Virtualization - Jun 2021 - [PATCH v1 1/8] virtio: Force only split mode with protected guest

? 2021/6/3 ??10:56, Andi Kleen ??:
>
>>
>> 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

> 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?
I don't. If you can validate everything it's probably ok

The only drawback is even more code to audit and test.

-Andi