Re: [PATCH] riscv: uaccess: fix type of 0 variable on error in get_user()

From: Ben Dooks <ben@fluff.org>
To: Palmer Dabbelt <palmer@dabbelt.com>
Cc: ben-linux@fluff.org, linux-riscv@lists.infradead.org,
	Paul Walmsley <paul.walmsley@sifive.com>,
	linux-kernel@vger.kernel.org, aou@eecs.berkeley.edu
Subject: Re: [PATCH] riscv: uaccess: fix type of 0 variable on error in get_user()
Date: Thu, 29 Dec 2022 17:34:47 +0000	[thread overview]
Message-ID: <20221229173447.qhcaamchxv5jkbpo@hetzy.fluff.org> (raw)
In-Reply-To: <mhng-33b9aafc-448a-4400-9a06-cb222724363a@palmer-ri-x1c9>

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@fluff.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@fluff.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@rivosinc.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@fluff.org, http://www.fluff.org/ben/

Large Hadron Colada: A large Pina Colada that makes the universe disappear.

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