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

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

[Sean Christopherson]

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@syzkaller.appspotmail.com
Signed-off-by: Sean Christopherson <seanjc@google.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
-- 
2.36.0.464.gb9c8b46e94-goog

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

[Paolo Bonzini]

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@syzkaller.appspotmail.com
> Signed-off-by: Sean Christopherson <seanjc@google.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