Re: [PATCH v2] vfio/pci: Verify each MSI vector to avoid invalid MSI vectors

[Marc Zyngier]

On Wed, 23 Nov 2022 01:42:36 +0000,
chenxiang <chenxiang66@hisilicon.com> wrote:
> 
> From: Xiang Chen <chenxiang66@hisilicon.com>
> 
> Currently the number of MSI vectors comes from register PCI_MSI_FLAGS
> which should be power-of-2 in qemu, in some scenaries it is not the same as
> the number that driver requires in guest, for example, a PCI driver wants
> to allocate 6 MSI vecotrs in guest, but as the limitation, it will allocate
> 8 MSI vectors. So it requires 8 MSI vectors in qemu while the driver in
> guest only wants to allocate 6 MSI vectors.
> 
> When GICv4.1 is enabled, it iterates over all possible MSIs and enable the
> forwarding while the guest has only created some of mappings in the virtual
> ITS, so some calls fail. The exception print is as following:
> vfio-pci 0000:3a:00.1: irq bypass producer (token 000000008f08224d) 
> registration
> fails:66311
> 
> To avoid the issue, verify each MSI vector, skip some operations such as
> request_irq() and irq_bypass_register_producer() for those invalid MSI 
> vectors.
> 
> Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
> ---
> I reported the issue at the link:
> https://lkml.kernel.org/lkml/87cze9lcut.wl-maz@kernel.org/T/
> 
> Change Log:
> v1 -> v2:
> Verify each MSI vector in kernel instead of adding systemcall according to
> Mar's suggestion
> ---
>  arch/arm64/kvm/vgic/vgic-irqfd.c  | 13 +++++++++++++
>  arch/arm64/kvm/vgic/vgic-its.c    | 36 ++++++++++++++++++++++++++++++++++++
>  arch/arm64/kvm/vgic/vgic.h        |  1 +
>  drivers/vfio/pci/vfio_pci_intrs.c | 33 +++++++++++++++++++++++++++++++++
>  include/linux/kvm_host.h          |  2 ++
>  5 files changed, 85 insertions(+)
> 
> diff --git a/arch/arm64/kvm/vgic/vgic-irqfd.c 
> b/arch/arm64/kvm/vgic/vgic-irqfd.c
> index 475059b..71f6af57 100644
> --- a/arch/arm64/kvm/vgic/vgic-irqfd.c
> +++ b/arch/arm64/kvm/vgic/vgic-irqfd.c
> @@ -98,6 +98,19 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
>       return vgic_its_inject_msi(kvm, &msi);
>  }
>  
> +int kvm_verify_msi(struct kvm *kvm,
> +                struct kvm_kernel_irq_routing_entry *irq_entry)
> +{
> +     struct kvm_msi msi;
> +
> +     if (!vgic_has_its(kvm))
> +             return -ENODEV;
> +
> +     kvm_populate_msi(irq_entry, &msi);
> +
> +     return vgic_its_verify_msi(kvm, &msi);
> +}
> +
>  /**
>   * kvm_arch_set_irq_inatomic: fast-path for irqfd injection
>   */
> diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
> index 94a666d..8312a4a 100644
> --- a/arch/arm64/kvm/vgic/vgic-its.c
> +++ b/arch/arm64/kvm/vgic/vgic-its.c
> @@ -767,6 +767,42 @@ int vgic_its_inject_cached_translation(struct kvm *kvm, 
> struct kvm_msi *msi)
>       return 0;
>  }
>  
> +int vgic_its_verify_msi(struct kvm *kvm, struct kvm_msi *msi)
> +{
> +     struct vgic_its *its;
> +     struct its_ite *ite;
> +     struct kvm_vcpu *vcpu;
> +     int ret = 0;
> +
> +     if (!irqchip_in_kernel(kvm) || (msi->flags & ~KVM_MSI_VALID_DEVID))
> +             return -EINVAL;
> +
> +     if (!vgic_has_its(kvm))
> +             return -ENODEV;
> +
> +     its = vgic_msi_to_its(kvm, msi);
> +     if (IS_ERR(its))
> +             return PTR_ERR(its);
> +
> +     mutex_lock(&its->its_lock);
> +     if (!its->enabled) {
> +             ret = -EBUSY;
> +             goto unlock;
> +     }
> +     ite = find_ite(its, msi->devid, msi->data);
> +     if (!ite || !its_is_collection_mapped(ite->collection)) {
> +             ret = E_ITS_INT_UNMAPPED_INTERRUPT;
> +             goto unlock;
> +     }
> +
> +     vcpu = kvm_get_vcpu(kvm, ite->collection->target_addr);
> +     if (!vcpu)
> +             ret = E_ITS_INT_UNMAPPED_INTERRUPT;

