[Intel-gfx] [PATCH v2] drm/i915: Sanity check the computed size and base of stolen memory

[Chris Wilson]

Just do a quick check that the stolen memory address range doesn't
overflow our chosen integer type.

v2: Add add_overflows() to utils with the promise that gcc7 can do this
better than C and then maybe it will have a proper definition in core.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_stolen.c | 2 +-
 drivers/gpu/drm/i915/i915_utils.h      | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
index 42bbc4b04fd6..f3abdc27c5dd 100644
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -189,7 +189,7 @@ static dma_addr_t i915_stolen_to_dma(struct drm_i915_private *dev_priv)
 		base = tom - tseg_size - ggtt->stolen_size;
 	}
 
-	if (base == 0)
+	if (base == 0 || add_overflows(base, ggtt->stolen_size))
 		return 0;
 
 	/* make sure we don't clobber the GTT if it's within stolen memory */
diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index 34020873e1f6..69e00c94ee13 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -25,6 +25,13 @@
 #ifndef __I915_UTILS_H
 #define __I915_UTILS_H
 
+#if GCC_VERSION >= 70000
+#define add_overflows(A, B) \
+	__builtin_add_overflow_p((A), (B), (typeof((A) + (B)))0)
+#else
+#define add_overflows(A, B) ((A) + (B) < (A))
+#endif
+
 #define range_overflows(start, size, max) ({ \
 	typeof(start) start__ = (start); \
 	typeof(size) size__ = (size); \
-- 
2.11.0