linux-kernel - Re: [PATCH v1 1/8] virtio: Force only split mode with protected guest

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Date:   Thu, 3 Jun 2021 11:02:21 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Andi Kleen <ak@...ux.intel.com>, mst@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, hch@....de,
        m.szyprowski@...sung.com, robin.murphy@....com,
        iommu@...ts.linux-foundation.org, x86@...nel.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, jpoimboe@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/8] virtio: Force only split mode with protected guest


在 2021/6/3 上午10:56, Andi Kleen 写道:
>
>>
>> I agree, but I want to know why indirect descriptor needs to be 
>> disabled. The table can't be wrote by the device since it's not 
>> coherent swiotlb mapping.
>
> I had all kinds of problems with uninitialized entries in the indirect 
> table. So I gave up on it and concluded it would be too difficult to 
> secure.
>
>
> -Andi
>
>

Ok, but what I meant is this, if we don't read from the descriptor ring, 
and validate all the other metadata supplied by the device (used id and 
len). Then there should be no way for the device to suppress the dma 
flags to write to the indirect descriptor table.

Or do you have an example how it can do that?

Thanks