Re: [PATCH MANUALSEL 4.19 1/2] KVM: x86: Handle SRCU initialization failure during page track init

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 06/10/21 13:12, Sasha Levin wrote:
> From: Haimin Zhang <tcs_kernel@xxxxxxxxxxx>
>
> [ Upstream commit eb7511bf9182292ef1df1082d23039e856d1ddfb ]
>
> 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.
>
> Reported-by: TCS Robot <tcs_robot@xxxxxxxxxxx>
> Signed-off-by: Haimin Zhang <tcs_kernel@xxxxxxxxxxx>
> Message-Id: <1630636626-12262-1-git-send-email-tcs_kernel@xxxxxxxxxxx>
> [Move the call towards the beginning of kvm_arch_init_vm. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>   arch/x86/include/asm/kvm_page_track.h | 2 +-
>   arch/x86/kvm/page_track.c             | 4 ++--
>   arch/x86/kvm/x86.c                    | 7 ++++++-
>   3 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
> index 172f9749dbb2..5986bd4aacd6 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 *free,
> diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
> index 3052a59a3065..1f6b0d9b0c85 100644
> --- a/arch/x86/kvm/page_track.c
> +++ b/arch/x86/kvm/page_track.c
> @@ -169,13 +169,13 @@ 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 417abc9ba1ad..70cb18f89029 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9039,9 +9039,15 @@ void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
>   
>   int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>   {
> +	int ret;
> +
>   	if (type)
>   		return -EINVAL;
>   
> +	ret = kvm_page_track_init(kvm);
> +	if (ret)
> +		return ret;
> +
>   	INIT_HLIST_HEAD(&kvm->arch.mask_notifier_list);
>   	INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
>   	INIT_LIST_HEAD(&kvm->arch.zapped_obsolete_pages);
> @@ -9068,7 +9074,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>   	INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
>   
>   	kvm_hv_init_vm(kvm);
> -	kvm_page_track_init(kvm);
>   	kvm_mmu_init_vm(kvm);
>   
>   	if (kvm_x86_ops->vm_init)

Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>