I'm sorry, but what does this mean to the caller? This should never
leak outside of the ITS code.

> +unlock:
> +     mutex_unlock(&its->its_lock);
> +     return ret;
> +}
> +
>  /*
>   * Queries the KVM IO bus framework to get the ITS pointer from the given
>   * doorbell address.
> diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
> index 0c8da72..d452150 100644
> --- a/arch/arm64/kvm/vgic/vgic.h
> +++ b/arch/arm64/kvm/vgic/vgic.h
> @@ -240,6 +240,7 @@ int kvm_vgic_register_its_device(void);
>  void vgic_enable_lpis(struct kvm_vcpu *vcpu);
>  void vgic_flush_pending_lpis(struct kvm_vcpu *vcpu);
>  int vgic_its_inject_msi(struct kvm *kvm, struct kvm_msi *msi);
> +int vgic_its_verify_msi(struct kvm *kvm, struct kvm_msi *msi);
>  int vgic_v3_has_attr_regs(struct kvm_device *dev, struct kvm_device_attr 
> *attr);
>  int vgic_v3_dist_uaccess(struct kvm_vcpu *vcpu, bool is_write,
>                        int offset, u32 *val);
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c 
> b/drivers/vfio/pci/vfio_pci_intrs.c
> index 40c3d7c..3027805 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -19,6 +19,7 @@
>  #include <linux/vfio.h>
>  #include <linux/wait.h>
>  #include <linux/slab.h>
> +#include <linux/kvm_irqfd.h>
>  
>  #include "vfio_pci_priv.h"
>  
> @@ -315,6 +316,28 @@ static int vfio_msi_enable(struct vfio_pci_core_device 
> *vdev, int nvec, bool msi
>       return 0;
>  }
>  
> +static int vfio_pci_verify_msi_entry(struct vfio_pci_core_device *vdev,
> +             struct eventfd_ctx *trigger)
> +{
> +     struct kvm *kvm = vdev->vdev.kvm;
> +     struct kvm_kernel_irqfd *tmp;
> +     struct kvm_kernel_irq_routing_entry irq_entry;
> +     int ret = -ENODEV;
> +
> +     spin_lock_irq(&kvm->irqfds.lock);
> +     list_for_each_entry(tmp, &kvm->irqfds.items, list) {
> +             if (trigger == tmp->eventfd) {
> +                     ret = 0;
> +                     break;
> +             }
> +     }
> +     spin_unlock_irq(&kvm->irqfds.lock);
> +     if (ret)
> +             return ret;
> +     irq_entry = tmp->irq_entry;
> +     return kvm_verify_msi(kvm, &irq_entry);

How does this work on !arm64? Why do we need an on-stack version of
tmp->irq_entry?

> +}
> +
>  static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
>                                     int vector, int fd, bool msix)
>  {
> @@ -355,6 +378,16 @@ static int vfio_msi_set_vector_signal(struct 
> vfio_pci_core_device *vdev,
>               return PTR_ERR(trigger);
>       }
>  
> +     if (!msix) {
> +             ret = vfio_pci_verify_msi_entry(vdev, trigger);
> +             if (ret) {
> +                     kfree(vdev->ctx[vector].name);
> +                     eventfd_ctx_put(trigger);
> +                     if (ret > 0)
> +                             ret = 0;
> +                     return ret;
> +             }
> +     }

Honestly, the whole things seems really complicated to avoid something
that is only a harmless warning . How about just toning down the
message instead?

        M.

-- 
Without deviation from the norm, progress is not possible.