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Message-ID: <20240816130124.286226-1-vkuznets@redhat.com>
Date: Fri, 16 Aug 2024 15:01:24 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: kvm@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>
Cc: Mirsad Todorovac <mtodorovac69@...il.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: VMX: hyper-v: Prevent impossible NULL pointer dereference in evmcs_load()
GCC 12.3.0 complains about a potential NULL pointer dereference in
evmcs_load() as hv_get_vp_assist_page() can return NULL. In fact, this
cannot happen because KVM verifies (hv_init_evmcs()) that every CPU has a
valid VP assist page and aborts enabling the feature otherwise. CPU
onlining path is also checked in vmx_hardware_enable().
To make the compiler happy and to future proof the code, add a KVM_BUG_ON()
sentinel. It doesn't seem to be possible (and logical) to observe
evmcs_load() happening without an active vCPU so it is presumed that
kvm_get_running_vcpu() can't return NULL.
No functional change intended.
Reported-by: Mirsad Todorovac <mtodorovac69@...il.com>
Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
arch/x86/kvm/vmx/vmx_onhyperv.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kvm/vmx/vmx_onhyperv.h b/arch/x86/kvm/vmx/vmx_onhyperv.h
index eb48153bfd73..bba24ed99ee6 100644
--- a/arch/x86/kvm/vmx/vmx_onhyperv.h
+++ b/arch/x86/kvm/vmx/vmx_onhyperv.h
@@ -104,6 +104,14 @@ static inline void evmcs_load(u64 phys_addr)
struct hv_vp_assist_page *vp_ap =
hv_get_vp_assist_page(smp_processor_id());
+ /*
+ * When enabling eVMCS, KVM verifies that every CPU has a valid hv_vp_assist_page()
+ * and aborts enabling the feature otherwise. CPU onlining path is also checked in
+ * vmx_hardware_enable().
+ */
+ if (KVM_BUG_ON(!vp_ap, kvm_get_running_vcpu()->kvm))
+ return;
+
if (current_evmcs->hv_enlightenments_control.nested_flush_hypercall)
vp_ap->nested_control.features.directhypercall = 1;
vp_ap->current_nested_vmcs = phys_addr;
--
2.46.0
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