Re: [PATCH v1 2/4] coresight: etm4x: Don't use virtual contextID for non-root PID namespace

[Suzuki K Poulose <suzuki.poulose@arm.com>]

Hi Leo

On 31/10/2021 14:42, Leo Yan wrote:
> 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, and it can leak kernel information.
> 
> For this reason, when a process runs in non-root PID namespace, the
> driver doesn't allow contextID 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, it returns
> failure if current process runs in non-root PID namespace.
> 
> Signed-off-by: Leo Yan <leo.yan@linaro.org>

Patch looks good to me. Please see minor comment below.


> ---
>   .../coresight/coresight-etm4x-sysfs.c         | 28 +++++++++++++++++++
>   1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> index e4c8c44d04ef..e218281703b0 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> @@ -2111,6 +2111,13 @@ 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_active_pid_ns(current) != &init_pid_ns)
> +		return -EINVAL;
> +
>   	spin_lock(&drvdata->spinlock);
>   	val = (unsigned long)config->vmid_val[config->vmid_idx];
>   	spin_unlock(&drvdata->spinlock);
> @@ -2125,6 +2132,13 @@ 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_active_pid_ns(current) != &init_pid_ns)

Please could we add a helper function to make this obvious ?

e.g: task_is_in_root_ns(task) ?

Suzuki