linux-kernel - Re: Faking MMIO ops? Fooling a driver

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Message-ID: <BANLkTi=V4Ys5uT9TrG5NjJ3JuqBVGTshsw@mail.gmail.com>
Date:	Thu, 16 Jun 2011 23:53:18 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Pekka Paalanen <pq@....fi>
Cc:	Larry Finger <Larry.Finger@...inger.net>,
	linux-wireless@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Faking MMIO ops? Fooling a driver

W dniu 16 czerwca 2011 23:47 użytkownik Rafał Miłecki
<zajec5@...il.com> napisał:
> W dniu 16 czerwca 2011 21:34 użytkownik Pekka Paalanen <pq@....fi> napisał:
>> On Thu, 16 Jun 2011 21:19:04 +0200
>> Rafał Miłecki <zajec5@...il.com> wrote:
>>
>>> W dniu 16 czerwca 2011 20:07 użytkownik Larry Finger
>>> <Larry.Finger@...inger.net> napisał:
>>> > On 06/16/2011 12:20 PM, Rafał Miłecki wrote:
>>> >>
>>> >> W dniu 16 czerwca 2011 16:44 użytkownik Rafał Miłecki
>>> >> <zajec5@...il.com>  napisał:
>>> >>>
>>> >>> I analyze MMIO dumps of closed source driver and found such a
>>> >>> place: W 2 3855.911536 9 0xb06003fc 0x810 0x0 0
>>> >>> R 2 3855.911540 9 0xb06003fe 0x0 0x0 0
>>> >>> W 2 3855.911541 9 0xb06003fe 0x0 0x0 0
>>> >>>
>>> >>> After translation:
>>> >>>  phy_read(0x0810) ->  0x0000
>>> >>> phy_write(0x0810)<- 0x0000
>>> >>>
>>> >>> So it's quite obvious, the driver is reading PHY register,
>>> >>> masking it and writing masked value. Unfortunately from just
>>> >>> looking at such place we can not guess the mask driver uses.
>>> >>>
>>> >>> I'd like to fake value read from 0xb06003fe to be 0xFFFF.
>>> >>> Is there some ready method for doing such a trick?
>>> >>>
>>> >>> Dump comes from Kernel hacking → Tracers → MMIO and
>>> >>> ndiswrapper.
>>> >>
>>> >> I can see values in MMIO trace struct are filled in
>>> >> arch/x86/mm/mmio-mod.c in "pre" and "post". However still no
>>> >> idea how to hack the returned value.
>>
>> If you want to do it that way, the idea is to overwrite
>> the right CPU register in mmio-mod.c:post(). You would test for
>> the address you want to mess with, and then "invert"
>> get_ins_reg_val() to overwrite the register with your own value.
>
> Good, idea thanks!

Implementation attached.
Now I only need to track writes to 0xfaafc3fc (that register is for
addressing to-follow PHY read/write) and wait for 0xfaafc3fe which is
read of PHY register value.

-- 
Rafał

Download attachment "mmio.fake.0xfaafc000.patch" of type "application/octet-stream" (2974 bytes)