[PATCH v3 6/9] media: verisilicon: rockchip: guard VPU981 AV1 divisor and tile buffer

[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, which holds AV1_MAX_TILES entries; tile_cols and tile_rows
come from the bitstream. Guard the division against a zero tile_cols by
initialising the context-update values to zero and computing them only
when tile_cols is non-zero, and stop the descriptor writes once the
tile_info buffer is full. The tile geometry written to the hardware
registers is left unmodified; the per-dimension and total tile bounds are
enforced by the control validation.

Fixes: 727a400686a2 ("media: verisilicon: Add Rockchip AV1 decoder")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 .../verisilicon/rockchip_vpu981_hw_av1_dec.c  | 32 +++++++++++++++----
 1 file changed, 26 insertions(+), 6 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..fd00dbd79fe46 100644
--- a/drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c
+++ b/drivers/media/platform/verisilicon/rockchip_vpu981_hw_av1_dec.c
@@ -578,16 +578,30 @@ 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;
+	int context_update_y = 0;
+	int context_update_x = 0;
+	int context_update_tile_id = 0;
 	u8 *dst = av1_dec->tile_info.cpu;
+	u8 *dst_end = dst + av1_dec->tile_info.size;
 	struct hantro_dev *vpu = ctx->dev;
 	int tile0, tile1;
 
+	/*
+	 * tile_cols and tile_rows are bounded by the V4L2 control validation
+	 * (V4L2_AV1_MAX_TILE_{COLS,ROWS} and V4L2_AV1_MAX_TILE_COUNT). Guard
+	 * the divisor here, and keep the descriptor writes within the
+	 * AV1_MAX_TILES tile_info buffer below; the register values use the
+	 * unmodified tile geometry.
+	 */
+	if (tile_info->tile_cols) {
+		context_update_y =
+		    tile_info->context_update_tile_id / tile_info->tile_cols;
+		context_update_x =
+		    tile_info->context_update_tile_id % tile_info->tile_cols;
+		context_update_tile_id =
+		    context_update_x * tile_info->tile_rows + context_update_y;
+	}
+
 	memset(dst, 0, av1_dec->tile_info.size);
 
 	for (tile0 = 0; tile0 < tile_info->tile_cols; tile0++) {
@@ -598,6 +612,10 @@ static void rockchip_vpu981_av1_dec_set_tile_info(struct hantro_ctx *ctx)
 			    tile_info->height_in_sbs_minus_1[tile1] + 1;
 			u32 x0 = tile_info->width_in_sbs_minus_1[tile0] + 1;
 
+			/* Stop once the tile_info descriptor buffer is full. */
+			if (dst + 16 > dst_end)
+				break;
+
 			/* tile size in SB units (width,height) */
 			*dst++ = x0;
 			*dst++ = 0;
@@ -622,6 +640,8 @@ static void rockchip_vpu981_av1_dec_set_tile_info(struct hantro_ctx *ctx)
 			*dst++ = (end >> 16) & 255;
 			*dst++ = (end >> 24) & 255;
 		}
+		if (dst + 16 > dst_end)
+			break;
 	}
 
 	hantro_reg_write(vpu, &av1_multicore_expect_context_update, !!(context_update_x == 0));
-- 
2.53.0