linux-kernel - Re: [PATCH v2 07/18] nios2: drop access_ok() check from __put

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Date:   Wed, 23 Feb 2022 17:30:53 -0600
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org, arnd@...db.de,
        linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Cc:     linux@...linux.org.uk, will@...nel.org, guoren@...nel.org,
        bcain@...eaurora.org, geert@...ux-m68k.org, monstr@...str.eu,
        tsbogend@...ha.franken.de, nickhu@...estech.com,
        green.hu@...il.com, shorne@...il.com, deller@....de,
        mpe@...erman.id.au, peterz@...radead.org, mingo@...hat.com,
        mark.rutland@....com, hca@...ux.ibm.com, dalias@...c.org,
        davem@...emloft.net, richard@....at, x86@...nel.org,
        jcmvbkbc@...il.com, ebiederm@...ssion.com,
        akpm@...ux-foundation.org, ardb@...nel.org,
        linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH v2 07/18] nios2: drop access_ok() check from __put_user()



On 2/16/22 07:13, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Unlike other architectures, the nios2 version of __put_user() has an
> extra check for access_ok(), preventing it from being used to implement
> __put_kernel_nofault().
> 
> Split up put_user() along the same lines as __get_user()/get_user()
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   arch/nios2/include/asm/uaccess.h | 56 +++++++++++++++++++-------------
>   1 file changed, 33 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/nios2/include/asm/uaccess.h b/arch/nios2/include/asm/uaccess.h
> index ca9285a915ef..a5cbe07cf0da 100644
> --- a/arch/nios2/include/asm/uaccess.h
> +++ b/arch/nios2/include/asm/uaccess.h
> @@ -167,34 +167,44 @@ do {									\
>   	: "r" (val), "r" (ptr), "i" (-EFAULT));				\
>   }
>   
> -#define put_user(x, ptr)						\
> +#define __put_user_common(__pu_val, __pu_ptr)				\
>   ({									\
>   	long __pu_err = -EFAULT;					\
> -	__typeof__(*(ptr)) __user *__pu_ptr = (ptr);			\
> -	__typeof__(*(ptr)) __pu_val = (__typeof(*ptr))(x);		\
> -	if (access_ok(__pu_ptr, sizeof(*__pu_ptr))) {	\
> -		switch (sizeof(*__pu_ptr)) {				\
> -		case 1:							\
> -			__put_user_asm(__pu_val, "stb", __pu_ptr, __pu_err); \
> -			break;						\
> -		case 2:							\
> -			__put_user_asm(__pu_val, "sth", __pu_ptr, __pu_err); \
> -			break;						\
> -		case 4:							\
> -			__put_user_asm(__pu_val, "stw", __pu_ptr, __pu_err); \
> -			break;						\
> -		default:						\
> -			/* XXX: This looks wrong... */			\
> -			__pu_err = 0;					\
> -			if (copy_to_user(__pu_ptr, &(__pu_val),		\
> -				sizeof(*__pu_ptr)))			\
> -				__pu_err = -EFAULT;			\
> -			break;						\
> -		}							\
> +	switch (sizeof(*__pu_ptr)) {					\
> +	case 1:								\
> +		__put_user_asm(__pu_val, "stb", __pu_ptr, __pu_err);	\
> +		break;							\
> +	case 2:								\
> +		__put_user_asm(__pu_val, "sth", __pu_ptr, __pu_err);	\
> +		break;							\
> +	case 4:								\
> +		__put_user_asm(__pu_val, "stw", __pu_ptr, __pu_err);	\
> +		break;							\
> +	default:							\
> +		/* XXX: This looks wrong... */				\
> +		__pu_err = 0;						\
> +		if (__copy_to_user(__pu_ptr, &(__pu_val),		\
> +			sizeof(*__pu_ptr)))				\
> +			__pu_err = -EFAULT;				\
> +		break;							\
>   	}								\
>   	__pu_err;							\
>   })
>   
> -#define __put_user(x, ptr) put_user(x, ptr)
> +#define __put_user(x, ptr)						\
> +({									\
> +	__auto_type __pu_ptr = (ptr);					\
> +	typeof(*__pu_ptr) __pu_val = (typeof(*__pu_ptr))(x);		\
> +	__put_user_common(__pu_val, __pu_ptr);				\
> +})
> +
> +#define put_user(x, ptr)						\
> +({									\
> +	__auto_type __pu_ptr = (ptr);					\
> +	typeof(*__pu_ptr) __pu_val = (typeof(*__pu_ptr))(x);		\
> +	access_ok(__pu_ptr, sizeof(*__pu_ptr)) ?			\
> +		__put_user_common(__pu_val, __pu_ptr) :			\
> +		-EFAULT;						\
> +})
>   
>   #endif /* _ASM_NIOS2_UACCESS_H */

Acked-by: Dinh Nguyen <dinguyen@...nel.org>