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Subject: Re: [char-misc-next] Revert "mei: hdcp: Replace one-element array
 with flexible-array member"
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To:     "Winkler, Tomas" <tomas.winkler@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     "Usyskin, Alexander" <alexander.usyskin@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>
References: <20200728214139.3129532-1-tomas.winkler@intel.com>
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Message-ID: <fe8f4b91-c65e-0664-c5df-52d4a93734b5@embeddedor.com>
Date:   Tue, 28 Jul 2020 18:16:51 -0500
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On 7/28/20 18:04, Gustavo A. R. Silva wrote:
> Tomas,
> 
> Please, see some comments below...
> 
> On 7/28/20 17:29, Winkler, Tomas wrote:
>>>>>>
>>>>>> Hi Tomas,
>>>>>>
>>>>>> On 7/28/20 16:41, Tomas Winkler wrote:
>>>>>>> Greg please revert, this commit it changes size of struct
>>>>>>> wired_cmd_repeater_auth_stream_req_in, this is not what firmware
>>>>>>> is expecting.
>>>>>>
>>>>>> Could you elaborate on what's the firmware expecting, exactly?
>>>>> struct wired_cmd_repeater_auth_stream_req_in {
>>>>>   -	struct hdcp2_streamid_type	streams[1];
>>>>>   + 	struct hdcp2_streamid_type	streams[];
>>>>> }
>>>>>
>>>>> But then you have, which you haven't changed to + 1 byte =
>>>>> mei_cldev_send(cldev, (u8 *)&verify_mprime_in,
>>>>>                               sizeof(verify_mprime_in));
>>>>>
> 
> I don't think the fix for this is to add 1 byte, if any, it seems
> to be sizeof(*data->streams), or sizeof(struct hdcp2_streamid_type)
> what needs to be added.
> 
> But it might be better to code something like this, instead:
> 
> diff --git a/drivers/misc/mei/hdcp/mei_hdcp.c b/drivers/misc/mei/hdcp/mei_hdcp.c
> index e6c3dc595617..7fe63c915548 100644
> --- a/drivers/misc/mei/hdcp/mei_hdcp.c
> +++ b/drivers/misc/mei/hdcp/mei_hdcp.c
> @@ -572,12 +572,12 @@ static int mei_hdcp_verify_mprime(struct device *dev,
>                HDCP_2_2_MPRIME_LEN);
>         drm_hdcp_cpu_to_be24(verify_mprime_in.seq_num_m, data->seq_num_m);
>         memcpy(verify_mprime_in.streams, data->streams,
> -              (data->k * sizeof(struct hdcp2_streamid_type)));
> +              (data->k * sizeof(*data->streams)));
> 
>         verify_mprime_in.k = cpu_to_be16(data->k);
> 
>         byte = mei_cldev_send(cldev, (u8 *)&verify_mprime_in,
> -                             sizeof(verify_mprime_in));
> +                             struct_size(&verify_mprime_in, streams, data->k));
>         if (byte < 0) {
>                 dev_dbg(dev, "mei_cldev_send failed. %zd\n", byte);
>                 return byte;
> 
> struct_size(&verify_mprime_in, streams, data->k) will give us the size, in bytes,
> of struct wired_cmd_repeater_auth_stream_req_in plus the size in bytes for
> the streams[] flexible-array, which is determined by struct hdcp2_streamid_type and
> data->k.
> 
> What do you think?
> 

This is even better:

diff --git a/drivers/misc/mei/hdcp/mei_hdcp.c b/drivers/misc/mei/hdcp/mei_hdcp.c
index e6c3dc595617..852374565cba 100644
--- a/drivers/misc/mei/hdcp/mei_hdcp.c
+++ b/drivers/misc/mei/hdcp/mei_hdcp.c
@@ -572,12 +572,12 @@ static int mei_hdcp_verify_mprime(struct device *dev,
               HDCP_2_2_MPRIME_LEN);
        drm_hdcp_cpu_to_be24(verify_mprime_in.seq_num_m, data->seq_num_m);
        memcpy(verify_mprime_in.streams, data->streams,
-              (data->k * sizeof(struct hdcp2_streamid_type)));
+              flex_array_size(&verify_mprime_in, streams, data->k));

        verify_mprime_in.k = cpu_to_be16(data->k);

        byte = mei_cldev_send(cldev, (u8 *)&verify_mprime_in,
-                             sizeof(verify_mprime_in));
+                             struct_size(&verify_mprime_in, streams, data->k));
        if (byte < 0) {
                dev_dbg(dev, "mei_cldev_send failed. %zd\n", byte);
                return byte;

the flex_array_size() is a new helper that was designed for this situations. :)
It calculates the size of a flexible array member within an enclosing structure,
which is exactly the case.

