linux-kernel - Re: [PATCH] KVM: x86: fix wbinvd_dirty

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Message-ID: <5488ed61-ac8b-c067-3508-d6832367e4ea@redhat.com>
Date:   Mon, 24 Oct 2016 16:15:51 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ido Yariv <ido@...ery.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: fix wbinvd_dirty_mask use-after-free



On 21/10/2016 18:39, Ido Yariv wrote:
> vcpu->arch.wbinvd_dirty_mask may still be used after freeing it,
> corrupting memory. For example, the following call trace may set a bit
> in an already freed cpu mask:
>     kvm_arch_vcpu_load
>     vcpu_load
>     vmx_free_vcpu_nested
>     vmx_free_vcpu
>     kvm_arch_vcpu_free
> 
> Fix this by deferring freeing of wbinvd_dirty_mask.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Ido Yariv <ido@...ery.com>
> ---
>  arch/x86/kvm/x86.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 6c633de..9ec8c1d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7410,10 +7410,12 @@ void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
>  
>  void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
>  {
> +	void *wbinvd_dirty_mask = vcpu->arch.wbinvd_dirty_mask;
> +
>  	kvmclock_reset(vcpu);
>  
> -	free_cpumask_var(vcpu->arch.wbinvd_dirty_mask);
>  	kvm_x86_ops->vcpu_free(vcpu);
> +	free_cpumask_var(wbinvd_dirty_mask);
>  }
>  
>  struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
> 

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>