linux-kernel - Re: [PATCH v2] docs: security: Confidential computing intro and threat model for x86 virtualization

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Date:   Mon, 19 Jun 2023 17:03:35 +0200
From:   Dmytro Maluka <dmy@...ihalf.com>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
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Subject: Re: [PATCH v2] docs: security: Confidential computing intro and
 threat model for x86 virtualization

On 6/19/23 13:23, Reshetova, Elena wrote:
>> And BTW, doesn't it mean that interrupts also need to be hardened in the
>> guest (if we don't want the complexity of interrupt controllers in the
>> trusted hypervisor)? At least sensitive ones like IPIs, but I guess we
>> should also consider interrupt-based timings attacks, which could use
>> any type of interrupt. (I have no idea how to harden either of the two
>> cases, but I'm no expert.)
> 
> We have been thinking about it a bit at least when it comes to our
> TDX case. Two main issues were identified: interrupts contributing
> to the state of Linux PRNG [1] and potential implications of missing
> interrupts for reliable panic and other kernel use cases [2]. 
> 
> [1] https://intel.github.io/ccc-linux-guest-hardening-docs/security-spec.html#randomness-inside-tdx-guest
> [2] https://intel.github.io/ccc-linux-guest-hardening-docs/security-spec.html#reliable-panic
> 
> For the first one, in addition to simply enforce usage of RDSEED
> for TDX guests, we still want to do a proper evaluation of security
> of Linux PRNG under our threat model. The second one is 
> harder to reliably asses imo, but so far we were not able to find any
> concrete attack vectors. But it would be good if people who 
> have expertise in this, could take a look on the assessment we did. 
> The logic was to go over all kernel core callers of various 
> smp_call_function*, on_each_cpu* and check the implications
> if such an IPI is never delivered. 

Thanks. I also had in mind for example [1].

[1] https://people.cs.kuleuven.be/~jo.vanbulck/ccs18.pdf