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Subject[PATCH 5.1 57/62] KVM: nVMX: do not use dangling shadow VMCS after guest reset
Date
From: Paolo Bonzini <pbonzini@redhat.com>

commit 88dddc11a8d6b09201b4db9d255b3394d9bc9e57 upstream.

If a KVM guest is reset while running a nested guest, free_nested will
disable the shadow VMCS execution control in the vmcs01. However,
on the next KVM_RUN vmx_vcpu_run would nevertheless try to sync
the VMCS12 to the shadow VMCS which has since been freed.

This causes a vmptrld of a NULL pointer on my machime, but Jan reports
the host to hang altogether. Let's see how much this trivial patch fixes.

Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/vmx/nested.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -184,6 +184,7 @@ static void vmx_disable_shadow_vmcs(stru
{
vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL, SECONDARY_EXEC_SHADOW_VMCS);
vmcs_write64(VMCS_LINK_POINTER, -1ull);
+ vmx->nested.need_vmcs12_sync = false;
}

static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
@@ -1328,6 +1329,9 @@ static void copy_shadow_to_vmcs12(struct
u64 field_value;
struct vmcs *shadow_vmcs = vmx->vmcs01.shadow_vmcs;

+ if (WARN_ON(!shadow_vmcs))
+ return;
+
preempt_disable();

vmcs_load(shadow_vmcs);
@@ -1366,6 +1370,9 @@ static void copy_vmcs12_to_shadow(struct
u64 field_value = 0;
struct vmcs *shadow_vmcs = vmx->vmcs01.shadow_vmcs;

+ if (WARN_ON(!shadow_vmcs))
+ return;
+
vmcs_load(shadow_vmcs);

for (q = 0; q < ARRAY_SIZE(fields); q++) {
@@ -4336,7 +4343,6 @@ static inline void nested_release_vmcs12
/* copy to memory all shadowed fields in case
they were modified */
copy_shadow_to_vmcs12(vmx);
- vmx->nested.need_vmcs12_sync = false;
vmx_disable_shadow_vmcs(vmx);
}
vmx->nested.posted_intr_nv = -1;

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