linux-kernel - Re: [PATCH v5 03/10] KVM: arm/arm64: vgic-its: Check CBASER/BASER validity before enabling the ITS

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Date:   Wed, 25 Oct 2017 10:38:13 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     <eric.auger.pro@...il.com>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <cdall@...aro.org>, <peter.maydell@...aro.org>,
        <andre.przywara@....com>, <wanghaibin.wang@...wei.com>,
        <wu.wubin@...wei.com>, <drjones@...hat.com>, <wei@...hat.com>
Subject: Re: [PATCH v5 03/10] KVM: arm/arm64: vgic-its: Check CBASER/BASER validity before enabling the ITS

On Mon, Oct 23 2017 at  4:08:22 pm BST, Eric Auger <eric.auger@...hat.com> wrote:
> The spec says it is UNPREDICTABLE to enable the ITS
> if any of the following conditions are true:
>
> - GITS_CBASER.Valid == 0.
> - GITS_BASER<n>.Valid == 0, for any GITS_BASER<n> register
>   where the Type field indicates Device.
> - GITS_BASER<n>.Valid == 0, for any GITS_BASER<n> register
>   where the Type field indicates Interrupt Collection and
>   GITS_TYPER.HCC == 0.
>
> In that case, let's keep the ITS disabled.
>
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> Reported-by: Andre Przywara <andre.przywara@....com>
>
> ---
>
> need to be CC'ed stable
>
> v4 -> v5:
> - check the condition before updating its->enabled and
>   fix its->cbaser && GITS_CBASER_VALID
>
> v3: creation
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index b0ba80f..1eb355e 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -1466,6 +1466,16 @@ static void vgic_mmio_write_its_ctlr(struct kvm *kvm, struct vgic_its *its,
>  {
>  	mutex_lock(&its->cmd_lock);
>  
> +	/*
> +	 * It is UNPREDICTABLE to enable the ITS if any of the CBASER or
> +	 * device/collection BASER are invalid
> +	 */
> +	if (!its->enabled && (val & GITS_CTLR_ENABLE) &&
> +		(!(its->baser_device_table & GITS_BASER_VALID) ||
> +		 !(its->baser_coll_table & GITS_BASER_VALID) ||
> +		 !(its->cbaser & GITS_CBASER_VALID)))
> +		goto out;
> +
>  	its->enabled = !!(val & GITS_CTLR_ENABLE);
>  
>  	/*
> @@ -1474,6 +1484,7 @@ static void vgic_mmio_write_its_ctlr(struct kvm *kvm, struct vgic_its *its,
>  	 */
>  	vgic_its_process_commands(kvm, its);
>  
> +out:
>  	mutex_unlock(&its->cmd_lock);
>  }

While this is definitely a good hardening of the implementation, I don't
think it fixes anything for the guest which is already misbehaving and
would just not get anything out of this misconfigurarion (in line with
the UNPRED requirement).

So I don't think we need to Cc stable for this. Otherwise:

Reviewed-by: Marc Zyngier <marc.zyngier@....com>

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