Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest

[Kuppuswamy, Sathyanarayanan]

+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