Re: [PATCH] KVM: svm: Avoid NULL pointer dereference in svm_hv_update_vp_id()

From: Paolo Bonzini
Date: Mon Jun 14 2021 - 09:32:01 EST


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@xxxxxxxxxx>
---
- 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