linux-kernel - Re: Lock up when faking MMIO read[bwl] on some machines [WAS: Faking MMIO ops? Fooling a driver]

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Message-ID: <BANLkTikT3qoZhTrd0uF-JNehNhTCRjF6kw@mail.gmail.com>
Date:	Sat, 18 Jun 2011 12:57:26 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Pekka Paalanen <pq@....fi>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-wireless@...r.kernel.org,
	Larry Finger <Larry.Finger@...inger.net>
Subject: Re: Lock up when faking MMIO read[bwl] on some machines [WAS: Faking
 MMIO ops? Fooling a driver]

W dniu 18 czerwca 2011 12:39 użytkownik Pekka Paalanen <pq@....fi> napisał:
> On Sat, 18 Jun 2011 00:31:32 +0200
> Rafał Miłecki <zajec5@...il.com> wrote:
>
>> I use attached patch to fake result of read[bwl] performed by
>> closed source driver (ndiswrapper+bcmwl and wl).
>>
>> 1) It works great on my Sony VAIO with Intel(R) Core(TM)2 Duo CPU
>> P8400 2) It locks up Macbook Pro 8,1 with some 8-cores Intel
>>
>> Do you have any idea why it causes the lockup? Function causing
>> problem is "set_ins_reg_val". I've created it as copy of
>> get_ins_reg_val, it just sets values in struct pt_regs, instead of
>> reading them).
>
> Sorry, I have no insight to that... does unmodified mmiotrace
> work properly? Are you tracing the exact same kernel binary blob
> on both machines? Maybe it's using some rare instruction
> mmiotrace does not decode properly? Maybe with a rep prefix?
> Do those CPUs have any differences in their registers or
> struct pt_regs?
>
> I'm not even sure how "legal" it is to poke pt_regs there. :-/

Not modified MMIO tracing works great on this machine, I've grabbed
dumps 10-20 times without a lock up or anything.

I'm using different drivers on both machines, because Macbook Pro 8,1
has unique BCM4331 card that I can not buy and that is not available
with PCI(e) slot. Is uses some vendor specific, PCIe compatible slot.
Simple commenting out "set_ins_reg_val" work fine on this Macbook, PHY
reads are tracked correctly.

As for differences in struct pt_regs... yeah, I think that happens.
I'm using x86 kernel, while on Macbook we use x86_64 as it's required
to use 64bit driver in ndiswrapper.

I can try to find out, which register we try to overwrite on Macbook.

-- 
Rafał
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