Re: [PATCH] drm/panthor: Restrict high priorities on group_create

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue,  3 Sep 2024 16:49:55 +0200
Mary Guillemard <mary.guillemard@collabora.com> wrote:

> We were allowing any users to create a high priority group without any
> permission checks. As a result, this was allowing possible denial of
> service.
> 
> We now only allow the DRM master or users with the CAP_SYS_NICE
> capability to set higher priorities than PANTHOR_GROUP_PRIORITY_MEDIUM.
> 
> As the sole user of that uAPI lives in Mesa and hardcode a value of
> MEDIUM [1], this should be safe to do.
> 
> Additionally, as those checks are performed at the ioctl level,
> panthor_group_create now only check for priority level validity.
> 
> [1]https://gitlab.freedesktop.org/mesa/mesa/-/blob/f390835074bdf162a63deb0311d1a6de527f9f89/src/gallium/drivers/panfrost/pan_csf.c#L1038
> 
> Signed-off-by: Mary Guillemard <mary.guillemard@collabora.com>
> Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
> Cc: stable@vger.kernel.org

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_drv.c   | 23 +++++++++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_sched.c |  2 +-
>  include/uapi/drm/panthor_drm.h          |  6 +++++-
>  3 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index b5e7b919f241..34182f67136c 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -10,6 +10,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
>  
> +#include <drm/drm_auth.h>
>  #include <drm/drm_debugfs.h>
>  #include <drm/drm_drv.h>
>  #include <drm/drm_exec.h>
> @@ -996,6 +997,24 @@ static int panthor_ioctl_group_destroy(struct drm_device *ddev, void *data,
>  	return panthor_group_destroy(pfile, args->group_handle);
>  }
>  
> +static int group_priority_permit(struct drm_file *file,
> +				 u8 priority)
> +{
> +	/* Ensure that priority is valid */
> +	if (priority > PANTHOR_GROUP_PRIORITY_HIGH)
> +		return -EINVAL;
> +
> +	/* Medium priority and below are always allowed */
> +	if (priority <= PANTHOR_GROUP_PRIORITY_MEDIUM)
> +		return 0;
> +
> +	/* Higher priorities require CAP_SYS_NICE or DRM_MASTER */
> +	if (capable(CAP_SYS_NICE) || drm_is_current_master(file))
> +		return 0;
> +
> +	return -EACCES;
> +}
> +
>  static int panthor_ioctl_group_create(struct drm_device *ddev, void *data,
>  				      struct drm_file *file)
>  {
> @@ -1011,6 +1030,10 @@ static int panthor_ioctl_group_create(struct drm_device *ddev, void *data,
>  	if (ret)
>  		return ret;
>  
> +	ret = group_priority_permit(file, args->priority);
> +	if (ret)
> +		return ret;
> +
>  	ret = panthor_group_create(pfile, args, queue_args);
>  	if (ret >= 0) {
>  		args->group_handle = ret;
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index c426a392b081..91a31b70c037 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -3092,7 +3092,7 @@ int panthor_group_create(struct panthor_file *pfile,
>  	if (group_args->pad)
>  		return -EINVAL;
>  
> -	if (group_args->priority > PANTHOR_CSG_PRIORITY_HIGH)
> +	if (group_args->priority >= PANTHOR_CSG_PRIORITY_COUNT)
>  		return -EINVAL;
>  
>  	if ((group_args->compute_core_mask & ~ptdev->gpu_info.shader_present) ||
> diff --git a/include/uapi/drm/panthor_drm.h b/include/uapi/drm/panthor_drm.h
> index 926b1deb1116..e23a7f9b0eac 100644
> --- a/include/uapi/drm/panthor_drm.h
> +++ b/include/uapi/drm/panthor_drm.h
> @@ -692,7 +692,11 @@ enum drm_panthor_group_priority {
>  	/** @PANTHOR_GROUP_PRIORITY_MEDIUM: Medium priority group. */
>  	PANTHOR_GROUP_PRIORITY_MEDIUM,
>  
> -	/** @PANTHOR_GROUP_PRIORITY_HIGH: High priority group. */
> +	/**
> +	 * @PANTHOR_GROUP_PRIORITY_HIGH: High priority group.
> +	 *
> +	 * Requires CAP_SYS_NICE or DRM_MASTER.
> +	 */
>  	PANTHOR_GROUP_PRIORITY_HIGH,
>  };
>  
> 
> base-commit: a15710027afb40c7c1e352902fa5b8c949f021de