linux-kernel - Re: [PATCH] mailbox: pcc: fix channel calculation in get_pcc

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Message-ID: <CAJ5Y-eYdPM+hSZdH_Sz10K6iHb0cCB1E4Wh_A_sJn_yyLgLjZQ@mail.gmail.com>
Date:	Fri, 15 Jan 2016 13:22:15 -0500
From:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
To:	Alexey Klimov <alexey.klimov@....com>,
	Jaswinder Singh <jaswinder.singh@...aro.org>
Cc:	Jassi Brar <jassisinghbrar@...il.com>,
	Sudeep Holla <sudeep.holla@....com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mailbox: pcc: fix channel calculation in get_pcc_channel()

+ Jassi (Linaro addr)

On 15 January 2016 at 13:20, Ashwin Chaugule <ashwin.chaugule@...aro.org> wrote:
> Jassi,
>
> On 10 December 2015 at 13:19, Ashwin Chaugule
> <ashwin.chaugule@...aro.org> wrote:
>> On 10 December 2015 at 12:28, Alexey Klimov <alexey.klimov@....com> wrote:
>>> This patch fixes the calculation of pcc_chan for non-zero id.
>>> After the compiler ignores the (unsigned long) cast the
>>> pcc_mbox_channels pointer is type-cast and then the type-cast
>>> offset is added which results in address outside of the range
>>> leading to the kernel crashing.
>>>
>>> We might add braces and make it:
>>>
>>> pcc_chan = (struct mbox_chan *)
>>>                 ((unsigned long) pcc_mbox_channels +
>>>                 (id * sizeof(*pcc_chan)));
>>>
>>> but let's go with array approach here and use id as index.
>>>
>>> Tested on Juno board.
>>>
>>> Acked-by: Sudeep Holla <sudeep.holla@....com>
>>> Signed-off-by: Alexey Klimov <alexey.klimov@....com>
>>> ---
>>>  drivers/mailbox/pcc.c | 8 +-------
>>>  1 file changed, 1 insertion(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
>>> index 45d85ae..8f779a1 100644
>>> --- a/drivers/mailbox/pcc.c
>>> +++ b/drivers/mailbox/pcc.c
>>> @@ -81,16 +81,10 @@ static struct mbox_controller pcc_mbox_ctrl = {};
>>>   */
>>>  static struct mbox_chan *get_pcc_channel(int id)
>>>  {
>>> -       struct mbox_chan *pcc_chan;
>>> -
>>>         if (id < 0 || id > pcc_mbox_ctrl.num_chans)
>>>                 return ERR_PTR(-ENOENT);
>>>
>>> -       pcc_chan = (struct mbox_chan *)
>>> -               (unsigned long) pcc_mbox_channels +
>>> -               (id * sizeof(*pcc_chan));
>>> -
>>> -       return pcc_chan;
>>> +       return &pcc_mbox_channels[id];
>>>  }
>>>
>>
>>
>> Strange that we didn't catch this even with a non-zero id. But the
>> change makes sense so..
>>
>> Acked-by: Ashwin Chaugule <ashwin.chaugule@...aro.org>
>
> Can you please include this patch in your pull request to Linus?
>
> Thanks,
> Ashwin.