[PATCH 4/4] KVM: x86: forcibly leave nested mode on vCPU reset

[Maxim Levitsky]

While not obivous, kvm_vcpu_reset leaves the nested mode by
clearing 'vcpu->arch.hflags' but it does so without all the
required housekeeping.

This makes SVM and VMX continue to use vmcs02/vmcb02 while
the cpu is not in nested mode.

In particular, in SVM code, it makes the 'svm_free_nested'
free the vmcb02, while still in use, which later triggers
use after free and a kernel crash.

This issue is assigned CVE-2022-3344

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d86a8aae1471d3..313c4a6dc65e45 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11931,6 +11931,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	WARN_ON_ONCE(!init_event &&
 		     (old_cr0 || kvm_read_cr3(vcpu) || kvm_read_cr4(vcpu)));
 
+	kvm_leave_nested(vcpu);
 	kvm_lapic_reset(vcpu, init_event);
 
 	vcpu->arch.hflags = 0;
-- 
2.26.3