linux-kernel - Re: [Patch v2] KVM: x86: Initializing all kvm_lapic_irq fields in ioapic_write

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Date:   Fri, 13 Mar 2020 14:25:51 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Nitesh Narayan Lal <nitesh@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        mtosatti@...hat.com, sean.j.christopherson@...el.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        pbonzini@...hat.com, peterx@...hat.com
Subject: Re: [Patch v2] KVM: x86: Initializing all kvm_lapic_irq fields in ioapic_write_indirect

Nitesh Narayan Lal <nitesh@...hat.com> writes:

> Previously all fields of structure kvm_lapic_irq were not initialized
> before it was passed to kvm_bitmap_or_dest_vcpus(). Which will cause
> an issue when any of those fields are used for processing a request.
> For example not initializing the msi_redir_hint field before passing
> to the kvm_bitmap_or_dest_vcpus(), may lead to a misbehavior of
> kvm_apic_map_get_dest_lapic(). This will specifically happen when the
> kvm_lowest_prio_delivery() returns TRUE due to a non-zero garbage
> value of msi_redir_hint, which should not happen as the request belongs
> to APIC fixed delivery mode and we do not want to deliver the
> interrupt only to the lowest priority candidate.
>
> This patch initializes all the fields of kvm_lapic_irq based on the
> values of ioapic redirect_entry object before passing it on to
> kvm_bitmap_or_dest_vcpus().
>
> Fixes: 7ee30bc132c6("KVM: x86: deliver KVM IOAPIC scan request to target vCPUs")
> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
> ---
>  arch/x86/kvm/ioapic.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
> index 7668fed..3a8467d 100644
> --- a/arch/x86/kvm/ioapic.c
> +++ b/arch/x86/kvm/ioapic.c
> @@ -378,12 +378,15 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
>  		if (e->fields.delivery_mode == APIC_DM_FIXED) {
>  			struct kvm_lapic_irq irq;
>  
> -			irq.shorthand = APIC_DEST_NOSHORT;
>  			irq.vector = e->fields.vector;
>  			irq.delivery_mode = e->fields.delivery_mode << 8;
> -			irq.dest_id = e->fields.dest_id;
>  			irq.dest_mode =
>  			    kvm_lapic_irq_dest_mode(!!e->fields.dest_mode);
> +			irq.level = 1;

'level' is bool in struct kvm_lapic_irq but other than that, is there a
reason we set it to 'true' here? I understand that any particular
setting is likely better than random and it should actually not be used
without setting it first but still?

> +			irq.trig_mode = e->fields.trig_mode;
> +			irq.shorthand = APIC_DEST_NOSHORT;
> +			irq.dest_id = e->fields.dest_id;
> +			irq.msi_redir_hint = false;
>  			bitmap_zero(&vcpu_bitmap, 16);
>  			kvm_bitmap_or_dest_vcpus(ioapic->kvm, &irq,
>  						 &vcpu_bitmap);

-- 
Vitaly