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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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?

thanks,

greg k-h