linux-kernel - Re: [PATCH v11 7/9] KVM: X86: Add userspace access interface for CET MSRs

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Date:   Mon, 27 Apr 2020 16:04:28 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        sean.j.christopherson@...el.com, jmattson@...gle.com,
        yu.c.zhang@...ux.intel.com
Subject: Re: [PATCH v11 7/9] KVM: X86: Add userspace access interface for CET
 MSRs

On 26/04/20 17:23, Yang Weijiang wrote:
> What's the purpose of the selftest? Is it just for Shadow Stack SSP
> state transitions in various cases? e.g., L0 SSP<--->L3 SSP,
> L0 SSP1<--->L0 SSP2?

No, it checks that the whole state can be extracted and restored from a
running VM.  For example, it would have caught immediately that the
current SSP could not be saved and restored.

> We now have the KVM unit-test for CET functionalities,
> i.e., Shadow Stack and Indirect Branch Tracking for user-mode, I can put the
> state test app into the todo list as current patchset is mainly for user-mode
> protection, the supervisor-mode CET protection is the next step.

What are the limitations?  Or are you referring to the unit test?

Paolo