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

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Message-ID: <CAD=FV=XCi_+yW6DPeUYmtjMhn-qpjMiB0E4_Qkz6d_e6G-CoVA@mail.gmail.com>
Date:   Mon, 1 Mar 2021 14:43:41 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Leo Yan <leo.yan@...aro.org>, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>, coresight@...ts.linaro.org,
        Stephen Boyd <swboyd@...omium.org>,
        Denis Nikitin <denik@...omium.org>,
        Mattias Nissler <mnissler@...omium.org>,
        Al Grant <al.grant@....com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv2 3/4] coresight: etm4x: Add support to exclude kernel
 mode tracing

Hi,

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


> --- 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.  ;-)