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

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

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 for ETMs use
the newly introduced kernel config CONFIG_EXCLUDE_KERNEL_HW_ITRACE
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@codeaurora.org>
---
 drivers/hwtracing/coresight/coresight-etm3x-core.c  | 11 +++++++++++
 drivers/hwtracing/coresight/coresight-etm3x-sysfs.c |  3 ++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
index 5bf5a5a4ce6d..4da3bfa66b70 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -195,6 +195,9 @@ void etm_set_default(struct etm_config *config)
 	if (WARN_ON_ONCE(!config))
 		return;
 
+	if (IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE))
+		config->mode |= ETM_MODE_EXCL_KERN;
+
 	/*
 	 * Taken verbatim from the TRM:
 	 *
@@ -239,6 +242,7 @@ void etm_set_default(struct etm_config *config)
 void etm_config_trace_mode(struct etm_config *config)
 {
 	u32 flags, mode;
+	struct etm_drvdata *drvdata = container_of(config, struct etm_drvdata, config);
 
 	mode = config->mode;
 
@@ -248,6 +252,13 @@ void etm_config_trace_mode(struct etm_config *config)
 	if (mode == (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER))
 		return;
 
+	if (!(mode & ETM_MODE_EXCL_KERN) && IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE)) {
+		dev_err(&drvdata->csdev->dev,
+			"Kernel mode tracing is not allowed, check your kernel config\n");
+		config->mode |= ETM_MODE_EXCL_KERN;
+		return;
+	}
+
 	/* nothing to do if neither flags are set */
 	if (!(mode & ETM_MODE_EXCL_KERN) && !(mode & ETM_MODE_EXCL_USER))
 		return;
diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
index e8c7649f123e..26642dafddbb 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
@@ -164,7 +164,8 @@ static ssize_t mode_store(struct device *dev,
 	else
 		config->ctrl &= ~ETMCR_RETURN_STACK;
 
-	if (config->mode & (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER))
+	if ((config->mode & (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER)) ||
+	    IS_ENABLED(CONFIG_EXCLUDE_KERNEL_HW_ITRACE))
 		etm_config_trace_mode(config);
 
 	spin_unlock(&drvdata->spinlock);
-- 
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