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

From: "Kuppuswamy, Sathyanarayanan"  <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Andi Kleen <ak@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Borislav Petkov <bp@alien8.de>, X86 ML <x86@kernel.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Andreas Noever <andreas.noever@gmail.com>,
	Michael Jamet <michael.jamet@intel.com>,
	Yehezkel Bernat <YehezkelShB@gmail.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Jason Wang <jasowang@redhat.com>,
	Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux PCI <linux-pci@vger.kernel.org>,
	USB list <linux-usb@vger.kernel.org>,
	virtualization@lists.linux-foundation.org, "Reshetova,
	Elena" <elena.reshetova@intel.com>
Subject: Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for confidential guest
Date: Thu, 30 Sep 2021 12:40:48 -0700	[thread overview]
Message-ID: <b6229f0e-fee1-6623-f6c9-3648e18b2500@linux.intel.com> (raw)
In-Reply-To: <291d5e03-ccaa-3a73-cdcd-66cbe80fede1@linux.intel.com>

+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