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

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Message-ID: <ZElOfzn37kmesy7e@google.com>
Date:   Wed, 26 Apr 2023 09:17:03 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     James Bottomley <jejb@...ux.ibm.com>
Cc:     Elena Reshetova <elena.reshetova@...el.com>,
        Carlos Bilbao <carlos.bilbao@....com>,
        "corbet@....net" <corbet@....net>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
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        Rajnesh Kanwal <rkanwal@...osinc.com>,
        Dylan Reid <dylan@...osinc.com>,
        Ravi Sahita <ravi@...osinc.com>
Subject: Re: [PATCH] docs: security: Confidential computing intro and threat model

On Wed, Apr 26, 2023, James Bottomley wrote:
> On Wed, 2023-04-26 at 13:32 +0000, Reshetova, Elena wrote:
> > > On Mon, Mar 27, 2023, Carlos Bilbao wrote:
> [...]
> > > > +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).
> > > 
> > > This is inaccurate, the provider may still have software and/or
> > > hardware in the TCB.
> > 
> > Well, this is the end goal where we want to be,

If by "we" you mean Intel and AMD, then yes, that is probably a true statement.
But those goals have nothing to do with security.

> > the practical deployment can differ of course. We can rephrase that it
> > "allows to exclude all the CSP's infrastructure and SW out of tenant's
> > TCB." 
> 
> That's getting even more inaccurate.  To run  in a Cloud with CoCo you
> usually have to insert some provided code, like OVMF and, for AMD, the
> SVSM.  These are often customized by the CSP to suit the cloud
> infrastructure, so you're running their code.  The goal, I think, is to
> make sure you only run code you trust (some of which may come from the
> CSP) in your TCB, which is very different from the statement above.

Yes.  And taking things a step further, if we were to ask security concious users
what they would choose to have in their TCB: (a) closed-source firmware written by
a hardware vendor, or (b) open-source software that is provided by CSPs, I am
betting the overwhelming majority would choose (b).