linux-kernel - Re: [PATCH v2 20/40] metag: fix put

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Date:	Wed, 7 Jan 2015 09:55:04 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	<linux-kernel@...r.kernel.org>
CC:	Arnd Bergmann <arnd@...db.de>, <linux-arch@...r.kernel.org>,
	<linux-metag@...r.kernel.org>
Subject: Re: [PATCH v2 20/40] metag: fix put_user sparse errors

On 06/01/15 15:44, Michael S. Tsirkin wrote:
> virtio wants to write bitwise types to userspace using put_user.
> At the moment this triggers sparse errors, since the value is passed
> through an integer.
> 
> For example:
> 
> 	__le32 __user *p;
> 	__le32 x;
> 	put_user(x, p);
> 
> is safe, but currently triggers a sparse warning.
> 
> Fix that up using __force.
> 
> This also fixes warnings due to writing a pointer out to
> userland.
> 
> Note: this does not suppress any useful sparse checks since callers
> do a cast (__typeof__(*(ptr))) (x) which in turn forces all the
> necessary type checks.
> 
> Suggested-by: James Hogan <james.hogan@...tec.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  arch/metag/include/asm/uaccess.h | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/metag/include/asm/uaccess.h b/arch/metag/include/asm/uaccess.h
> index c314b45..9627c19 100644
> --- a/arch/metag/include/asm/uaccess.h
> +++ b/arch/metag/include/asm/uaccess.h
> @@ -107,18 +107,23 @@ extern long __put_user_asm_w(unsigned int x, void __user *addr);
>  extern long __put_user_asm_d(unsigned int x, void __user *addr);
>  extern long __put_user_asm_l(unsigned long long x, void __user *addr);
>  
> -#define __put_user_size(x, ptr, size, retval)			\
> -do {                                                            \
> -	retval = 0;                                             \
> -	switch (size) {                                         \
> +#define __put_user_size(x, ptr, size, retval)				\
> +do {                                                            	\
> +	retval = 0;                                             	\
> +	switch (size) {                                         	\

On the last 3 lines here you've added a tab after spaces which
checkpatch complains about. With that fixed (or converted to tabs properly):

Acked-by: James Hogan <james.hogan@...tec.com>

Cheers
James

>  	case 1:								\
> -		retval = __put_user_asm_b((unsigned int)x, ptr); break;	\
> +		retval = __put_user_asm_b((__force unsigned int)x, ptr);\
> +		break;							\
>  	case 2:								\
> -		retval = __put_user_asm_w((unsigned int)x, ptr); break;	\
> +		retval = __put_user_asm_w((__force unsigned int)x, ptr);\
> +		break;							\
>  	case 4:								\
> -		retval = __put_user_asm_d((unsigned int)x, ptr); break;	\
> +		retval = __put_user_asm_d((__force unsigned int)x, ptr);\
> +		break;							\
>  	case 8:								\
> -		retval = __put_user_asm_l((unsigned long long)x, ptr); break; \
> +		retval = __put_user_asm_l((__force unsigned long long)x,\
> +					  ptr);				\
> +		break;							\
>  	default:							\
>  		__put_user_bad();					\
>  	}								\
> 


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