linux-kernel - Re: [PATCH v2 5/6] KVM: x86: prevent setup of invalid routes

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Date:   Tue, 10 Jan 2017 10:43:14 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Xu <peterx@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 5/6] KVM: x86: prevent setup of invalid routes



On 10/01/2017 06:26, Peter Xu wrote:
> On Fri, Dec 16, 2016 at 04:10:05PM +0100, Radim Krčmář wrote:
>> The check in kvm_set_pic_irq() and kvm_set_ioapic_irq() was just a
>> temporary measure until the code improved enough for us to do this.
>>
>> This changes APIC in a case when KVM_SET_GSI_ROUTING is called to set up pic
>> and ioapic routes before KVM_CREATE_IRQCHIP.  Those rules would get overwritten
>> by KVM_CREATE_IRQCHIP at best, so it is pointless to allow it.  Userspaces
>> hopefully noticed that things don't work if they do that and don't do that.
>>
>> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
>> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> 
> Since we are at here, do we need to protect KVM_SET_GSI_ROUTING in
> general as well to make sure kernel APIC is there?

Skipping the check is harmless.  I agree that it should have been always
done like you suggest, but right now it may break something.

Paolo

> 
> ---------8<---------
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 482612b..31141a7 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3057,6 +3057,10 @@ static long kvm_vm_ioctl(struct file *filp,
>                 struct kvm_irq_routing_entry *entries = NULL;
> 
>                 r = -EFAULT;
> +
> +               if (!irqchip_in_kernel(kvm))
> +                       goto out;
> +
>                 if (copy_from_user(&routing, argp, sizeof(routing)))
>                         goto out;
>                 r = -EINVAL;
> 
> --------->8---------
> 
> Thanks,
> 
> -- peterx
>