_LINK_UNKNOWN;
> 
> Ugh, nice catch.
> 
> Mathias, want me to just take this directly for now and not wait for you
> to resend it?

Yes, please, take it directly

Acked-by: Mathias Nyman <mathias.nyman@linux.intel.com>

Thanks
Mathias