Re: [PATCH 2/2] drm/i915: Check that the DMA address for stolen fits within dma_addr_t

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Jan 27, 2017 at 04:55:31PM +0000, Chris Wilson wrote:
> Just sanity check that the value we deduce from the stolen memory
> register fits within the kernel's dma_addr_t and doesn't overflow.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_stolen.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index 42bbc4b04fd6..4f1f3090c0ed 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -211,6 +211,14 @@ static dma_addr_t i915_stolen_to_dma(struct drm_i915_private *dev_priv)
>  			ggtt_start &= PGTBL_ADDRESS_LO_MASK;
>  		ggtt_end = ggtt_start + ggtt_total_entries(ggtt) * 4;
>  
> +		if (ggtt_end <= ggtt_start ||
> +		    overflows_type(ggtt_end, dma_addr_t)) {
> +			DRM_ERROR("DMA address for reserved igfx memory [%llx - %llx] does not fit within the kernel's %db dma_addr_t\n",
> +				  ggtt_start, ggtt_end,
> +				  (int)sizeof(dma_addr_t) * 8);
> +			return 0;
> +		}

This would only check if the ggtt location fits into dma_addr_t.
We don't need that since we never touch the ggtt directly with
either the CPU or GPU. So I think this piece of code should keep
on using u64 as it needs to be able to hold the 36 address we read
from the hardware/firmware.

> +
>  		if (ggtt_start >= stolen[0].start && ggtt_start < stolen[0].end)
>  			stolen[0].end = ggtt_start;
>  		if (ggtt_end > stolen[1].start && ggtt_end <= stolen[1].end)
> -- 
> 2.11.0

-- 
Ville Syrjälä
Intel OTC
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