[PATCH v8 3/7] swiotlb: Zero out bounce buffer for untrusted device

[Lu Baolu]

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

Suggested-by: Christoph Hellwig <h...@lst.de>
Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
---
 kernel/dma/swiotlb.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 89066efa3840..04bea5a87462 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
@@ -458,6 +459,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
        unsigned long offset_slots;
        unsigned long max_slots;
        unsigned long tmp_io_tlb_used;
+       void *zero_addr;
+       size_t zero_size;
 
        if (no_iotlb_memory)
                panic("Can not allocate SWIOTLB buffer earlier and can't now 
provide you with the DMA bounce buffer");
@@ -565,9 +568,20 @@ 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_addr = phys_to_virt(tlb_addr);
+       zero_size = alloc_size;
+
        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
-           (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
+           (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)) {
                swiotlb_bounce(orig_addr, tlb_addr, mapping_size, 
DMA_TO_DEVICE);
+               zero_addr += mapping_size;
+               zero_size -= mapping_size;
+       }
+
+       /* Zero out the bounce buffer if the consumer is untrusted. */
+       if (dev_is_untrusted(hwdev) && zero_size)
+               memset(zero_addr, 0, zero_size);
 
        return tlb_addr;
 }
-- 
2.17.1