[PATCH 3.12 090/144] KVM: nVMX: Unconditionally uninit the MMU on nested vmexit

From: Greg Kroah-Hartman
Date: Mon Jan 06 2014 - 18:54:51 EST

3.12-stable review patch. If anyone has any objections, please let me know.


From: Jan Kiszka <jan.kiszka@xxxxxx>

commit 29bf08f12b2fd72b882da0d85b7385e4a438a297 upstream.

Three reasons for doing this: 1. arch.walk_mmu points to arch.mmu anyway
in case nested EPT wasn't in use. 2. this aligns VMX with SVM. But 3. is
most important: nested_cpu_has_ept(vmcs12) queries the VMCS page, and if
one guest VCPU manipulates the page of another VCPU in L2, we may be
fooled to skip over the nested_ept_uninit_mmu_context, leaving mmu in
nested state. That can crash the host later on if nested_ept_get_cr3 is
invoked while L1 already left vmxon and nested.current_vmcs12 became
NULL therefore.

Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/x86/kvm/vmx.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8218,8 +8218,7 @@ static void load_vmcs12_host_state(struc
vcpu->arch.cr4_guest_owned_bits = ~vmcs_readl(CR4_GUEST_HOST_MASK);
kvm_set_cr4(vcpu, vmcs12->host_cr4);

- if (nested_cpu_has_ept(vmcs12))
- nested_ept_uninit_mmu_context(vcpu);
+ nested_ept_uninit_mmu_context(vcpu);

kvm_set_cr3(vcpu, vmcs12->host_cr3);

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