Subject: [PATCH v3 09/11] KVM: arm/arm64: vgic: Prevent userspace injection of a mapped interrupt

From: [email-masked] (Christoffer Dall)
Date: Tue, 4 Aug 2015 19:38:07 +0200

On Tue, Aug 04, 2015 at 05:02:41PM +0100, Marc Zyngier wrote:
> On 04/08/15 14:45, Christoffer Dall wrote:
> > On Fri, Jul 24, 2015 at 04:55:07PM +0100, Marc Zyngier wrote:
> >> Virtual interrupts mapped to a HW interrupt should only be triggered
> >> from inside the kernel. Otherwise, you could end up confusing the
> >> kernel (and the GIC's) state machine.
> >>
> >> Rearrange the injection path so that kvm_vgic_inject_irq is
> >> used for non-mapped interrupts, and kvm_vgic_inject_mapped_irq is
> >> used for mapped interrupts. The latter should only be called from
> >> inside the kernel (timer, VFIO).
> >>
> >> Signed-off-by: Marc Zyngier <[email-masked]>
> >> ---
> >>  include/kvm/arm_vgic.h |  2 +
> >>  virt/kvm/arm/vgic.c    | 99 ++++++++++++++++++++++++++++++++++----------------
> >>  2 files changed, 70 insertions(+), 31 deletions(-)
> >>
> >> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> >> index 7306b4b..f6bfd79 100644
> >> --- a/include/kvm/arm_vgic.h
> >> +++ b/include/kvm/arm_vgic.h
> >> @@ -351,6 +351,8 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu);
> >>  void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu);
> >>  int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
> >>  			bool level);
> >> +int kvm_vgic_inject_mapped_irq(struct kvm *kvm, int cpuid,
> >> +			       struct irq_phys_map *map, bool level);
> >>  void vgic_v3_dispatch_sgi(struct kvm_vcpu *vcpu, u64 reg);
> >>  int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu);
> >>  int kvm_vgic_vcpu_active_irq(struct kvm_vcpu *vcpu);
> >> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> >> index 3f7b690..e40ef70 100644
> >> --- a/virt/kvm/arm/vgic.c
> >> +++ b/virt/kvm/arm/vgic.c
> >> @@ -1533,7 +1533,8 @@ static int vgic_validate_injection(struct kvm_vcpu *vcpu, int irq, int level)
> >>  }
> >>  
> >>  static int vgic_update_irq_pending(struct kvm *kvm, int cpuid,
> >> -				  unsigned int irq_num, bool level)
> >> +				   struct irq_phys_map *map,
> >> +				   unsigned int irq_num, bool level)
> >>  {
> >>  	struct vgic_dist *dist = &kvm->arch.vgic;
> >>  	struct kvm_vcpu *vcpu;
> >> @@ -1541,6 +1542,9 @@ static int vgic_update_irq_pending(struct kvm *kvm, int cpuid,
> >>  	int enabled;
> >>  	bool ret = true, can_inject = true;
> >>  
> >> +	if (irq_num >= min(kvm->arch.vgic.nr_irqs, 1020))
> >> +		return -EINVAL;
> >> +
> >>  	spin_lock(&dist->lock);
> >>  
> >>  	vcpu = kvm_get_vcpu(kvm, cpuid);
> >> @@ -1603,14 +1607,42 @@ static int vgic_update_irq_pending(struct kvm *kvm, int cpuid,
> >>  out:
> >>  	spin_unlock(&dist->lock);
> >>  
> >> -	return ret ? cpuid : -EINVAL;
> >> +	if (!ret) {
> > 
> > don't you mean if (ret) here?  hint: ret is a bool
> 
> Ouch. Nice catch!
> 
> > 
> >> +		/* kick the specified vcpu */
> >> +		kvm_vcpu_kick(kvm_get_vcpu(kvm, cpuid));
> >> +	}
> >> +
> >> +	return 0;
> > 
> > isn't this a change in the internal API?
> > Before, we would return -EINVAL when ret is false.  Not sure if this
> > has any consequences though?
> 
> I don't think this is a change in API. Before this patch, we would
> either return a vcpuid or -EINVAL. But the error would not be propagated
> beyond kvm_vgic_inject_irq, effectively discarding the error code.
> 
> Also, it is a bit odd to return an error because the toggling of the
> line wasn't significant (like bringing the line down on an
> edge-triggered interrupt).
> 

true, indeed, my brain was too fried to think it through.

