[PATCH v2 4/6] media: verisilicon: rockchip: bound VPU981 AV1 tile loop and guard divisor

[Michael Bommarito <michael.bommarito@gmail.com>]

rockchip_vpu981_av1_dec_set_tile_info() divides context_update_tile_id by
tile_info->tile_cols and writes one descriptor per tile into the tile_info
DMA buffer, sized for AV1_MAX_TILES. tile_cols / tile_rows come straight
from the bitstream; reject a zero column or row count and bound the grid to
AV1_MAX_TILES so the division is safe and the writes stay in the buffer.

Fixes: 727a400686a2 ("media: verisilicon: Add Rockchip AV1 decoder")
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Assisted-by: Claude:claude-opus-4-8
---
 .../verisilicon/rockchip_vpu981_hw_av1_dec.c  | 29 +++++++++++++------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c b/drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c
index e4e21ad373233..71d2ef72c4402 100644
--- a/drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c
+++ b/drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c
@@ -578,21 +578,32 @@ static void rockchip_vpu981_av1_dec_set_tile_info(struct hantro_ctx *ctx)
 	const struct v4l2_av1_tile_info *tile_info = &ctrls->frame->tile_info;
 	const struct v4l2_ctrl_av1_tile_group_entry *group_entry =
 	    ctrls->tile_group_entry;
-	int context_update_y =
-	    tile_info->context_update_tile_id / tile_info->tile_cols;
-	int context_update_x =
-	    tile_info->context_update_tile_id % tile_info->tile_cols;
-	int context_update_tile_id =
-	    context_update_x * tile_info->tile_rows + context_update_y;
+	unsigned int tile_cols, tile_rows;
+	int context_update_y, context_update_x, context_update_tile_id;
 	u8 *dst = av1_dec->tile_info.cpu;
 	struct hantro_dev *vpu = ctx->dev;
 	int tile0, tile1;
 
+	/* Guard the divisor and bound the grid to the tile_info buffer. */
+	tile_cols = tile_info->tile_cols;
+	tile_rows = tile_info->tile_rows;
+	if (!tile_cols || !tile_rows)
+		return;
+	if (tile_cols * tile_rows > AV1_MAX_TILES) {
+		tile_cols = min_t(unsigned int, tile_cols, AV1_MAX_TILES);
+		tile_rows = min_t(unsigned int, tile_rows,
+				  AV1_MAX_TILES / tile_cols);
+	}
+
+	context_update_y = tile_info->context_update_tile_id / tile_cols;
+	context_update_x = tile_info->context_update_tile_id % tile_cols;
+	context_update_tile_id = context_update_x * tile_rows + context_update_y;
+
 	memset(dst, 0, av1_dec->tile_info.size);
 
-	for (tile0 = 0; tile0 < tile_info->tile_cols; tile0++) {
-		for (tile1 = 0; tile1 < tile_info->tile_rows; tile1++) {
-			int tile_id = tile1 * tile_info->tile_cols + tile0;
+	for (tile0 = 0; tile0 < tile_cols; tile0++) {
+		for (tile1 = 0; tile1 < tile_rows; tile1++) {
+			int tile_id = tile1 * tile_cols + tile0;
 			u32 start, end;
 			u32 y0 =
 			    tile_info->height_in_sbs_minus_1[tile1] + 1;
-- 
2.53.0