drm/i915: Check for integer truncation on the configuration of ttm place

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.

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>

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);
+		safe_conversion_gem_bug_on(&place->fpfn, offset >> PAGE_SHIFT);
+		safe_conversion_gem_bug_on(&place->lpfn, place->fpfn + (size >> PAGE_SHIFT));
 	} 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;
+			safe_conversion_gem_bug_on(&place->lpfn, mr->io_size >> PAGE_SHIFT);
 		}
 	}
 }

drivers/gpu/drm/i915/i915_gem.h

@@ -83,5 +83,9 @@ struct drm_i915_private;
 #endif
 
 #define I915_GEM_IDLE_TIMEOUT (HZ / 5)
+#define safe_conversion_gem_bug_on(ptr, value) ({ \
+	safe_conversion(ptr, value) ? 1 \
+		: (({ GEM_BUG_ON(overflows_type(value, *ptr)); }), 0); \
+})
 
 #endif /* __I915_GEM_H__ */

drivers/gpu/drm/i915/intel_region_ttm.c

@@ -209,21 +209,35 @@ 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_gem_bug_on(&place.fpfn,
+						offset >> PAGE_SHIFT)) {
+			ret = -E2BIG;
+			goto out;
+		}
+		if (!safe_conversion_gem_bug_on(&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_gem_bug_on(&place.lpfn,
+							mem->io_size >> PAGE_SHIFT)) {
+				ret = -E2BIG;
+				goto out;
+			}
 		}
 	}
 
 	mock_bo.base.size = size;
 	mock_bo.bdev = &mem->i915->bdev;
 
 	ret = man->func->alloc(man, &mock_bo, &place, &res);
+
+out:
 	if (ret == -ENOSPC)
 		ret = -ENXIO;
 	if (!ret)