linux-kernel - Re: [PATCH RESEND] xhci: Use xhci_get_virt_ep() to validate ep

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Date:   Fri, 29 Apr 2022 12:36:26 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Mayank Rana <quic_mrana@...cinc.com>, peter.chen@...nel.org,
        balbi@...nel.org, stern@...land.harvard.edu,
        chunfeng.yun@...iatek.com, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH RESEND] xhci: Use xhci_get_virt_ep() to validate ep_index

On Fri, Apr 29, 2022 at 01:23:50PM +0300, Mathias Nyman wrote:
> On 29.4.2022 13.02, Greg KH wrote:
> > On Fri, Apr 29, 2022 at 12:49:59PM +0300, Mathias Nyman wrote:
> >> On 28.4.2022 22.04, Mayank Rana wrote:
> >>> ring_doorbell_for_active_rings() API is being called from
> >>> multiple context. This specific API tries to get virt_dev
> >>> based endpoint using passed slot_id and ep_index. Some caller
> >>> API is having check against slot_id and ep_index using
> >>> xhci_get_virt_ep() API whereas xhci_handle_cmd_config_ep() API
> >>> only check ep_index against -1 value but not upper bound i.e.
> >>> EP_CTX_PER_DEV. Hence use xhci_get_virt_ep() API to get virt_dev
> >>> based endpoint which checks both slot_id and ep_index to get
> >>> valid endpoint.
> >>
> >> ep_index upper bound is known to be in range as EP_CTX_PER_DEV is 31,
> >> and ep_index = fls(u32 value)  - 1 - 1; 
> >>
> >> We can change to use xhci_get_virt_ep(), but this would be more useful
> >> earlier in xhci_handle_cmd_config_ep() where we touch the ep before
> >> calling ring_doorbell_for_active_rings()
> >>
> >> Also note that this codepath is only used for some prototype
> >> xHC controller that probably never made it to the market about 10 years ago.
> > 
> > Can we just delete the codepath entirely then?
> 
> Probably.
> Commit ac9d8fe7c6a8 USB: xhci: Add quirk for Fresco Logic xHCI hardware.
> that added this states:
> 
> "This patch is for prototype hardware that will be given to other companies
> for evaluation purposes only, and should not reach consumer hands.  Fresco
> Logic's next chip rev should have this bug fixed."
> 
> Should we print some warning instead if this controller is used?
> just in case. 

Would be a good idea, see if that hardware did actually get out into the
wild.

thanks,

greg k-h