Re: [PATCH] staging: vchip_arm: Fix misuse of %x

[Guo Zhi]

On 2021/9/23 13:19, Greg KH wrote:
> On Thu, Sep 23, 2021 at 11:55:54AM +0800, Guo Zhi wrote:
> > Pointers should be printed with %p or %px rather than
> > cast to (unsigned long) and printed with %lx.
> > Change %lx to %pK to print the pointers.
> >
> > Signed-off-by: Guo Zhi <qtxuning1999@xxxxxxxxxxx>
> > ---
> >   .../staging/vc04_services/interface/vchiq_arm/vchiq_arm.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 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 b5aac862a29..408e5fe710b 100644
> > --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> > +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> > @@ -591,11 +591,11 @@ service_callback(enum vchiq_reason reason, struct vchiq_header *header,
> >   		return VCHIQ_SUCCESS;
> >   
> >   	vchiq_log_trace(vchiq_arm_log_level,
> > -		"%s - service %lx(%d,%p), reason %d, header %lx, instance %lx, bulk_userdata %lx",
> > -		__func__, (unsigned long)user_service,
> > +		"%s - service %pK(%d,%p), reason %d, header %pK, instance %pK, bulk_userdata %pK",
> > +		__func__, user_service,
> >   		service->localport, user_service->userdata,
> > -		reason, (unsigned long)header,
> > -		(unsigned long)instance, (unsigned long)bulk_userdata);
> > +		reason, header,
> > +		instance, bulk_userdata);
> Why print this out at all?  What uses this?  Can it just be deleted?
>
> thanks,
>
> greg k-h

This information is printed for debugging usage.

But malicious user process can also print it through debugfs at 
/sys/kernel/debug.

As it can be used for debugging, it's a little radical to just delete.

Therefore, I suggest replacing %lx with %pK to avoid kernel address leakage.

thanks,

Guo