[PATCH 3/8] drm/panthor: Fix UAF in panthor_gem_create_with_handle() debugfs code

[Adrián Larumbe]

Hi Simona,

On 28.05.2025 11:13, Simona Vetter wrote:
> The object is potentially already gone after the drm_gem_object_put().
> In general the object should be fully constructed before calling
> drm_gem_handle_create(), except the debugfs tracking uses a separate
> lock and list and separate flag to denotate whether the object is
> actually initilized.
>
> Since I'm touching this all anyway simplify this by only adding the
> object to the debugfs when it's ready for that, which allows us to
> delete that separate flag. panthor_gem_debugfs_bo_rm() already checks
> whether we've actually been added to the list or this is some error
> path cleanup.
>
> Fixes: a3707f53eb3f ("drm/panthor: show device-wide list of DRM GEM objects over DebugFS")
> Cc: Adrián Larumbe <adrian.larumbe at collabora.com>
> Cc: Boris Brezillon <boris.brezillon at collabora.com>
> Cc: Steven Price <steven.price at arm.com>
> Cc: Liviu Dudau <liviu.dudau at arm.com>
> Signed-off-by: Simona Vetter <simona.vetter at intel.com>
> Signed-off-by: Simona Vetter <simona.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 31 +++++++++++++--------------
>  drivers/gpu/drm/panthor/panthor_gem.h |  3 ---
>  2 files changed, 15 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 7c00fd77758b..f334444cb5df 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -16,9 +16,11 @@
>  #include "panthor_mmu.h"
>
>  #ifdef CONFIG_DEBUG_FS
> -static void panthor_gem_debugfs_bo_add(struct panthor_device *ptdev,
> -				       struct panthor_gem_object *bo)
> +static void panthor_gem_debugfs_bo_add(struct panthor_gem_object *bo)
>  {
> +	struct panthor_device *ptdev = container_of(bo->base.base.dev,
> +						    struct panthor_device, base);
> +
>  	INIT_LIST_HEAD(&bo->debugfs.node);
>
>  	bo->debugfs.creator.tgid = current->group_leader->pid;
> @@ -44,12 +46,10 @@ static void panthor_gem_debugfs_bo_rm(struct panthor_gem_object *bo)
>
>  static void panthor_gem_debugfs_set_usage_flags(struct panthor_gem_object *bo, u32 usage_flags)
>  {
> -	bo->debugfs.flags = usage_flags | PANTHOR_DEBUGFS_GEM_USAGE_FLAG_INITIALIZED;
> +	bo->debugfs.flags = usage_flags;
> +	panthor_gem_debugfs_bo_add(bo);
>  }
>  #else
> -static void panthor_gem_debugfs_bo_add(struct panthor_device *ptdev,
> -				       struct panthor_gem_object *bo)
> -{}
>  static void panthor_gem_debugfs_bo_rm(struct panthor_gem_object *bo) {}
>  static void panthor_gem_debugfs_set_usage_flags(struct panthor_gem_object *bo, u32 usage_flags) {}
>  #endif
> @@ -246,7 +246,7 @@ struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t
>  	drm_gem_gpuva_set_lock(&obj->base.base, &obj->gpuva_list_lock);
>  	mutex_init(&obj->label.lock);
>
> -	panthor_gem_debugfs_bo_add(ptdev, obj);
> +	INIT_LIST_HEAD(&obj->debugfs.node);

This is going to break builds with no DebugFS support.

>  	return &obj->base.base;
>  }
> @@ -285,6 +285,12 @@ panthor_gem_create_with_handle(struct drm_file *file,
>  		bo->base.base.resv = bo->exclusive_vm_root_gem->resv;
>  	}
>
> +	/*
> +	 * No explicit flags are needed in the call below, since the
> +	 * function internally sets the INITIALIZED bit for us.
> +	 */

If we got rid of the INITIALIZED usage flag, then this comment should also be reworded.

> +	panthor_gem_debugfs_set_usage_flags(bo, 0);
> +
>  	/*
>  	 * Allocate an id of idr table where the obj is registered
>  	 * and handle has the id what user can see.
> @@ -296,12 +302,6 @@ panthor_gem_create_with_handle(struct drm_file *file,
>  	/* drop reference from allocate - handle holds it now. */
>  	drm_gem_object_put(&shmem->base);
>
> -	/*
> -	 * No explicit flags are needed in the call below, since the
> -	 * function internally sets the INITIALIZED bit for us.
> -	 */
> -	panthor_gem_debugfs_set_usage_flags(bo, 0);
> -
>  	return ret;
>  }
>
> @@ -387,7 +387,7 @@ static void panthor_gem_debugfs_bo_print(struct panthor_gem_object *bo,
>  	unsigned int refcount = kref_read(&bo->base.base.refcount);
>  	char creator_info[32] = {};
>  	size_t resident_size;
> -	u32 gem_usage_flags = bo->debugfs.flags & (u32)~PANTHOR_DEBUGFS_GEM_USAGE_FLAG_INITIALIZED;
> +	u32 gem_usage_flags = bo->debugfs.flags;
>  	u32 gem_state_flags = 0;
>
>  	/* Skip BOs being destroyed. */
> @@ -436,8 +436,7 @@ void panthor_gem_debugfs_print_bos(struct panthor_device *ptdev,
>
>  	scoped_guard(mutex, &ptdev->gems.lock) {
>  		list_for_each_entry(bo, &ptdev->gems.node, debugfs.node) {
> -			if (bo->debugfs.flags & PANTHOR_DEBUGFS_GEM_USAGE_FLAG_INITIALIZED)
> -				panthor_gem_debugfs_bo_print(bo, m, &totals);
> +			panthor_gem_debugfs_bo_print(bo, m, &totals);
>  		}
>  	}
>
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index 4dd732dcd59f..8fc7215e9b90 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.h
> +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> @@ -35,9 +35,6 @@ enum panthor_debugfs_gem_usage_flags {
>
>  	/** @PANTHOR_DEBUGFS_GEM_USAGE_FLAG_FW_MAPPED: BO is mapped on the FW VM. */
>  	PANTHOR_DEBUGFS_GEM_USAGE_FLAG_FW_MAPPED = BIT(PANTHOR_DEBUGFS_GEM_USAGE_FW_MAPPED_BIT),
> -
> -	/** @PANTHOR_DEBUGFS_GEM_USAGE_FLAG_INITIALIZED: BO is ready for DebugFS display. */
> -	PANTHOR_DEBUGFS_GEM_USAGE_FLAG_INITIALIZED = BIT(31),
>  };
>
>  /**
> --
> 2.49.0

There's a Panfrost port of the functionality this patch fixes pending merge into drm-misc,
so I should probably ask either Boris or Steven to hold off on merging them till I've made
sure there's no potential UAF in it.

Adrian Larumbe