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

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Message-ID: <b6229f0e-fee1-6623-f6c9-3648e18b2500@linux.intel.com>
Date:   Thu, 30 Sep 2021 12:40:48 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Andi Kleen <ak@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Jason Wang <jasowang@...hat.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        "Reshetova, Elena" <elena.reshetova@...el.com>
Subject: Re: [PATCH v2 4/6] virtio: Initialize authorized attribute for
 confidential guest

+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