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SubjectRe: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest
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+Elena

On 9/30/21 12:30 PM, Andi Kleen wrote:
>
> On 9/30/2021 12:04 PM, Kuppuswamy, Sathyanarayanan wrote:
>>
>>
>> On 9/30/21 8:23 AM, Greg Kroah-Hartman wrote:
>>> On Thu, Sep 30, 2021 at 08:18:18AM -0700, Kuppuswamy, Sathyanarayanan wrote:
>>>>
>>>>
>>>> On 9/30/21 6:36 AM, Dan Williams wrote:
>>>>>> And in particular, not all virtio drivers are hardened -
>>>>>> I think at this point blk and scsi drivers have been hardened - so
>>>>>> treating them all the same looks wrong.
>>>>> My understanding was that they have been audited, Sathya?
>>>>
>>>> Yes, AFAIK, it has been audited. Andi also submitted some patches
>>>> related to it. Andi, can you confirm.
>>>
>>> What is the official definition of "audited"?
>>
>>
>> In our case (Confidential Computing platform), the host is an un-trusted
>> entity. So any interaction with host from the drivers will have to be
>> protected against the possible attack from the host. For example, if we
>> are accessing a memory based on index value received from host, we have
>> to make sure it does not lead to out of bound access or when sharing the
>> memory with the host, we need to make sure only the required region is
>> shared with the host and the memory is un-shared after use properly.
>>
>> Elena can share more details, but it was achieved with static analysis
>> and fuzzing. Here is a presentation she is sharing about the work at the
>> Linux Security Summit:
>> https://static.sched.com/hosted_files/lssna2021/b6/LSS-HardeningLinuxGuestForCCC.pdf
>>
>> Andi, can talk more about the specific driver changes that came out of this
>> effort.
>
> The original virtio was quite easy to exploit because it put its free list into the shared ring buffer.
>
> We had a patchkit to harden virtio originally, but after some discussion we instead switched to
> Jason Wang's patchkit to move the virtio metadata into protected memory, which fixed near all of the
> issues. These patches have been already merged. There is one additional patch to limit the virtio
> modes.
>
> There's an ongoing effort to audit (mostly finished I believe) and fuzz the three virtio drivers
> (fuzzing is still ongoing).
>
> There was also a range of changes outside virtio for code outside the device model. Most of it was
> just disabling it though.
>
> -Andi
>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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