linux-kernel - Re: [WRONG] KVM: arm/arm64: vgic: fix off-by-one bug in vgic_get

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Message-ID: <f87c9c81-37ab-48eb-4031-dca89f8fce37@arm.com>
Date:   Wed, 19 Dec 2018 16:14:10 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Christoffer Dall <christoffer.dall@....com>,
        Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [WRONG] KVM: arm/arm64: vgic: fix off-by-one bug in
 vgic_get_irq()

Hi Gustavo,

On 19/12/2018 15:11, Gustavo A. R. Silva wrote:
> Hi Marc,
> 
> This is wrong: commit 6022fcc0e87a0eb5e9a72b15ed70dd29ebcb7343
> 
> The above is not my original patch and it should not be tagged for stable,
> as it introduces the same kind of bug I intended to fix:
> 
> array_index_nospec() can now return kvm->arch.vgic.nr_spis + VGIC_NR_PRIVATE_IRQS
> and this is not what you want. So, in this case the following line of code
> is just fine as it is:
> 
> intid = array_index_nospec(intid, kvm->arch.vgic.nr_spis + VGIC_NR_PRIVATE_IRQS); 
> 
> 
> As the commit log says, my patch fixes:
> 
> commit 41b87599c74300027f305d7b34368ec558978ff2
> 
> not both:
> 
> commit 41b87599c74300027f305d7b34368ec558978ff2
> 
> and 
> 
> commit bea2ef803ade3359026d5d357348842bca9edcf1
> 
> If you want to apply the fix on top of bea2ef803ade3359026d5d357348842bca9edcf1
> then you should apply this instead:
> 
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index bb1a83345741..e607547c7bb0 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -103,7 +103,7 @@ struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
>  {
>         /* SGIs and PPIs */
>         if (intid <= VGIC_MAX_PRIVATE) {
> -               intid = array_index_nospec(intid, VGIC_MAX_PRIVATE);
> +               intid = array_index_nospec(intid, VGIC_MAX_PRIVATE + 1);
>                 return &vcpu->arch.vgic_cpu.private_irqs[intid];
>         }
>  
> 
> The commit log should remain the same.

I indeed completely fscked up the conflict resolution, clearly not
engaging my brain. I'll fix that quickly.

Thanks for the heads up.

	M.
-- 
Jazz is not dead. It just smells funny...