Subject: Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()

From: Yury Norov <[email-masked]>
Date: Mon, 27 Apr 2026 13:58:51 -0400

On Mon, Apr 27, 2026 at 07:13:48PM +0200, Christophe Leroy (CS GROUP) wrote:
> At the time being, x86 and arm64 are missing unsafe_copy_from_user().

No, they don't. They (should) rely on a generic implementation from
linux/uaccess.h, like every other arch, except for  PPC and RISCV.

But they #define arch_unsafe_get_user, and the unsafe_copy_from_user()
becomes undefined conditionally on that.

So please, fix that bug instead of introducing another arch flavor.
We'd always choose generic version, unless there's strong evidence
that arch one is better.  

Thanks,
Yury
 
> Add it.
> 
> Signed-off-by: Christophe Leroy (CS GROUP) <[email-masked]>
> ---
>  arch/x86/include/asm/uaccess.h | 29 ++++++++++++++++++++++++-----
>  1 file changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 3a0dd3c2b233..10c458ffa399 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -598,7 +598,7 @@ _label:									\
>   * We want the unsafe accessors to always be inlined and use
>   * the error labels - thus the macro games.
>   */
> -#define unsafe_copy_loop(dst, src, len, type, label)				\
> +#define unsafe_put_loop(dst, src, len, type, label)				\
>  	while (len >= sizeof(type)) {						\
>  		unsafe_put_user(*(type *)(src),(type __user *)(dst),label);	\
>  		dst += sizeof(type);						\
> @@ -611,10 +611,29 @@ do {									\
>  	char __user *__ucu_dst = (_dst);				\
>  	const char *__ucu_src = (_src);					\
>  	size_t __ucu_len = (_len);					\
> -	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);	\
> -	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
> -	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
> -	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
> +	unsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);	\
> +	unsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
> +	unsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
> +	unsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
> +} while (0)
> +
> +#define unsafe_get_loop(dst, src, len, type, label)				\
> +	while (len >= sizeof(type)) {						\
> +		unsafe_get_user(*(type __user *)(src),(type *)(dst),label);	\
> +		dst += sizeof(type);						\
> +		src += sizeof(type);						\
> +		len -= sizeof(type);						\
> +	}
> +
> +#define unsafe_copy_from_user(_dst,_src,_len,label)			\
> +do {									\
> +	char *__ucu_dst = (_dst);					\
> +	const char __user *__ucu_src = (_src);				\
> +	size_t __ucu_len = (_len);					\
> +	unsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);	\
> +	unsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
> +	unsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
> +	unsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
>  } while (0)
>  
>  #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
> -- 
> 2.49.0
>