linux-kernel - Re: [PATCH] KVM: svm: Avoid NULL pointer dereference in svm_hv_update_vp

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Date:   Mon, 14 Jun 2021 15:31:51 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: svm: Avoid NULL pointer dereference in
 svm_hv_update_vp_id()

On 14/06/21 13:38, Vitaly Kuznetsov wrote:
> Hyper-V context is allocated dynamically when Hyper-V features are enabled
> on a vCPU but svm_hv_update_vp_id() is called unconditionally from
> svm_vcpu_run(), this leads to dereferencing to_hv_vcpu(vcpu) which can
> be NULL. Use kvm_hv_get_vpindex() wrapper to avoid the problem.
> 
> Fixes: 4ba0d72aaa32 ("KVM: SVM: hyper-v: Direct Virtual Flush support")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
> - The patch introducing the issue is currently in kvm/queue.
> ---
>   arch/x86/kvm/svm/svm_onhyperv.h | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm_onhyperv.h b/arch/x86/kvm/svm/svm_onhyperv.h
> index ce23149670ea..9b9a55abc29f 100644
> --- a/arch/x86/kvm/svm/svm_onhyperv.h
> +++ b/arch/x86/kvm/svm/svm_onhyperv.h
> @@ -99,9 +99,10 @@ static inline void svm_hv_update_vp_id(struct vmcb *vmcb,
>   {
>   	struct hv_enlightenments *hve =
>   		(struct hv_enlightenments *)vmcb->control.reserved_sw;
> +	u32 vp_index = kvm_hv_get_vpindex(vcpu);
>   
> -	if (hve->hv_vp_id != to_hv_vcpu(vcpu)->vp_index) {
> -		hve->hv_vp_id = to_hv_vcpu(vcpu)->vp_index;
> +	if (hve->hv_vp_id != vp_index) {
> +		hve->hv_vp_id = vp_index;
>   		vmcb_mark_dirty(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);
>   	}
>   }
> 

Squashed, thanks.

Paolo