linux-kernel - Re: [PATCH 2/3] kernel.h: add u64_to_user

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Date:	Wed, 20 Apr 2016 18:46:16 -0700
From:	Joe Perches <joe@...ches.com>
To:	Gustavo Padovan <gustavo@...ovan.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	dri-devel@...ts.freedesktop.org,
	Daniel Stone <daniels@...labora.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Rob Clark <robdclark@...il.com>,
	Greg Hackmann <ghackmann@...gle.com>,
	John Harrison <John.C.Harrison@...el.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 2/3] kernel.h: add u64_to_user_ptr()

On Wed, 2016-04-20 at 16:18 -0300, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> 
> This function had copies in 3 different files. Unify them in kernel.h.
[]
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
[]
> @@ -53,6 +53,12 @@
> 
>  #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
>  
> +static inline void __user *u64_to_user_ptr(u64 address)
> +{
> +	typecheck(u64, address);
> +	return (void __user *)(uintptr_t)address;
> +}
> +

This won't work because by the time address is checked
address is already u64

This would need to be something like

#define u64_to_user_ptr(x)	\
({				\
	typecheck(u64, x);	\
	u64_to_user_ptr(x);	\
})