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

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Date:	Sun, 29 Aug 2010 15:39:09 +0200
From:	Matteo Croce <matteo@...nwrt.org>
To:	"H. Peter Anvin" <hpa@...or.com>
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 Sat, Aug 28, 2010 at 1:07 AM, H. Peter Anvin <hpa@...or.com> wrote:
> 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.
>
>

If the parsing fails due get_user returning error I call
`do_invalid_op(regs, error_code);`
which is the default handler, which does the page fault.
to check the CS I do `regs->cs != __USER_CS` but how to check the IP value?
convert_ip_to_linear() and then check something?

-- 
Matteo Croce
OpenWrt developer
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