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

Konrad Rzeszutek Wilk
2019-06-10T15:47:19Z

On Mon, Jun 03, 2019 at 09:16:14AM +0800, Lu Baolu wrote:
> This is necessary to avoid exposing valid kernel data to any
> milicious device.

malicious

>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
> 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);

What if the alloc_size is less than a PAGE? Should this at least have ALIGN or such?

> +
> 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
>