Re: [PATCH] coresight: fix the wrong type of the trace_id in coresight_path

[Jie Gan <quic_jiegan@quicinc.com>]

On 4/1/2025 5:56 PM, Mike Leach wrote:
> Hi,
> 
> On Tue, 1 Apr 2025 at 07:11, Anshuman Khandual
> <anshuman.khandual@arm.com> wrote:
>>
>> On 4/1/25 07:12, Jie Gan wrote:
>>> The trace_id in coresight_path may contain an error number which means a
>>> negative integer, but the current type of the trace_id is u8. Change the
>>> type to int to fix it.
>>>
>>> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
>>> Fixes: 3c03c49b2fa5 ("Coresight: Introduce a new struct coresight_path")
>>> Signed-off-by: Jie Gan <jie.gan@oss.qualcomm.com>
>>
>> LGTM
>>
>> Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
>>
>>> ---
>>>   include/linux/coresight.h | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
>>> index d79a242b271d..c2bf10c43e7c 100644
>>> --- a/include/linux/coresight.h
>>> +++ b/include/linux/coresight.h
>>> @@ -337,7 +337,7 @@ static struct coresight_dev_list (var) = {                                \
>>>    */
>>>   struct coresight_path {
>>>        struct list_head        path_list;
>>> -     u8                      trace_id;
>>> +     int                     trace_id;
>>>   };
>>>
>>>   enum cs_mode {
> 
> There are many places in the Coresight drivers that assign a u8
> traceid from the path trace ID.
> 
> e.g.
> In coresight-etm4x-core.c : etm4_enable_perf()
> 
> drvdata->trcid = path->trace_id;
> 
> drvdata->trcid is defined as a u8  - the reason being trace IDs are
> 128 bits wide with some reserved values.
> 
> Will this not just trigger the same issue if path->trace_id is changed
> to an int? Even if not it is inconsistent handling of the trace ID
> values.
> 
> Trace ID errors should be handled by returning an invalid trace ID
> value - were the trace ID value will fail the macro
> IS_VALID_CS_TRACE_ID(), or separate the return of a trace ID from an
> error return in a function.
> 

Hi Mike,

The path->trace_id is verified after it has been assigned with the logic 
you mentioned:

if (!IS_VALID_CS_TRACE_ID(path->trace_id))
	goto err_path;

So it should be safe to assign to another u8 parameter, like you mentioned:

In coresight-etm4x-core.c : etm4_enable_perf()

drvdata->trcid = path->trace_id;

Thanks,
Jie


> Regards
> 
> Mike
> 
> 
> 
> --
> Mike Leach
> Principal Engineer, ARM Ltd.
> Manchester Design Centre. UK