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

[Gwan-gyeong Mun]

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 at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld at intel.com>
Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das at intel.com> (v2)
Reviewed-by: Mauro Carvalho Chehab <mchehab at kernel.org> (v3)
Reported-by: kernel test robot <lkp at intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda at intel.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)));
 	} 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)
-- 
2.34.1