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

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Date:   Mon, 14 Jun 2021 13:38:51 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
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: [PATCH] KVM: svm: Avoid NULL pointer dereference in svm_hv_update_vp_id()

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);
 	}
 }
-- 
2.31.1