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

From: tcs . kernel
Date: Thu Sep 02 2021 - 22:37:24 EST


From: Haimin Zhang <tcs_kernel@xxxxxxxxxxx>

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@xxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Reported-by: TCS Robot <tcs_robot@xxxxxxxxxxx>

---
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