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

[Doug Anderson]

Hi,

On Mon, Mar 1, 2021 at 11:05 AM Sai Prakash Ranjan
<saiprakash.ranjan@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> ---
>  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@xxxxxxxxxxxx>


> --- 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.  ;-)