linux-kernel - Re: [PATCH v5 06/10] swiotlb: Zero out bounce buffer for untrusted device

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Date:   Fri, 26 Jul 2019 10:21:36 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Christoph Hellwig <hch@....de>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, 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,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.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 v5 06/10] swiotlb: Zero out bounce buffer for untrusted
 device

Hi,

On 7/25/19 7:49 PM, Christoph Hellwig wrote:
>> index 43c88626a1f3..edc84a00b9f9 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
>> @@ -562,6 +563,11 @@ 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);
> 
> Hmm.  Maybe we need to move the untrusted flag to struct device?
> Directly poking into the pci_dev from swiotlb is a bit of a layering
> violation.

Yes. We can consider this. But I tend to think that it's worth of a
separated series. That's a reason why I defined dev_is_untrusted(). This
helper keeps the caller same when moving the untrusted flag.

> 
>> +
>>   	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);
> 
> Also for the case where we bounce here we only need to zero the padding
> (if there is any), so I think we could optimize this a bit.
> 

Yes. There's duplication here.

Best regards,
Baolu