linux-kernel - Re: [PATCH] riscv: uaccess: fix type of 0 variable on error in get

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Message-ID: <20221229173447.qhcaamchxv5jkbpo@hetzy.fluff.org>
Date:   Thu, 29 Dec 2022 17:34:47 +0000
From:   Ben Dooks <ben@...ff.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     ben-linux@...ff.org, linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org, aou@...s.berkeley.edu
Subject: Re: [PATCH] riscv: uaccess: fix type of 0 variable on error in
 get_user()

On Thu, Dec 29, 2022 at 09:31:27AM -0800, Palmer Dabbelt wrote:
> On Thu, 29 Dec 2022 09:05:45 PST (-0800), ben-linux@...ff.org wrote:
> > If the get_user(x, ptr) has x as a pointer, then the setting
> > of (x) = 0 is going to produce the following sparse warning,
> > so fix this by forcing the type of 'x' when access_ok() fails.
> > 
> > fs/aio.c:2073:21: warning: Using plain integer as NULL pointer
> > 
> > Signed-off-by: Ben Dooks <ben-linux@...ff.org>
> > ---
> >  arch/riscv/include/asm/uaccess.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
> > index 855450bed9f5..ec0cab9fbddd 100644
> > --- a/arch/riscv/include/asm/uaccess.h
> > +++ b/arch/riscv/include/asm/uaccess.h
> > @@ -165,7 +165,7 @@ do {								\
> >  	might_fault();						\
> >  	access_ok(__p, sizeof(*__p)) ?		\
> >  		__get_user((x), __p) :				\
> > -		((x) = 0, -EFAULT);				\
> > +		((x) = (__force __typeof__(x))0, -EFAULT);	\
> >  })
> > 
> >  #define __put_user_asm(insn, x, ptr, err)			\
> 
> Looks like arm64 has a pretty similar pattern.  They've got the __force
> __typeof__ already, but given the similarity it might be worth refactoring
> these to share the error checking code.

I looked there for an idea on how to fix.

> Reviewed-by: Palmer Dabbelt <palmer@...osinc.com>
> 
> I'll give this a bit of time like usual, unless anyone's opposed I'll put it
> on fixes.  I wasn't planning on sending a PR this week anyway due to the
> holidays.

Ok, it's a warning which would be nice to be fixed.

-- 
Ben Dooks, ben@...ff.org, http://www.fluff.org/ben/

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