Thanks
--
Gustavo

> See more comments below...
> 
>>>>
>>>> I see, this is the kind of feedback I need from people that knows the
>>>> code better. Thanks!
>>>>
>>>>> But that's not the major point. Point is that we should be able to
>>>>> review and test the code before it is merged.  You haven't run it, right?
>>>>> There is MAINTAINERS file for a reason.
>>>>>
>>>>
>>>> I'm using this command:
>>>>
>>>> $ scripts/get_maintainer.pl --nokeywords --nogit --nogit-fallback
>>>>
>>>> and this is the output for both files:
>>>>
>>>> $ scripts/get_maintainer.pl --nokeywords --nogit --nogit-fallback
>>>> drivers/misc/mei/hdcp/mei_hdcp.c Arnd Bergmann <arnd@arndb.de>
>>>> (supporter:CHAR and MISC DRIVERS) Greg Kroah-Hartman
>>>> <gregkh@linuxfoundation.org> (supporter:CHAR and MISC DRIVERS) linux-
>>>> kernel@vger.kernel.org (open list) $ scripts/get_maintainer.pl
>>>> --nokeywords -- nogit --nogit-fallback
>>>> drivers/misc/mei/hdcp/mei_hdcp.h Arnd Bergmann <arnd@arndb.de>
>>>> (supporter:CHAR and MISC DRIVERS) Greg Kroah-Hartman
>>>> <gregkh@linuxfoundation.org> (supporter:CHAR and MISC DRIVERS) linux-
>>>> kernel@vger.kernel.org (open list)
>>>
>>>
>>>> For some reason you don't appear on the list above. Do you see
>>>> anything wrong with the command I'm running to get the maintainers and
>>> lists?
>>>
>>> Not sure, it should be caught by drivers/misc/mei/* ?
>>> Maybe it is not recursive? Need to check the script, frankly I usually check this
>>> manually.
>>>
>>> INTEL MANAGEMENT ENGINE (mei)
>>> M:      Tomas Winkler <tomas.winkler@intel.com>
>>> L:      linux-kernel@vger.kernel.org
>>> S:      Supported
>>> F:      Documentation/driver-api/mei/*
>>> F:      drivers/misc/mei/*
>>> F:      drivers/watchdog/mei_wdt.c
>>> F:      include/linux/mei_cl_bus.h
>>> F:      include/uapi/linux/mei.h
>>> F:      samples/mei/*
>>>
>>
>> It's not recursive, when I add drivers/misc/mei/hdcp/* . It works correctly 
>> I will post a patch.
>>
> 
> Great. I'm glad we got to the root cause of this issue. :)
> 
> Thanks
> --
> Gustavo
> 
>> Thanks
>> Tomas
>>
>>
>>>
>>>>
>>>> Thanks
>>>> --
>>>> Gustavo
>>>>
>>>>>>
>>>>>>> I really do not appreciate that the code is bypassing driver
>>>>>>> maintaner review, I think this is a minimum we can ask for, this
>>>>>>> is not for a first time.
>>>>>>>
>>>>>>> This reverts commit c56967d674e361ebe716e66992e3c5332b25ac1f.
>>>>>>>
>>>>>>> Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
>>>>>>> Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
>>>>>>> ---
>>>>>>>  drivers/misc/mei/hdcp/mei_hdcp.c | 2 +-
>>>>>>> drivers/misc/mei/hdcp/mei_hdcp.h | 2 +-
>>>>>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/misc/mei/hdcp/mei_hdcp.c
>>>>>>> b/drivers/misc/mei/hdcp/mei_hdcp.c
>>>>>>> index d1d3e025ca0e..e6c3dc595617 100644
>>>>>>> --- a/drivers/misc/mei/hdcp/mei_hdcp.c
>>>>>>> +++ b/drivers/misc/mei/hdcp/mei_hdcp.c
>>>>>>> @@ -572,7 +572,7 @@ static int mei_hdcp_verify_mprime(struct
>>>>>>> device
>>>>>> *dev,
>>>>>>>  	       HDCP_2_2_MPRIME_LEN);
>>>>>>>  	drm_hdcp_cpu_to_be24(verify_mprime_in.seq_num_m, data-
>>>> seq_num_m);
>>>>>>>  	memcpy(verify_mprime_in.streams, data->streams,
>>>>>>> -	       array_size(data->k, sizeof(*data->streams)));
>>>>>>> +	       (data->k * sizeof(struct hdcp2_streamid_type)));
>>>>>>>
>>>>>>>  	verify_mprime_in.k = cpu_to_be16(data->k);
>>>>>>>
>>>>>>> diff --git a/drivers/misc/mei/hdcp/mei_hdcp.h
>>>>>>> b/drivers/misc/mei/hdcp/mei_hdcp.h
>>>>>>> index 834757f5e072..18ffc773fa18 100644
>>>>>>> --- a/drivers/misc/mei/hdcp/mei_hdcp.h
>>>>>>> +++ b/drivers/misc/mei/hdcp/mei_hdcp.h
>>>>>>> @@ -358,7 +358,7 @@ struct
>>> wired_cmd_repeater_auth_stream_req_in
>>>> {
>>>>>>>  	u8
>>>>>> 	seq_num_m[HDCP_2_2_SEQ_NUM_LEN];
>>>>>>>  	u8				m_prime[HDCP_2_2_MPRIME_LEN];
>>>>>>>  	__be16				k;
>>>>>>> -	struct hdcp2_streamid_type	streams[];
>>>>>>> +	struct hdcp2_streamid_type	streams[1];
>>>>>>>  } __packed;
>>>>>>>
>>>>>>>  struct wired_cmd_repeater_auth_stream_req_out {
>>>>>>>