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

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Message-ID: <20190610154553.GT28796@char.us.oracle.com>
Date:   Mon, 10 Jun 2019 11:45:53 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Christoph Hellwig <hch@....de>, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, alan.cox@...el.com, kevin.tian@...el.com,
        mika.westerberg@...ux.intel.com, Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        pengfei.xu@...el.com, Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Jonathan Corbet <corbet@....net>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/9] swiotlb: Zero out bounce buffer for untrusted
 device

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@....de>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.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
>