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Date:   Fri, 22 May 2020 16:04:40 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     kbuild test robot <lkp@intel.com>, kbuild-all@lists.01.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [vfs:uaccess.net 16/19] net/atm/ioctl.c:180:29: sparse: sparse:
 Using plain integer as NULL pointer
Message-ID: <20200522150440.GQ23230@ZenIV.linux.org.uk>
References: <202005222158.Heq0Iqum%lkp@intel.com>
 <20200522142321.GP23230@ZenIV.linux.org.uk>
 <20200522144439.GC26492@gaia>
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On Fri, May 22, 2020 at 03:44:40PM +0100, Catalin Marinas wrote:
> On Fri, May 22, 2020 at 03:23:21PM +0100, Al Viro wrote:
> > On Fri, May 22, 2020 at 09:58:00PM +0800, kbuild test robot wrote:
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git uaccess.net
> > > head:   0edecc020b33f8e31d8baa80735b45e8e8434700
> > > commit: a3929484af75ee524419edbbc4e9ce012c3d67c9 [16/19] atm: move copyin from atm_getnames() into the caller
> > > config: arm64-randconfig-s002-20200521 (attached as .config)
> > > compiler: aarch64-linux-gcc (GCC) 9.3.0
> > > reproduce:
> > >         # apt-get install sparse
> > >         # sparse version: v0.6.1-193-gb8fad4bc-dirty
> > >         git checkout a3929484af75ee524419edbbc4e9ce012c3d67c9
> > >         # save the attached .config to linux build tree
> > >         make W=1 C=1 ARCH=arm64 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
> > > 
> > > If you fix the issue, kindly add following tag as appropriate
> > > Reported-by: kbuild test robot <lkp@intel.com>
> > > 
> > > 
> > > sparse warnings: (new ones prefixed by >>)
> > > 
> > > >> net/atm/ioctl.c:180:29: sparse: sparse: Using plain integer as NULL pointer
> > 
> > Huh?
> > 
> > >  > 180				if (get_user(buf, &iobuf->buffer))
> > 
> > _what_ use of plain integer as a NULL pointer?  <looks>
> > Misannotated get_user() on arm64 - should be
> > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> > index 32fc8061aa76..bc5c7b091152 100644
> > --- a/arch/arm64/include/asm/uaccess.h
> > +++ b/arch/arm64/include/asm/uaccess.h
> > @@ -304,7 +304,7 @@ do {									\
> >  		__p = uaccess_mask_ptr(__p);				\
> >  		__raw_get_user((x), __p, (err));			\
> >  	} else {							\
> > -		(x) = 0; (err) = -EFAULT;				\
> > +		(x) = (__force __typeof__(x))0; (err) = -EFAULT;	\
> >  	}								\
> >  } while (0)
> >  
> > and that's a _lot_ of noise in sparse logs on arm64, obviously - one for
> > each get_user() of a pointer...
> 
> Thanks for pointing this out. We seem to do the right thing for
> __raw_get_user() but missed one path in __get_user_error().
> 
> Since you wrote the patch already, are you ok for me to add some text
> and your signed-off-by?

Sure, np...