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

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Date:   Thu, 29 Dec 2022 09:31:27 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     ben-linux@...ff.org
CC:     linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org, aou@...s.berkeley.edu,
        ben-linux@...ff.org
Subject:     Re: [PATCH] riscv: uaccess: fix type of 0 variable on error in get_user()

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.

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.

Thanks!