[PATCHv2 4/4] coresight: etm3x: Add support to exclude kernel mode tracing

[Doug Anderson]

Hi,

On Mon, Mar 1, 2021 at 11:05 AM Sai Prakash Ranjan
<saiprakash.ranjan at 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.
>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan at codeaurora.org>
> ---
>  drivers/hwtracing/coresight/coresight-etm3x-core.c  | 3 +++
>  drivers/hwtracing/coresight/coresight-etm3x-sysfs.c | 6 ++++++
>  2 files changed, 9 insertions(+)

Reviewed-by: Douglas Anderson <dianders at chromium.org>


> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> index e8c7649f123e..f522fc2e01b3 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> @@ -116,6 +116,12 @@ static ssize_t mode_store(struct device *dev,
>         if (ret)
>                 return ret;
>
> +       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");

Same nit as in patch #3 that the above string should be indented by 1
more space.