linux-kernel - Re: [PATCH] staging: goldfish: fix direct copy_to_user() from _

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Message-ID: <1403521128.27368.2.camel@acox1-desk.ger.corp.intel.com>
Date:	Mon, 23 Jun 2014 11:58:48 +0100
From:	Alan Cox <alan@...ux.intel.com>
To:	James A Shackleford <shack@...ux.com>
Cc:	gregkh@...uxfoundation.org, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: goldfish: fix direct copy_to_user() from
 __iomem

On Sun, 2014-06-22 at 03:29 -0400, James A Shackleford wrote:
> This patch allocates a few pages and performs an ioread8_rep() from the bus
> address, which are then copied to userspace.  This fixes the sparse warning:
> 
> drivers/staging/goldfish/goldfish_audio.c:136:43: warning: incorrect type in argument 2 (different address spaces)
> drivers/staging/goldfish/goldfish_audio.c:136:43:    expected void const *from
> drivers/staging/goldfish/goldfish_audio.c:136:43:    got char [noderef] <asn:2>*read_buffer
> 
> which was a result of performing a copy_to_user() directly from the bus address
> to the userspace, which can be unsafe across some architectures.

Goldfish is a specific architecture. It shouldn't be doing direct
xcopies like that - which is why the code is in staging but at the same
time allocating a buffer each call and doing extra copies is not the
right answer.

It should be mapping the pages when they are first set up.

Alan


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