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

[Sean Christopherson <seanjc@google.com>]

On Fri, Sep 03, 2021, tcs.kernel@gmail.com wrote:
> 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>

Neither myself nor Vitaly provided an SOB, nor is one needed.  Review feedback
can be attributed/noted in the part that git ignores (below the three dashes).

> Reported-by: TCS Robot <tcs_robot@tencent.com>
> 
> ---

Notes about version changes, e.g. to document/attribute review feedback, go here.

  v2: 
    - Blah blah blah [Vitaly, Sean]

>  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/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;

Before moving forward with a fix, I'd like to get Paolo's input on dropping
track_srcu in favor of kvm->srcu and avoiding this altogheter.  Note, Paolo is on
vacation at the moment, so this won't get attention for a week or more.

[*] https://lkml.kernel.org/r/YS5Bn6I6wVEL8wKS@google.com

>  	kvm_mmu_init_vm(kvm);
>  	kvm_xen_init_vm(kvm);
>  
> -- 
> 1.8.3.1
>