(why does coming back from vacation always involve paging in weird vgic
stuff for me?)

> > 
> >> +}
> >> +
> >> +static int vgic_lazy_init(struct kvm *kvm)
> >> +{
> >> +	int ret = 0;
> >> +
> >> +	if (unlikely(!vgic_initialized(kvm))) {
> >> +		/*
> >> +		 * We only provide the automatic initialization of the VGIC
> >> +		 * for the legacy case of a GICv2. Any other type must
> >> +		 * be explicitly initialized once setup with the respective
> >> +		 * KVM device call.
> >> +		 */
> >> +		if (kvm->arch.vgic.vgic_model != KVM_DEV_TYPE_ARM_VGIC_V2)
> >> +			return -EBUSY;
> >> +
> >> +		mutex_lock(&kvm->lock);
> >> +		ret = vgic_init(kvm);
> >> +		mutex_unlock(&kvm->lock);
> >> +	}
> >> +
> >> +	return ret;
> >>  }
> >>  
> >>  /**
> >>   * kvm_vgic_inject_irq - Inject an IRQ from a device to the vgic
> >>   * @kvm:     The VM structure pointer
> >>   * @cpuid:   The CPU for PPIs
> >> - * @irq_num: The IRQ number that is assigned to the device
> >> + * @irq_num: The IRQ number that is assigned to the device. This IRQ
> >> + *           must not be mapped to a HW interrupt.
> >>   * @level:   Edge-triggered:  true:  to trigger the interrupt
> >>   *			      false: to ignore the call
> >>   *	     Level-sensitive  true:  activates an interrupt
> >> @@ -1623,39 +1655,44 @@ out:
> >>  int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
> >>  			bool level)
> >>  {
> >> -	int ret = 0;
> >> -	int vcpu_id;
> >> -
> >> -	if (unlikely(!vgic_initialized(kvm))) {
> >> -		/*
> >> -		 * We only provide the automatic initialization of the VGIC
> >> -		 * for the legacy case of a GICv2. Any other type must
> >> -		 * be explicitly initialized once setup with the respective
> >> -		 * KVM device call.
> >> -		 */
> >> -		if (kvm->arch.vgic.vgic_model != KVM_DEV_TYPE_ARM_VGIC_V2) {
> >> -			ret = -EBUSY;
> >> -			goto out;
> >> -		}
> >> -		mutex_lock(&kvm->lock);
> >> -		ret = vgic_init(kvm);
> >> -		mutex_unlock(&kvm->lock);
> >> +	struct irq_phys_map *map;
> >> +	int ret;
> >>  
> >> -		if (ret)
> >> -			goto out;
> >> -	}
> >> +	ret = vgic_lazy_init(kvm);
> >> +	if (ret)
> >> +		return ret;
> >>  
> >> -	if (irq_num >= min(kvm->arch.vgic.nr_irqs, 1020))
> >> +	map = vgic_irq_map_search(kvm_get_vcpu(kvm, cpuid), irq_num);
> >> +	if (map)
> >>  		return -EINVAL;
> >>  
> >> -	vcpu_id = vgic_update_irq_pending(kvm, cpuid, irq_num, level);
> >> -	if (vcpu_id >= 0) {
> >> -		/* kick the specified vcpu */
> >> -		kvm_vcpu_kick(kvm_get_vcpu(kvm, vcpu_id));
> >> -	}
> >> +	return vgic_update_irq_pending(kvm, cpuid, NULL, irq_num, level);
> >> +}
> >>  
> >> -out:
> >> -	return ret;
> >> +/**
> >> + * kvm_vgic_inject_mapped_irq - Inject a physically mapped IRQ to the vgic
> >> + * @kvm:     The VM structure pointer
> >> + * @cpuid:   The CPU for PPIs
> >> + * @map:     Pointer to a irq_phys_map structure describing the mapping
> >> + * @level:   Edge-triggered:  true:  to trigger the interrupt
> >> + *			      false: to ignore the call
> >> + *	     Level-sensitive  true:  activates an interrupt
> >> + *			      false: deactivates an interrupt
> > 
> > just noticed this unfortunate use of the words 'activate/deactivate'
> > here, which is not true, it just raises/lowers the input signal...
> > 
> 
> I'll clean that up.
> 

Thanks,
-Christoffer