[PATCH v2] KVM: x86: Handle SRCU initialization failure during page track init

[tcs.kernel@gmail.com]

From: Haimin Zhang <tcs_kernel@tencent.com>

Check the return of init_srcu_struct(), which can fail due to OOM, when
initializing the page track mechanism.  Lack of checking leads to a NULL
pointer deref found by a modified syzkaller.

Signed-off-by: Haimin Zhang <tcs_kernel@tencent.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reported-by: TCS Robot <tcs_robot@tencent.com>

---
 arch/x86/include/asm/kvm_page_track.h | 2 +-
 arch/x86/kvm/mmu/page_track.c         | 4 ++--
 arch/x86/kvm/x86.c                    | 6 +++++-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index 8766adb..9cd9230 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -46,7 +46,7 @@ struct kvm_page_track_notifier_node {
 			    struct kvm_page_track_notifier_node *node);
 };
 
-void kvm_page_track_init(struct kvm *kvm);
+int kvm_page_track_init(struct kvm *kvm);
 void kvm_page_track_cleanup(struct kvm *kvm);
 
 void kvm_page_track_free_memslot(struct kvm_memory_slot *slot);
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index a9e2e02..859800f 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -170,13 +170,13 @@ void kvm_page_track_cleanup(struct kvm *kvm)
 	cleanup_srcu_struct(&head->track_srcu);
 }
 
-void kvm_page_track_init(struct kvm *kvm)
+int kvm_page_track_init(struct kvm *kvm)
 {
 	struct kvm_page_track_notifier_head *head;
 
 	head = &kvm->arch.track_notifier_head;
-	init_srcu_struct(&head->track_srcu);
 	INIT_HLIST_HEAD(&head->track_notifier_list);
+	return init_srcu_struct(&head->track_srcu);
 }
 
 /*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 86539c1..9a122af 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11143,6 +11143,8 @@ void kvm_arch_free_vm(struct kvm *kvm)
 
 int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 {
+	int ret;
+
 	if (type)
 		return -EINVAL;
 
@@ -11178,7 +11180,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 
 	kvm_apicv_init(kvm);
 	kvm_hv_init_vm(kvm);
-	kvm_page_track_init(kvm);
+	ret = kvm_page_track_init(kvm);
+	if (ret)
+		return ret;
 	kvm_mmu_init_vm(kvm);
 	kvm_xen_init_vm(kvm);
 
-- 
1.8.3.1