linux-kernel - Re: [PATCH MANUALSEL 5.14 5/9] KVM: x86: VMX: synthesize invalid VM exit when emulating invalid guest state

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Date:   Wed, 6 Oct 2021 15:35:37 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH MANUALSEL 5.14 5/9] KVM: x86: VMX: synthesize invalid VM
 exit when emulating invalid guest state

On 06/10/21 15:30, Sasha Levin wrote:
> From: Maxim Levitsky <mlevitsk@...hat.com>
> 
> [ Upstream commit c42dec148b3e1a88835e275b675e5155f99abd43 ]
> 
> Since no actual VM entry happened, the VM exit information is stale.
> To avoid this, synthesize an invalid VM guest state VM exit.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> Message-Id: <20210913140954.165665-6-mlevitsk@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>   arch/x86/kvm/vmx/vmx.c | 17 ++++++++++++++---
>   1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 256f8cab4b8b..339116ff236f 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6607,10 +6607,21 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
>   		     vmx->loaded_vmcs->soft_vnmi_blocked))
>   		vmx->loaded_vmcs->entry_time = ktime_get();
>   
> -	/* Don't enter VMX if guest state is invalid, let the exit handler
> -	   start emulation until we arrive back to a valid state */
> -	if (vmx->emulation_required)
> +	/*
> +	 * Don't enter VMX if guest state is invalid, let the exit handler
> +	 * start emulation until we arrive back to a valid state.  Synthesize a
> +	 * consistency check VM-Exit due to invalid guest state and bail.
> +	 */
> +	if (unlikely(vmx->emulation_required)) {
> +		vmx->fail = 0;
> +		vmx->exit_reason.full = EXIT_REASON_INVALID_STATE;
> +		vmx->exit_reason.failed_vmentry = 1;
> +		kvm_register_mark_available(vcpu, VCPU_EXREG_EXIT_INFO_1);
> +		vmx->exit_qualification = ENTRY_FAIL_DEFAULT;
> +		kvm_register_mark_available(vcpu, VCPU_EXREG_EXIT_INFO_2);
> +		vmx->exit_intr_info = 0;
>   		return EXIT_FASTPATH_NONE;
> +	}
>   
>   	trace_kvm_entry(vcpu);
>   
> 

NACK