[PATCH v5] drm/mediatek: Fix coverity issue with unintentional integer overflow

[Jason-JH.Lin]

1. Instead of multiplying 2 variable of different types. Change to
assign a value of one variable and then multiply the other variable.

2. Add a int variable for multiplier calculation instead of calculating
different types multiplier with dma_addr_t variable directly.

Fixes: 1a64a7aff8da ("drm/mediatek: Fix cursor plane no update")
Signed-off-by: Jason-JH.Lin <jason-jh.lin at mediatek.com>
Reviewed-by: Alexandre Mergnat <amergnat at baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
---
Change in v5:
Add 'coverity issue' in title and code comments.
---
 drivers/gpu/drm/mediatek/mtk_drm_gem.c   |  9 +++++-
 drivers/gpu/drm/mediatek/mtk_drm_plane.c | 39 ++++++++++++++++++------
 2 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
index 9f364df52478..f6632a0fe509 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
@@ -121,7 +121,14 @@ int mtk_drm_gem_dumb_create(struct drm_file *file_priv, struct drm_device *dev,
 	int ret;
 
 	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
-	args->size = args->pitch * args->height;
+
+	/*
+	 * Multiply 2 variables of different types,
+	 * for example: args->size = args->spacing * args->height;
+	 * may cause coverity issue with unintentional overflow.
+	 */
+	args->size = args->pitch;
+	args->size *= args->height;
 
 	mtk_gem = mtk_drm_gem_create(dev, args->size, false);
 	if (IS_ERR(mtk_gem))
diff --git a/drivers/gpu/drm/mediatek/mtk_drm_plane.c b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
index db2f70ae060d..5acb03b7c6fe 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
@@ -141,6 +141,7 @@ static void mtk_plane_update_new_state(struct drm_plane_state *new_state,
 	dma_addr_t addr;
 	dma_addr_t hdr_addr = 0;
 	unsigned int hdr_pitch = 0;
+	int offset;
 
 	gem = fb->obj[0];
 	mtk_gem = to_mtk_gem_obj(gem);
@@ -150,8 +151,15 @@ static void mtk_plane_update_new_state(struct drm_plane_state *new_state,
 	modifier = fb->modifier;
 
 	if (modifier == DRM_FORMAT_MOD_LINEAR) {
-		addr += (new_state->src.x1 >> 16) * fb->format->cpp[0];
-		addr += (new_state->src.y1 >> 16) * pitch;
+		/*
+		 * Using dma_addr_t variable to calculate with multiplier of different types,
+		 * for example: addr += (new_state->src.x1 >> 16) * fb->format->cpp[0];
+		 * may cause coverity issue with unintentional overflow.
+		 */
+		offset = (new_state->src.x1 >> 16) * fb->format->cpp[0];
+		addr += offset;
+		offset = (new_state->src.y1 >> 16) * pitch;
+		addr += offset;
 	} else {
 		int width_in_blocks = ALIGN(fb->width, AFBC_DATA_BLOCK_WIDTH)
 				      / AFBC_DATA_BLOCK_WIDTH;
@@ -159,21 +167,34 @@ static void mtk_plane_update_new_state(struct drm_plane_state *new_state,
 				       / AFBC_DATA_BLOCK_HEIGHT;
 		int x_offset_in_blocks = (new_state->src.x1 >> 16) / AFBC_DATA_BLOCK_WIDTH;
 		int y_offset_in_blocks = (new_state->src.y1 >> 16) / AFBC_DATA_BLOCK_HEIGHT;
-		int hdr_size;
+		int hdr_size, hdr_offset;
 
 		hdr_pitch = width_in_blocks * AFBC_HEADER_BLOCK_SIZE;
 		pitch = width_in_blocks * AFBC_DATA_BLOCK_WIDTH *
 			AFBC_DATA_BLOCK_HEIGHT * fb->format->cpp[0];
 
 		hdr_size = ALIGN(hdr_pitch * height_in_blocks, AFBC_HEADER_ALIGNMENT);
+		hdr_offset = hdr_pitch * y_offset_in_blocks +
+			AFBC_HEADER_BLOCK_SIZE * x_offset_in_blocks;
+
+		/*
+		 * Using dma_addr_t variable to calculate with multiplier of different types,
+		 * for example: addr += hdr_pitch * y_offset_in_blocks;
+		 * may cause coverity issue with unintentional overflow.
+		 */
+		hdr_addr = addr + hdr_offset;
 
-		hdr_addr = addr + hdr_pitch * y_offset_in_blocks +
-			   AFBC_HEADER_BLOCK_SIZE * x_offset_in_blocks;
 		/* The data plane is offset by 1 additional block. */
-		addr = addr + hdr_size +
-		       pitch * y_offset_in_blocks +
-		       AFBC_DATA_BLOCK_WIDTH * AFBC_DATA_BLOCK_HEIGHT *
-		       fb->format->cpp[0] * (x_offset_in_blocks + 1);
+		offset = pitch * y_offset_in_blocks +
+			 AFBC_DATA_BLOCK_WIDTH * AFBC_DATA_BLOCK_HEIGHT *
+			 fb->format->cpp[0] * (x_offset_in_blocks + 1);
+
+		/*
+		 * Using dma_addr_t variable to calculate with multiplier of different types,
+		 * for example: addr += pitch * y_offset_in_blocks;
+		 * may cause coverity issue with unintentional overflow.
+		 */
+		addr = addr + hdr_size + offset;
 	}
 
 	mtk_plane_state->pending.enable = true;
-- 
2.18.0