From: Paolo Bonzini <pbonzini@redhat.com>
Date: Fri, 19 Jul 2019 18:41:10 +0200
Subject: KVM: nVMX: do not use dangling shadow VMCS after guest reset
Git-commit: 88dddc11a8d6b09201b4db9d255b3394d9bc9e57
Patch-mainline: v5.3-rc1
References: bsc#1145390

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>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kvm/vmx/nested.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7661,6 +7661,7 @@ 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.sync_shadow_vmcs = false;
 }
 
 static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
@@ -7672,7 +7673,6 @@ static inline void nested_release_vmcs12
 		/* copy to memory all shadowed fields in case
 		   they were modified */
 		copy_shadow_to_vmcs12(vmx);
-		vmx->nested.sync_shadow_vmcs = false;
 		vmx_disable_shadow_vmcs(vmx);
 	}
 	vmx->nested.posted_intr_nv = -1;
@@ -7859,6 +7859,9 @@ static void copy_shadow_to_vmcs12(struct
 	const unsigned long *fields = shadow_read_write_fields;
 	const int num_fields = max_shadow_read_write_fields;
 
+	if (WARN_ON(!shadow_vmcs))
+		return;
+
 	preempt_disable();
 
 	vmcs_load(shadow_vmcs);
@@ -7906,6 +7909,9 @@ 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++) {