coresight: etm4x: Don't use virtual contextID for non-root PID namespace

As commented in the function ctxid_pid_store(), it can cause the PID
values mismatching between context ID tracing and PID allocated in a
non-root namespace.

For this reason, when a process runs in non-root PID namespace, the
driver doesn't allow PID tracing and returns failure when access
contextID related sysfs nodes.

VMID works for virtual contextID when the kernel runs in EL2 mode with
VHE; on the other hand, the driver doesn't prevent users from accessing
it when programs run in the non-root namespace.  Thus this can lead
to same issues with contextID described above.

This patch imposes the checking on VMID related sysfs knobs and returns
failure if current process runs in non-root PID namespace.
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20220204152403.71775-3-leo.yan@linaro.org

drivers/hwtracing/coresight/coresight-etm4x-sysfs.c

@@ -2115,6 +2115,13 @@ static ssize_t vmid_val_show(struct device *dev,
 	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
 	struct etmv4_config *config = &drvdata->config;
 
+	/*
+	 * Don't use virtual contextID tracing if coming from a PID namespace.
+	 * See comment in ctxid_pid_store().
+	 */
+	if (!task_is_in_init_pid_ns(current))
+		return -EINVAL;
+
 	spin_lock(&drvdata->spinlock);
 	val = (unsigned long)config->vmid_val[config->vmid_idx];
 	spin_unlock(&drvdata->spinlock);
@@ -2129,6 +2136,13 @@ static ssize_t vmid_val_store(struct device *dev,
 	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
 	struct etmv4_config *config = &drvdata->config;
 
+	/*
+	 * Don't use virtual contextID tracing if coming from a PID namespace.
+	 * See comment in ctxid_pid_store().
+	 */
+	if (!task_is_in_init_pid_ns(current))
+		return -EINVAL;
+
 	/*
 	 * only implemented when vmid tracing is enabled, i.e. at least one
 	 * vmid comparator is implemented and at least 8 bit vmid size
@@ -2152,6 +2166,13 @@ static ssize_t vmid_masks_show(struct device *dev,
 	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
 	struct etmv4_config *config = &drvdata->config;
 
+	/*
+	 * Don't use virtual contextID tracing if coming from a PID namespace.
+	 * See comment in ctxid_pid_store().
+	 */
+	if (!task_is_in_init_pid_ns(current))
+		return -EINVAL;
+
 	spin_lock(&drvdata->spinlock);
 	val1 = config->vmid_mask0;
 	val2 = config->vmid_mask1;
@@ -2169,6 +2190,13 @@ static ssize_t vmid_masks_store(struct device *dev,
 	struct etmv4_config *config = &drvdata->config;
 	int nr_inputs;
 
+	/*
+	 * Don't use virtual contextID tracing if coming from a PID namespace.
+	 * See comment in ctxid_pid_store().
+	 */
+	if (!task_is_in_init_pid_ns(current))
+		return -EINVAL;
+
 	/*
 	 * only implemented when vmid tracing is enabled, i.e. at least one
 	 * vmid comparator is implemented and at least 8 bit vmid size