Add a WARN in free_nested() to ensure vmcs01 is loaded prior to freeing
vmcs02 and friends, and explicitly switch to vmcs01 if it's not. KVM is
supposed to keep is_guest_mode() and loaded_vmcs==vmcs02 synchronized,
but bugs happen and freeing vmcs02 while it's in use will escalate a KVM
error to a use-after-free and potentially crash the kernel.
Do the WARN and switch even in the !vmxon case to help detect latent
bugs. free_nested() is not a hot path, and the check is cheap.
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/vmx/nested.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 03dddf1b6009..3e6cc0d7090e 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -279,6 +279,9 @@ static void free_nested(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
+ if (WARN_ON_ONCE(vmx->loaded_vmcs != &vmx->vmcs01))
+ vmx_switch_vmcs(vcpu, &vmx->vmcs01);
+
if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon)
return;
--
2.28.0
