mtd: gpmi: add sanity check when mapping DMA for read_buf/write_buf

The buffer pointer passed from the upper layer may points to
a buffer in the stack or a buffer allocated by vmalloc, and etc..

This patch adds more sanity check to this buffer.
After this patch, if we meet a buffer which is allocated by vmalloc or
a buffer in the stack, we will use our own DMA buffer @data_buffer_dma
to do the DMA operations. If the buffer is not the cases above, we will
map it for DMA operations directly.
Signed-off-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/gpmi-nand/gpmi-nand.c

@@ -367,25 +367,28 @@ void prepare_data_dma(struct gpmi_nand_data *this, enum dma_data_direction dr)
 	struct scatterlist *sgl = &this->data_sgl;
 	int ret;
 
-	this->direct_dma_map_ok = true;
-
 	/* first try to map the upper buffer directly */
+	if (virt_addr_valid(this->upper_buf) &&
+		!object_is_on_stack(this->upper_buf)) {
 		sg_init_one(sgl, this->upper_buf, this->upper_len);
 		ret = dma_map_sg(this->dev, sgl, 1, dr);
-	if (ret == 0) {
+		if (ret == 0)
+			goto map_fail;
+
+		this->direct_dma_map_ok = true;
+		return;
+	}
+
+map_fail:
 	/* We have to use our own DMA buffer. */
-		sg_init_one(sgl, this->data_buffer_dma, PAGE_SIZE);
+	sg_init_one(sgl, this->data_buffer_dma, this->upper_len);
 
 	if (dr == DMA_TO_DEVICE)
-			memcpy(this->data_buffer_dma, this->upper_buf,
-				this->upper_len);
+		memcpy(this->data_buffer_dma, this->upper_buf, this->upper_len);
 
-		ret = dma_map_sg(this->dev, sgl, 1, dr);
-		if (ret == 0)
-			dev_err(this->dev, "DMA mapping failed.\n");
+	dma_map_sg(this->dev, sgl, 1, dr);
 
 	this->direct_dma_map_ok = false;
-	}
 }
 
 /* This will be called after the DMA operation is finished. */