linux-kernel - Re: [PATCH] KVM: x86: remove dead initialization

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Message-ID: <YRFgb5AbeL8fprgc@google.com>
Date:   Mon, 9 Aug 2021 17:05:51 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] KVM: x86: remove dead initialization

On Mon, Aug 09, 2021, Paolo Bonzini wrote:
> hv_vcpu is initialized again a dozen lines below, so remove the
> initializer.

Eewwww.  It's not just dead code, it's code that could potentially lead to
dereferncing a NULL pointer and/or a stale pointer.  The second initialization
of the local hv_vcpu happens after a conditional call to kvm_hv_vcpu_init().

Maybe update the changelog to clarify why the second initialization absolutely
must be kept?

For the code:

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/hyperv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index e9582db29a99..2da21e45da99 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1968,7 +1968,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
>  void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpuid_entry2 *entry;
> -	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> +	struct kvm_vcpu_hv *hv_vcpu;
>  
>  	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_INTERFACE, 0);
>  	if (entry && entry->eax == HYPERV_CPUID_SIGNATURE_EAX) {
> -- 
> 2.27.0
>