linux-kernel - Re: [PATCH v6 5/8] drm/i915: Check for integer truncation on the configuration of ttm place

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Date:   Mon, 15 Aug 2022 11:03:29 +0300
From:   Jani Nikula <jani.nikula@...el.com>
To:     Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
        intel-gfx@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        mchehab@...nel.org, chris@...is-wilson.co.uk,
        matthew.auld@...el.com, thomas.hellstrom@...ux.intel.com,
        nirmoy.das@...el.com, airlied@...ux.ie, daniel@...ll.ch,
        andi.shyti@...ux.intel.com, andrzej.hajda@...el.com
Subject: Re: [PATCH v6 5/8] drm/i915: Check for integer truncation on the
 configuration of ttm place

On Sat, 13 Aug 2022, Gwan-gyeong Mun <gwan-gyeong.mun@...el.com> wrote:
> There is an impedance mismatch between the first/last valid page
> frame number of ttm place in unsigned and our memory/page accounting in
> unsigned long.
> As the object size is under the control of userspace, we have to be prudent
> and catch the conversion errors.
> To catch the implicit truncation as we switch from unsigned long to
> unsigned, we use overflows_type check and report E2BIG or overflow_type
> prior to the operation.
>
> v3: Not to change execution inside a macro. (Mauro)
>     Add safe_conversion_gem_bug_on() macro and remove temporal
>     SAFE_CONVERSION() macro.
> v4: Fix unhandled GEM_BUG_ON() macro call from safe_conversion_gem_bug_on()
> v6: Fix to follow general use case for GEM_BUG_ON(). (Jani)
>
> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
> Cc: Chris Wilson <chris@...is-wilson.co.uk>
> Cc: Matthew Auld <matthew.auld@...el.com>
> Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> Cc: Jani Nikula <jani.nikula@...el.com>
> Reviewed-by: Nirmoy Das <nirmoy.das@...el.com> (v2)
> Reviewed-by: Mauro Carvalho Chehab <mchehab@...nel.org> (v3)
> Reported-by: kernel test robot <lkp@...el.com>
> Reviewed-by: Andrzej Hajda <andrzej.hajda@...el.com> (v5)
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_ttm.c |  6 +++---
>  drivers/gpu/drm/i915/intel_region_ttm.c | 22 +++++++++++++++++++---
>  2 files changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index 9f2be1892b6c..30f488712abe 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -140,14 +140,14 @@ i915_ttm_place_from_region(const struct intel_memory_region *mr,
>  	if (flags & I915_BO_ALLOC_CONTIGUOUS)
>  		place->flags |= TTM_PL_FLAG_CONTIGUOUS;
>  	if (offset != I915_BO_INVALID_OFFSET) {
> -		place->fpfn = offset >> PAGE_SHIFT;
> -		place->lpfn = place->fpfn + (size >> PAGE_SHIFT);
> +		GEM_BUG_ON(!safe_conversion(&place->fpfn, offset >> PAGE_SHIFT));
> +		GEM_BUG_ON(!safe_conversion(&place->lpfn, place->fpfn + (size >> PAGE_SHIFT)));

This would be the natural thing to do with BUG_ON/WARN_ON. And I'd like
it if we could use it like this. But, as I tried to say, GEM_BUG_ON is
nothing like BUG_ON/WARN_ON, and no code is generated for
CONFIG_DRM_I915_DEBUG_GEM=n. And our CI will never catch it because it
always has CONFIG_DRM_I915_DEBUG_GEM=y.

BR,
Jani.


>  	} else if (mr->io_size && mr->io_size < mr->total) {
>  		if (flags & I915_BO_ALLOC_GPU_ONLY) {
>  			place->flags |= TTM_PL_FLAG_TOPDOWN;
>  		} else {
>  			place->fpfn = 0;
> -			place->lpfn = mr->io_size >> PAGE_SHIFT;
> +			GEM_BUG_ON(!safe_conversion(&place->lpfn, mr->io_size >> PAGE_SHIFT));
>  		}
>  	}
>  }
> diff --git a/drivers/gpu/drm/i915/intel_region_ttm.c b/drivers/gpu/drm/i915/intel_region_ttm.c
> index 575d67bc6ffe..c480b0b50bcc 100644
> --- a/drivers/gpu/drm/i915/intel_region_ttm.c
> +++ b/drivers/gpu/drm/i915/intel_region_ttm.c
> @@ -209,14 +209,28 @@ intel_region_ttm_resource_alloc(struct intel_memory_region *mem,
>  	if (flags & I915_BO_ALLOC_CONTIGUOUS)
>  		place.flags |= TTM_PL_FLAG_CONTIGUOUS;
>  	if (offset != I915_BO_INVALID_OFFSET) {
> -		place.fpfn = offset >> PAGE_SHIFT;
> -		place.lpfn = place.fpfn + (size >> PAGE_SHIFT);
> +		if (!safe_conversion(&place.fpfn, offset >> PAGE_SHIFT)) {
> +			GEM_BUG_ON(!safe_conversion(&place.fpfn,offset >> PAGE_SHIFT));
> +			ret = -E2BIG;
> +			goto out;
> +		}
> +		if (!safe_conversion(&place.lpfn, place.fpfn + (size >> PAGE_SHIFT))) {
> +			GEM_BUG_ON(!safe_conversion(&place.lpfn,
> +						    place.fpfn + (size >> PAGE_SHIFT)));
> +			ret = -E2BIG;
> +			goto out;
> +		}
>  	} else if (mem->io_size && mem->io_size < mem->total) {
>  		if (flags & I915_BO_ALLOC_GPU_ONLY) {
>  			place.flags |= TTM_PL_FLAG_TOPDOWN;
>  		} else {
>  			place.fpfn = 0;
> -			place.lpfn = mem->io_size >> PAGE_SHIFT;
> +			if (!safe_conversion(&place.lpfn, mem->io_size >> PAGE_SHIFT)) {
> +				GEM_BUG_ON(!safe_conversion(&place.lpfn,
> +							    mem->io_size >> PAGE_SHIFT));
> +				ret = -E2BIG;
> +				goto out;
> +			}
>  		}
>  	}
>  
> @@ -224,6 +238,8 @@ intel_region_ttm_resource_alloc(struct intel_memory_region *mem,
>  	mock_bo.bdev = &mem->i915->bdev;
>  
>  	ret = man->func->alloc(man, &mock_bo, &place, &res);
> +
> +out:
>  	if (ret == -ENOSPC)
>  		ret = -ENXIO;
>  	if (!ret)

-- 
Jani Nikula, Intel Open Source Graphics Center