Re: [PATCH v8 2/2] drm/gem: Don't map imported GEMs

Christian König
2022-07-05T11:39:35Z

Am 01.07.22 um 11:02 schrieb Dmitry Osipenko:
> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
> handle imported dma-bufs properly, which results in mapping of something
> else than the imported dma-buf. On NVIDIA Tegra we get a hard lockup when
> userspace writes to the memory mapping of a dma-buf that was imported into
> Tegra's DRM GEM.
>
> Majority of DRM drivers prohibit mapping of the imported GEM objects.
> Mapping of imported GEMs require special care from userspace since it
> should sync dma-buf because mapping coherency of the exporter device may
> not match the DRM device. Let's prohibit the mapping for all DRM drivers
> for consistency.
>
> Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

I'm pretty sure that this is the right approach, but it's certainly more
than possible that somebody abused this already.

Anyway patch is Reviewed-by: Christian König <christian.koenig@amd.com>
since you are really fixing a major stability problem here.

Regards,
Christian.

> ---
> drivers/gpu/drm/drm_gem.c | 4 ++++
> drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
> 2 files changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 86d670c71286..fc9ec42fa0ab 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1034,6 +1034,10 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
> {
> int ret;
>
> + /* Don't allow imported objects to be mapped */
> + if (obj->import_attach)
> + return -EINVAL;
> +
> /* Check for valid size. */
> if (obj_size < vma->vm_end - vma->vm_start)
> return -EINVAL;
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 8ad0e02991ca..6190f5018986 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -609,17 +609,8 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
> */
> int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct *vma)
> {
> - struct drm_gem_object *obj = &shmem->base;
> int ret;
>
> - if (obj->import_attach) {
> - /* Drop the reference drm_gem_mmap_obj() acquired.*/
> - drm_gem_object_put(obj);
> - vma->vm_private_data = NULL;
> -
> - return dma_buf_mmap(obj->dma_buf, vma, 0);
> - }
> -
> ret = drm_gem_shmem_get_pages(shmem);
> if (ret) {
> drm_gem_vm_close(vma);