[PATCH v2 3/3] KVM: SVM: Remove VM from the GA Log notifier list before VM destruction

[Sean Christopherson]

When a VM is being destroyed, delete it from the list used to process GA
Log interrupts before vCPUs are freed, otherwise avic_ga_log_notifier()
could theoretically hit a use-after-free if a GA Log notification arrives
for a vCPU after the last reference to the VM has been put.

Note, in practice, it's likely all but impossible to trigger UAF, as all
all irqfds and thus all IRTEs are cleaned up by:

  kvm_irqfd_release()
  |
  |-> irqfd_deactivate()
      |
      |-> irqfd_shutdown()
          |
          |-> irq_bypass_unregister_consumer()

And kvm_irqfd_release() is guaranteed to run before the last reference to
the VM is put.  KVM also configures GA Log interrupts only when a vCPU is
blocking (older versions of KVM configre GA Log interrupts at all times,
but AVIC is off by default on those kernels).  Hitting UAF would require
tearing down a VM shortly after a vCPU stopped blocking, and with a very,
very delayed IRQ from hardware.

Opportunistically use guard() to avoid a local "flags" variable.

Fixes: 5881f73757cc ("svm: Introduce AMD IOMMU avic_ga_log_notifier")
Cc: Naveen N Rao (AMD) <naveen@xxxxxxxxxx>
Cc: Xiao Wu <xiaowu.417@xxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/svm/avic.c | 19 ++++++++++++-------
 arch/x86/kvm/svm/svm.c  |  2 ++
 arch/x86/kvm/svm/svm.h  |  1 +
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index d71a2fed1a08..c5b1d294b15a 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -374,9 +374,20 @@ int avic_vcpu_precreate(struct kvm *kvm)
 	return 0;
 }
 
+void avic_vm_pre_destroy(struct kvm *kvm)
+{
+	struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
+
+	if (WARN_ON_ONCE(!enable_apicv) || !kvm_svm->avic_vm_id)
+		return;
+
+	guard(spinlock_irqsave)(&svm_vm_data_hash_lock);
+
+	hash_del(&kvm_svm->hnode);
+}
+
 void avic_vm_destroy(struct kvm *kvm)
 {
-	unsigned long flags;
 	struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
 
 	if (!enable_apicv)
@@ -385,12 +396,6 @@ void avic_vm_destroy(struct kvm *kvm)
 	free_page((unsigned long)kvm_svm->avic_logical_id_table);
 	free_pages((unsigned long)kvm_svm->avic_physical_id_table,
 		   avic_get_physical_id_table_order(kvm));
-
-	if (kvm_svm->avic_vm_id) {
-		spin_lock_irqsave(&svm_vm_data_hash_lock, flags);
-		hash_del(&kvm_svm->hnode);
-		spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
-	}
 }
 
 static phys_addr_t avic_get_backing_page_address(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7f3a815d737f..0e0dd9618750 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5329,6 +5329,7 @@ struct kvm_x86_ops svm_x86_ops __initdata = {
 
 	.vm_size = sizeof(struct kvm_svm),
 	.vm_init = svm_vm_init,
+	.vm_pre_destroy = avic_vm_pre_destroy,
 	.vm_destroy = svm_vm_destroy,
 
 	.prepare_switch_to_guest = svm_prepare_switch_to_guest,
@@ -5702,6 +5703,7 @@ static __init int svm_hardware_setup(void)
 	if (!enable_apicv) {
 		enable_ipiv = false;
 		svm_x86_ops.vcpu_precreate = NULL;
+		svm_x86_ops.vm_pre_destroy = NULL;
 		svm_x86_ops.vcpu_blocking = NULL;
 		svm_x86_ops.vcpu_unblocking = NULL;
 		svm_x86_ops.vcpu_get_apicv_inhibit_reasons = NULL;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 3c5459374969..616e45624f4c 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -946,6 +946,7 @@ extern struct kvm_x86_nested_ops svm_nested_ops;
 bool __init avic_hardware_setup(void);
 void avic_hardware_unsetup(void);
 int avic_vcpu_precreate(struct kvm *kvm);
+void avic_vm_pre_destroy(struct kvm *kvm);
 void avic_vm_destroy(struct kvm *kvm);
 int avic_vm_init(struct kvm *kvm);
 void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb);
-- 
2.55.0.rc0.799.gd6f94ed593-goog