linux-kernel - Re: [PATCH 10/11] powerpc: use non-set

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Date:   Mon, 17 Aug 2020 17:47:55 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org
Cc:     linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/11] powerpc: use non-set_fs based maccess routines



Le 17/08/2020 à 09:32, Christoph Hellwig a écrit :
> Provide __get_kernel_nofault and __put_kernel_nofault routines to
> implement the maccess routines without messing with set_fs and without
> opening up access to user space.

__get_user_size() opens access to user space. You have to use 
__get_user_size_allowed() when user access is already allowed (or when 
not needed to allow it).

Christophe

> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   arch/powerpc/include/asm/uaccess.h | 16 ++++++++++++++++
>   1 file changed, 16 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index 00699903f1efca..a31de40ac00b62 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -623,4 +623,20 @@ do {									\
>   		__put_user_goto(*(u8*)(_src + _i), (u8 __user *)(_dst + _i), e);\
>   } while (0)
>   
> +#define HAVE_GET_KERNEL_NOFAULT
> +
> +#define __get_kernel_nofault(dst, src, type, err_label)			\
> +do {									\
> +	int __kr_err;							\
> +									\
> +	__get_user_size(*((type *)(dst)), (__force type __user *)(src),	\
> +			sizeof(type), __kr_err);			\
> +	if (unlikely(__kr_err))						\
> +		goto err_label;						\
> +} while (0)
> +
> +#define __put_kernel_nofault(dst, src, type, err_label)			\
> +	__put_user_size_goto(*((type *)(src)),				\
> +		(__force type __user *)(dst), sizeof(type), err_label)
> +
>   #endif	/* _ARCH_POWERPC_UACCESS_H */
>