linux-kernel - Re: [PATCH] KVM: x86: fix uninitialized variable use on KVM_REQ_TRIPLE

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Date:   Wed, 30 Nov 2022 19:35:18 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Dan Carpenter <error27@...il.com>
Subject: Re: [PATCH] KVM: x86: fix uninitialized variable use on
 KVM_REQ_TRIPLE_FAULT

On Wed, 2022-11-30 at 11:15 -0500, Paolo Bonzini wrote:
> If a triple fault was fixed by kvm_x86_ops.nested_ops->triple_fault (by
> turning it into a vmexit), there is no need to leave vcpu_enter_guest().
> Any vcpu->requests will be caught later before the actual vmentry,
> and in fact vcpu_enter_guest() was not initializing the "r" variable.
> Depending on the compiler's whims, this could cause the
> x86_64/triple_fault_event_test test to fail.
> 
> Cc: Maxim Levitsky <mlevitsk@...hat.com>
> Fixes: 92e7d5c83aff ("KVM: x86: allow L1 to not intercept triple fault")
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 246bdc9a9154..7f850dfb4086 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10280,8 +10280,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  				vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
>  				vcpu->mmio_needed = 0;
>  				r = 0;
> +				goto out;
>  			}
> -			goto out;
>  		}
>  		if (kvm_check_request(KVM_REQ_APF_HALT, vcpu)) {
>  			/* Page is swapped out. Do synthetic halt */

I had the same patch waiting to be sent, so:

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>


But we need to add the orignal reporter of this bug as well:

Reported-by: Dan Carpenter <error27@...il.com>

Best regards,
	Maxim Levitsky