Re: [PATCHv2 3/4] coresight: etm4x: Add support to exclude kernel mode tracing

[Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>]

On 2021-03-02 04:13, Doug Anderson wrote:
> Hi,
> 
> On Mon, Mar 1, 2021 at 11:05 AM Sai Prakash Ranjan
> <saiprakash.ranjan@codeaurora.org> wrote:
>> 
>> On production systems with ETMs enabled, it is preferred to exclude
>> kernel mode(NS EL1) tracing for security concerns and support only
>> userspace(NS EL0) tracing. Perf subsystem interface uses the newly
>> introduced kernel config CONFIG_EXCLUDE_KERNEL_PMU_TRACE to exclude
>> kernel mode tracing, but there is an additional interface via sysfs
>> for ETMs which also needs to be handled to exclude kernel
>> mode tracing. So we use this same generic kernel config to handle
>> the sysfs mode of tracing. This config is disabled by default and
>> would not affect the current configuration which has both kernel and
>> userspace tracing enabled by default.
>> 
>> Tested-by: Denis Nikitin <denik@chromium.org>
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>> ---
>>  drivers/hwtracing/coresight/coresight-etm4x-core.c  | 6 +++++-
>>  drivers/hwtracing/coresight/coresight-etm4x-sysfs.c | 6 ++++++
>>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> Not that I'm an expert in the perf subsystem, but the concern I had
> with v1 is now addressed.  FWIW this seems fine to me now.
> 
> Reviewed-by: Douglas Anderson <dianders@chromium.org>
> 

Thanks Doug.

> 
>> --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
>> @@ -296,6 +296,12 @@ static ssize_t mode_store(struct device *dev,
>>         if (kstrtoul(buf, 16, &val))
>>                 return -EINVAL;
>> 
>> +       if (IS_ENABLED(CONFIG_EXCLUDE_KERNEL_PMU_TRACE) && (!(val & 
>> ETM_MODE_EXCL_KERN))) {
>> +               dev_warn(dev,
>> +                       "Kernel mode tracing is not allowed, check 
>> your kernel config\n");
> 
> slight nit that I think your string needs to be indented by 1 space.  
> ;-)
> 

Ah yes, I will have to post v3 anyways to fix commit message in Patch 2
after I get few more feedback for other patches, I will fix this up as 
well.

Thanks,
Sai

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