[PATCH v4 3/9] swiotlb: Zero out bounce buffer for untrusted device

[Lu Baolu]

This is necessary to avoid exposing valid kernel data to any
milicious device.

Suggested-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 kernel/dma/swiotlb.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index f956f785645a..ed41eb7f6131 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -35,6 +35,7 @@
 #include <linux/scatterlist.h>
 #include <linux/mem_encrypt.h>
 #include <linux/set_memory.h>
+#include <linux/pci.h>
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 #endif
@@ -560,6 +561,11 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 	 */
 	for (i = 0; i < nslots; i++)
 		io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
+
+	/* Zero out the bounce buffer if the consumer is untrusted. */
+	if (dev_is_untrusted(hwdev))
+		memset(phys_to_virt(tlb_addr), 0, alloc_size);
+
 	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
 	    (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
 		swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);
-- 
2.17.1