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Subject: Re: [PATCH] KVM: Remove CREATE_IRQCHIP/SET_PIT2 race
To:     Jon Cargille <jcargill@google.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Steve Rutherford <srutherford@google.com>
References: <20200416191152.259434-1-jcargill@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <f7b8ca30-21fa-5268-7f17-889f10b90187@redhat.com>
Date:   Fri, 17 Apr 2020 17:06:10 +0200
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On 16/04/20 21:11, Jon Cargille wrote:
> From: Steve Rutherford <srutherford@google.com>
> 
> Fixes a NULL pointer dereference, caused by the PIT firing an interrupt
> before the interrupt table has been initialized.
> 
> SET_PIT2 can race with the creation of the IRQchip. In particular,
> if SET_PIT2 is called with a low PIT timer period (after the creation of
> the IOAPIC, but before the instantiation of the irq routes), the PIT can
> fire an interrupt at an uninitialized table.
> 
> Signed-off-by: Steve Rutherford <srutherford@google.com>
> Signed-off-by: Jon Cargille <jcargill@google.com>
> Reviewed-by: Jim Mattson <jmattson@google.com>
> ---
>  arch/x86/kvm/x86.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 027dfd278a973..3cc3f673785c8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5049,10 +5049,13 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  		r = -EFAULT;
>  		if (copy_from_user(&u.ps, argp, sizeof(u.ps)))
>  			goto out;
> +		mutex_lock(&kvm->lock);
>  		r = -ENXIO;
>  		if (!kvm->arch.vpit)
> -			goto out;
> +			goto set_pit_out;
>  		r = kvm_vm_ioctl_set_pit(kvm, &u.ps);
> +set_pit_out:
> +		mutex_unlock(&kvm->lock);
>  		break;
>  	}
>  	case KVM_GET_PIT2: {
> @@ -5072,10 +5075,13 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  		r = -EFAULT;
>  		if (copy_from_user(&u.ps2, argp, sizeof(u.ps2)))
>  			goto out;
> +		mutex_lock(&kvm->lock);
>  		r = -ENXIO;
>  		if (!kvm->arch.vpit)
> -			goto out;
> +			goto set_pit2_out;
>  		r = kvm_vm_ioctl_set_pit2(kvm, &u.ps2);
> +set_pit2_out:
> +		mutex_unlock(&kvm->lock);
>  		break;
>  	}
>  	case KVM_REINJECT_CONTROL: {
> 

Queued, thanks.

Paolo