[Intel-gfx] [PATCH] drm/i915/dmabuf: don't trust the dma_buf->size

[Chris Wilson]

Quoting Matthew Auld (2021-01-22 15:56:28)
> At least for the time being, we need to limit our object sizes such that
> the number of pages can fit within a 32b signed int. It looks like we
> should also apply the same restriction to any imported dma-buf.
> 
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index 04e9c04545ad..dc11497f830b 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -244,6 +244,16 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
>                 }
>         }
>  
> +       /*
> +        * XXX: There is a prevalence of the assumption that we fit the
> +        * object's page count inside a 32bit _signed_ variable. Let's document
> +        * this and catch if we ever need to fix it. In the meantime, if you do
> +        * spot such a local variable, please consider fixing!
> +        */
> +
> +       if (dma_buf->size >> PAGE_SHIFT > INT_MAX)
> +               return ERR_PTR(-E2BIG);

Just to be a pain, let's consolidate these together so we don't forget.

i915_gem.h or i915_gem_object.h?
/*
 * XXX: There is a prevalence of the assumption that we fit the
 * object's page count inside a 32bit _signed_ variable. Let's document
 * this and catch if we ever need to fix it. In the meantime, if you do
 * spot such a local variable, please consider fixing!
 */
#define GEM_CHECK_SIZE_OVERFLOW(sz) \
	GEM_WARN_ON((sz) >> PAGE_SHIFT > INT_MAX)
-Chris