Re: [PATCH] docs: security: Confidential computing intro and threat model

[Carlos Bilbao <carlos.bilbao@amd.com>]

On 4/26/23 10:51 AM, Sean Christopherson wrote:
> On Wed, Apr 26, 2023, Carlos Bilbao wrote:
>> Hello Sean,
>>
>> On 4/26/23 8:32 AM, Reshetova, Elena wrote:
>>>  Hi Sean, 
>>>
>>> Thank you for your review! Please see my comments inline. 
>>>
>>>> On Mon, Mar 27, 2023, Carlos Bilbao wrote:
> 
> ...
> 
>>>>> More details on the x86-specific solutions can be
>>>>> +found in
>>>>> +:doc:`Intel Trust Domain Extensions (TDX) </x86/tdx>` and
>>>>> +:doc:`AMD Memory Encryption </x86/amd-memory-encryption>`.
>>>>
>>>> So by the above definition, vanilla SEV and SEV-ES can't be considered CoCo.  SEV
>>>> doesn't provide anything besides increased confidentiality of guest memory, and
>>>> SEV-ES doesn't provide integrity or validation of physical page assignment.
>>>>
>>>
>>> Same
>>>
>>
>> Personally, I think it's reasonable to mention SEV/SEV-ES in the context of
>> confidential computing and acknowledge their relevance in this area.
>>
>> But there is no mention to SEV or SEV-ES in this draft. And the document we
>> reference there covers AMD-SNP, which provides integrity.
> 
> ...
> 
>>>>> +While the traditional hypervisor has unlimited access to guest data and
>>>>> +can leverage this access to attack the guest, the CoCo systems mitigate
>>>>> +such attacks by adding security features like guest data confidentiality
>>>>> +and integrity protection. This threat model assumes that those features
>>>>> +are available and intact.
>>>>
>>>> Again, if you're claiming integrity is a key tenant, then SEV and SEV-ES can't be
>>>> considered CoCo.
>>
>> Again, nobody mentioned SEV/SEV-ES here.
> 
> Yes, somebody did.  Unless your dictionary has a wildly different definition for
> "all".
> 
>  : +Overview and terminology
>  : +========================
>  : +
>  : +Confidential Cloud Computing (CoCo) refers to a set of HW and SW
>  : +virtualization technologies that allow Cloud Service Providers (CSPs) to
>  : +provide stronger security guarantees to their clients (usually referred to
>  : +as tenants) by excluding all the CSP's infrastructure and SW out of the
>  : +tenant's Trusted Computing Base (TCB).
>  : +
>  : +While the concrete implementation details differ between technologies, all
>                                                                            ^^^
>  : +of these mechanisms provide increased confidentiality and integrity of CoCo
>  : +guest memory and execution state (vCPU registers), more tightly controlled
>  : +guest interrupt injection, as well as some additional mechanisms to control
>  : +guest-host page mapping. More details on the x86-specific solutions can be
>  : +found in
> 
> This document is named confidential-computing.rst, not tdx-and-snp.rst.  Not
> explicitly mentioning SEV doesn't magically warp reality to make descriptions like
> this one from security/secrets/coco.rst disappear:
> 
>   Introduction                                                                    
>   ============                                                                    
>                                                                                 
>   Confidential Computing (coco) hardware such as AMD SEV (Secure Encrypted        
>   Virtualization) allows guest owners to inject secrets into the VMs              
>   memory without the host/hypervisor being able to read them.
> 
> My complaint about this document being too Intel/AMD centric isn't that it doesn't
> mention other implementations, it's that the doc describes CoCo purely from the
> narrow viewpoint of Intel TDX and AMD SNP, and to be blunt, reads like a press
> release and not an objective overview of CoCo.

Be specific about the parts of the document that you feel are too
AMD/Intel centric, and we will correct them.

Thanks,
Carlos