Re: [PATCH 2/2] x86/uaccess: Fix casting in put_user

[David Laight <david.laight.linux@gmail.com>]

On Tue, 25 Aug 2026 23:15:02 +0200
Ricardo Ribalda <ribalda@chromium.org> wrote:

> Hi Dave
> 
> On Tue, 25 Aug 2026 at 23:06, Dave Hansen <dave.hansen@intel.com> wrote:
> >
> > On 8/25/26 13:02, Ricardo Ribalda wrote:  
> > > Recent versions of smatch preserved the address space qualifiers with
> > > typeof()[1].
> > >
> > > This fix has discovered an invalid casting in put_user.
> > >
> > > This patch fixes tens of smatch errors like the following:
> > > drivers/media/usb/uvc/uvc_v4l2.c:1112:13: warning: incorrect type in argument 2 (different address spaces)
> > > drivers/media/usb/uvc/uvc_v4l2.c:1112:13:    expected void const *from
> > > drivers/media/usb/uvc/uvc_v4l2.c:1112:13:    got unsigned int __user *  
> >
> > Could we beef up the changelog here a bit, please?
> >
> > What _is_ the invalid casting?
> >
> > What is the fix?
> >
> > Why does it work?  
> 
> Something like this would be better? I will send a v2 if there are no
> more comments.
> 
> 
> Recent versions of smatch preserved the address space qualifiers with
> typeof()[1].
> 
> This fix has discovered an invalid casting in put_user.
> 
> put_user is using a casting with __typeof__(*(ptr)), which keeps the
> qualifiers (__user), instead it should use the macro TYPEOF_UNQUAL()
> that will use __typeof_unqual__ where the compiler supports it.
> __typeof_unqual__ copies the type but not the qualifiers.

This is a spares 'bug'.
You need to fix it without changing normal compiles.

There are enough put_user() calls that is will slow down compiles.

David

> 
> 
> This patch fixes tens of smatch errors like the following:
> drivers/media/usb/uvc/uvc_v4l2.c:1112:13: warning: incorrect type in
> argument 2 (different address spaces)
> drivers/media/usb/uvc/uvc_v4l2.c:1112:13:    expected void const *from
> drivers/media/usb/uvc/uvc_v4l2.c:1112:13:    got unsigned int __user *
> 
> [1] https://github.com/error27/smatch/commit/e53027a4e816a772403baafa83c09e4a94c1cb8f
> 
>