[Intel-gfx] [PATCH v2 1/2] drm/i915/userptr: add user_size limit check

[Chris Wilson]

Quoting Matthew Auld (2020-01-16 20:31:49)
> Don't allow a mismatch between obj->base.size/vma->size and the actual
> number of pages for the backing store, which is limited to INT_MAX
> pages.
> 
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> index e5558af111e2..fef96a303d9d 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> @@ -768,6 +768,18 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
>         if (args->flags & ~(I915_USERPTR_READ_ONLY |
>                             I915_USERPTR_UNSYNCHRONIZED))
>                 return -EINVAL;
> +       /*
> +        * 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 (args->user_size >> PAGE_SHIFT > INT_MAX)
> +               return -E2BIG;

I'm convinced that the following patch is the last bug (excusing
i915_gem_internal.c), and think we should commit to removing this limit.
-Chris