linux-kernel - Re: [PATCH] staging: vc04_services: Fixed address type mismatch in vchiq

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Date:   Thu, 18 Feb 2021 10:39:20 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Pritthijit Nath <pritthijit.nath@...oud.com>
Cc:     nsaenzjulienne@...e.de, arnd@...db.de, dan.carpenter@...cle.com,
        amarjargal16@...il.com, phil@...pberrypi.com,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] staging: vc04_services: Fixed address type mismatch in
 vchiq_arm.c

On Thu, Feb 18, 2021 at 02:40:15PM +0530, Pritthijit Nath wrote:
> This change fixes a sparse address type mismatch warning "incorrect type
> in assignment (different address spaces)".
> 
> Signed-off-by: Pritthijit Nath <pritthijit.nath@...oud.com>
> ---
>  .../staging/vc04_services/interface/vchiq_arm/vchiq_arm.c   | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> index 59e45dc03a97..3c715b926a57 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> @@ -1214,11 +1214,7 @@ static int vchiq_ioc_await_completion(struct vchiq_instance *instance,
>  		    !instance->use_close_delivered)
>  			unlock_service(service);
>  
> -		/*
> -		 * FIXME: address space mismatch, does bulk_userdata
> -		 * actually point to user or kernel memory?
> -		 */
> -		user_completion.bulk_userdata = completion->bulk_userdata;
> +		user_completion.bulk_userdata = (void __user *)completion->bulk_userdata;

So, this pointer really is user memory?

How did you determine that?

If so, why isn't this a __user * in the first place?

You can't just paper over the FIXME by doing a cast without doing the
real work here, otherwise someone wouldn't have written the FIXME :)

thanks,

greg k-h