linux-kernel - Re: AMD Geode NOPL emulation for kernel 2.6.36-rc2

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Date:	Fri, 27 Aug 2010 16:07:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matteo Croce <matteo@...nwrt.org>
CC:	Thomas Backlund <tmb@...driva.org>, linux-kernel@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Natale Vinto <ebballon@...il.com>
Subject: Re: AMD Geode NOPL emulation for kernel 2.6.36-rc2

On 08/27/2010 02:32 PM, Matteo Croce wrote:
> can I ignore the return value when I expect val to be non zero?
> the doc says: "On error, the variable @x is set to zero."

No.  You need to deliver a page fault to the application in this case.

The *real* test for this kind of crap is correct page fault behavior,
and so forth.

Also, at the very least you need to check for:

- CS == USER_CS
- IP in the proper range for user space

Your patch in its current form is one big security hole.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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