2 files changed, 50 insertions, 4 deletions

diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index 4f8224a6ac95..4e16c71c24b7 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY
 	  This is marked experimental because we don't yet have a consistent
 	  execution context and memory management between drivers.
 
+config DMABUF_DEBUG
+	bool "DMA-BUF debug checks"
+	default y if DMA_API_DEBUG
+	help
+	  This option enables additional checks for DMA-BUF importers and
+	  exporters. Specifically it validates that importers do not peek at the
+	  underlying struct page when they import a buffer.
+
 config DMABUF_SELFTESTS
 	tristate "Selftests for the dma-buf interfaces"
 	default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index b8465243eca2..3948b88aa123 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -653,6 +653,34 @@ void dma_buf_put(struct dma_buf *dmabuf)
 }
 EXPORT_SYMBOL_GPL(dma_buf_put);
 
+static void mangle_sg_table(struct sg_table *sg_table)
+{
+#ifdef CONFIG_DMABUF_DEBUG
+	int i;
+	struct scatterlist *sg;
+
+	/* To catch abuse of the underlying struct page by importers mix
+	 * up the bits, but take care to preserve the low SG_ bits to
+	 * not corrupt the sgt. The mixing is undone in __unmap_dma_buf
+	 * before passing the sgt back to the exporter. */
+	for_each_sgtable_sg(sg_table, sg, i)
+		sg->page_link ^= ~0xffUL;
+#endif
+
+}
+static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
+				       enum dma_data_direction direction)
+{
+	struct sg_table *sg_table;
+
+	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+
+	if (!IS_ERR_OR_NULL(sg_table))
+		mangle_sg_table(sg_table);
+
+	return sg_table;
+}
+
 /**
  * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
  * @dmabuf:		[in]	buffer to attach device to.
@@ -724,7 +752,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
 				goto err_unlock;
 		}
 
-		sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
+		sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL);
 		if (!sgt)
 			sgt = ERR_PTR(-ENOMEM);
 		if (IS_ERR(sgt)) {
@@ -771,6 +799,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
 }
 EXPORT_SYMBOL_GPL(dma_buf_attach);
 
+static void __unmap_dma_buf(struct dma_buf_attachment *attach,
+			    struct sg_table *sg_table,
+			    enum dma_data_direction direction)
+{
+	/* uses XOR, hence this unmangles */
+	mangle_sg_table(sg_table);
+
+	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+}
+
 /**
  * dma_buf_detach - Remove the given attachment from dmabuf's attachments list
  * @dmabuf:	[in]	buffer to detach from.
@@ -789,7 +827,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
 		if (dma_buf_is_dynamic(attach->dmabuf))
 			dma_resv_lock(attach->dmabuf->resv, NULL);
 
-		dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
+		__unmap_dma_buf(attach, attach->sgt, attach->dir);
 
 		if (dma_buf_is_dynamic(attach->dmabuf)) {
 			dma_buf_unpin(attach);
@@ -911,7 +949,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
 		}
 	}
 
-	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+	sg_table = __map_dma_buf(attach, direction);
 	if (!sg_table)
 		sg_table = ERR_PTR(-ENOMEM);
 
@@ -974,7 +1012,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
 	if (dma_buf_is_dynamic(attach->dmabuf))
 		dma_resv_assert_held(attach->dmabuf->resv);
 
-	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+	__unmap_dma_buf(attach, sg_table, direction);
 
 	if (dma_buf_is_dynamic(attach->dmabuf) &&
 	    !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))