Re: [PULL 04/46] virtio-pci: Fix the use of an uninitialized irqfd.

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 04, 2024 at 03:06:15PM -0400, Michael S. Tsirkin wrote:
> From: Cindy Lu <lulu@redhat.com>
> 
> The crash was reported in MAC OS and NixOS, here is the link for this bug
> https://gitlab.com/qemu-project/qemu/-/issues/2334
> https://gitlab.com/qemu-project/qemu/-/issues/2321
> 
> The root cause is that the function virtio_pci_set_guest_notifiers() only
> initializes the irqfd when the use_guest_notifier_mask and guest_notifier_mask
> are set.
> However, this check is missing in virtio_pci_set_vector().
> So the fix is to add this check.
> 
> This fix is verified in vyatta,MacOS,NixOS,fedora system.
> 
> The bt tree for this bug is:
> Thread 6 "CPU 0/KVM" received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7c817be006c0 (LWP 1269146)]
> kvm_virtio_pci_vq_vector_use () at ../qemu-9.0.0/hw/virtio/virtio-pci.c:817
> 817	    if (irqfd->users == 0) {
> (gdb) thread apply all bt
> ...
> Thread 6 (Thread 0x7c817be006c0 (LWP 1269146) "CPU 0/KVM"):
> 0  kvm_virtio_pci_vq_vector_use () at ../qemu-9.0.0/hw/virtio/virtio-pci.c:817
> 1  kvm_virtio_pci_vector_use_one () at ../qemu-9.0.0/hw/virtio/virtio-pci.c:893
> 2  0x00005983657045e2 in memory_region_write_accessor () at ../qemu-9.0.0/system/memory.c:497
> 3  0x0000598365704ba6 in access_with_adjusted_size () at ../qemu-9.0.0/system/memory.c:573
> 4  0x0000598365705059 in memory_region_dispatch_write () at ../qemu-9.0.0/system/memory.c:1528
> 5  0x00005983659b8e1f in flatview_write_continue_step.isra.0 () at ../qemu-9.0.0/system/physmem.c:2713
> 6  0x000059836570ba7d in flatview_write_continue () at ../qemu-9.0.0/system/physmem.c:2743
> 7  flatview_write () at ../qemu-9.0.0/system/physmem.c:2774
> 8  0x000059836570bb76 in address_space_write () at ../qemu-9.0.0/system/physmem.c:2894
> 9  0x0000598365763afe in address_space_rw () at ../qemu-9.0.0/system/physmem.c:2904
> 10 kvm_cpu_exec () at ../qemu-9.0.0/accel/kvm/kvm-all.c:2917
> 11 0x000059836576656e in kvm_vcpu_thread_fn () at ../qemu-9.0.0/accel/kvm/kvm-accel-ops.c:50
> 12 0x0000598365926ca8 in qemu_thread_start () at ../qemu-9.0.0/util/qemu-thread-posix.c:541
> 13 0x00007c8185bcd1cf in ??? () at /usr/lib/libc.so.6
> 14 0x00007c8185c4e504 in clone () at /usr/lib/libc.so.6
> 
> Fixes: 2ce6cff94d ("virtio-pci: fix use of a released vector")
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Cindy Lu <lulu@redhat.com>
> Message-Id: <20240522051042.985825-1-lulu@redhat.com>
> Acked-by: Jason Wang <jasowang@redhat.com>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>


Dropped now at author's request.

> ---
>  hw/virtio/virtio-pci.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index b1d02f4b3d..a7faee5b33 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1431,6 +1431,7 @@ static void virtio_pci_set_vector(VirtIODevice *vdev,
>  {
>      bool kvm_irqfd = (vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
>          msix_enabled(&proxy->pci_dev) && kvm_msi_via_irqfd_enabled();
> +    VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
>  
>      if (new_vector == old_vector) {
>          return;
> @@ -1441,7 +1442,8 @@ static void virtio_pci_set_vector(VirtIODevice *vdev,
>       * set, we need to release the old vector and set up the new one.
>       * Otherwise just need to set the new vector on the device.
>       */
> -    if (kvm_irqfd && old_vector != VIRTIO_NO_VECTOR) {
> +    if (kvm_irqfd && old_vector != VIRTIO_NO_VECTOR &&
> +        vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
>          kvm_virtio_pci_vector_release_one(proxy, queue_no);
>      }
>      /* Set the new vector on the device. */
> @@ -1451,7 +1453,8 @@ static void virtio_pci_set_vector(VirtIODevice *vdev,
>          virtio_queue_set_vector(vdev, queue_no, new_vector);
>      }
>      /* If the new vector changed need to set it up. */
> -    if (kvm_irqfd && new_vector != VIRTIO_NO_VECTOR) {
> +    if (kvm_irqfd && new_vector != VIRTIO_NO_VECTOR &&
> +        vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
>          kvm_virtio_pci_vector_use_one(proxy, queue_no);
>      }
>  }
> -- 
> MST
>