[PATCH 3/6] drm/i915: Check for integer truncation on the configuration of ttm place

[Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx>]

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 our overflows_type check and report E2BIG or overflow_type
prior to the operation.

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 12 +++++++++---
 drivers/gpu/drm/i915/intel_region_ttm.c | 16 +++++++++++++---
 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 52f8c3f4d8a8..8231a6fc5437 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -137,19 +137,25 @@ i915_ttm_place_from_region(const struct intel_memory_region *mr,
 	if (mr->type == INTEL_MEMORY_SYSTEM)
 		return;
 
+#define SAFE_CONVERSION(ptr, value) ({ \
+	if (!safe_conversion(ptr, value)) { \
+		GEM_BUG_ON(overflows_type(value, *ptr)); \
+	} \
+})
 	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(&place->fpfn, offset >> PAGE_SHIFT);
+		SAFE_CONVERSION(&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(&place->lpfn, mr->io_size >> PAGE_SHIFT);
 		}
 	}
+#undef SAFE_CONVERSION
 }
 
 static void
diff --git a/drivers/gpu/drm/i915/intel_region_ttm.c b/drivers/gpu/drm/i915/intel_region_ttm.c
index 62ff77445b01..8fcb8654b978 100644
--- a/drivers/gpu/drm/i915/intel_region_ttm.c
+++ b/drivers/gpu/drm/i915/intel_region_ttm.c
@@ -202,24 +202,34 @@ intel_region_ttm_resource_alloc(struct intel_memory_region *mem,
 	struct ttm_resource *res;
 	int ret;
 
+#define SAFE_CONVERSION(ptr, value) ({ \
+	if (!safe_conversion(ptr, value)) { \
+		GEM_BUG_ON(overflows_type(value, *ptr)); \
+		ret = -E2BIG; \
+		goto out; \
+	} \
+})
 	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(&place.fpfn, offset >> PAGE_SHIFT);
+		SAFE_CONVERSION(&place.lpfn, place.fpfn + (size >> PAGE_SHIFT));
 	} 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;
+			SAFE_CONVERSION(&place.lpfn, mem->io_size >> PAGE_SHIFT);
 		}
 	}
+#undef SAFE_CONVERSION
 
 	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)
-- 
2.34.1