linux-kernel - Re: [PATCH] KVM: VMX: Exit to userspace if vCPU has injected exception and invalid state

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Message-ID: <ae806798-b98e-c2d8-1926-32fa982a0a50@redhat.com>
Date:   Tue, 3 May 2022 11:35:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+cfafed3bb76d3e37581b@...kaller.appspotmail.com
Subject: Re: [PATCH] KVM: VMX: Exit to userspace if vCPU has injected
 exception and invalid state

On 5/3/22 00:18, Sean Christopherson wrote:
> Exit to userspace with an emulation error if KVM encounters an injected
> exception with invalid guest state, in addition to the existing check of
> bailing if there's a pending exception (KVM doesn't support emulating
> exceptions except when emulating real mode via vm86).
> 
> In theory, KVM should never get to such a situation as KVM is supposed to
> exit to userspace before injecting an exception with invalid guest state.
> But in practice, userspace can intervene and manually inject an exception
> and/or stuff registers to force invalid guest state while a previously
> injected exception is awaiting reinjection.
> 
> Fixes: fc4fad79fc3d ("KVM: VMX: Reject KVM_RUN if emulation is required with pending exception")
> Reported-by: syzbot+cfafed3bb76d3e37581b@...kaller.appspotmail.com
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/vmx/vmx.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index cf8581978bce..c41f0ac700c7 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5465,7 +5465,7 @@ static bool vmx_emulation_required_with_pending_exception(struct kvm_vcpu *vcpu)
>   	struct vcpu_vmx *vmx = to_vmx(vcpu);
>   
>   	return vmx->emulation_required && !vmx->rmode.vm86_active &&
> -	       vcpu->arch.exception.pending;
> +	       (vcpu->arch.exception.pending || vcpu->arch.exception.injected);
>   }
>   
>   static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
> 
> base-commit: 84e5ffd045f33e4fa32370135436d987478d0bf7

Queued, thanks.

Paolo