Re: [PATCH v6] virtio-pci: Fix the crash that the vector was used after released.

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

On Fri, Apr 12, 2024 at 02:26:55PM +0800, Cindy Lu wrote:
> During the booting process of the non-standard image, the behavior of the
> called function in qemu is as follows:
> 
> 1. vhost_net_stop() was triggered by guest image. This will call the function
> virtio_pci_set_guest_notifiers() with assgin= false,
> virtio_pci_set_guest_notifiers(） will release the irqfd for vector 0
> 
> 2. virtio_reset() was triggered, this will set configure vector to VIRTIO_NO_VECTOR
> 
> 3.vhost_net_start() was called (at this time, the configure vector is
> still VIRTIO_NO_VECTOR) and then call virtio_pci_set_guest_notifiers() with
> assgin=true, so the irqfd for vector 0 is still not "init" during this process
> 
> 4. The system continues to boot and sets the vector back to 0. After that
> msix_fire_vector_notifier() was triggered to unmask the vector 0 and  meet the crash
> 
> To fix the issue, we need to support changing the vector after VIRTIO_CONFIG_S_DRIVER_OK is set.
> 
> (gdb) bt
> 0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0)
>     at pthread_kill.c:44
> 1  0x00007fc87148ec53 in __pthread_kill_internal (signo=6, threadid=<optimized out>) at pthread_kill.c:78
> 2  0x00007fc87143e956 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
> 3  0x00007fc8714287f4 in __GI_abort () at abort.c:79
> 4  0x00007fc87142871b in __assert_fail_base
>     (fmt=0x7fc8715bbde0 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=0x5606413efd53 "ret == 0", file=0x5606413ef87d "../accel/kvm/kvm-all.c", line=1837, function=<optimized out>) at assert.c:92
> 5  0x00007fc871437536 in __GI___assert_fail
>     (assertion=0x5606413efd53 "ret == 0", file=0x5606413ef87d "../accel/kvm/kvm-all.c", line=1837, function=0x5606413f06f0 <__PRETTY_FUNCTION__.19> "kvm_irqchip_commit_routes") at assert.c:101
> 6  0x0000560640f884b5 in kvm_irqchip_commit_routes (s=0x560642cae1f0) at ../accel/kvm/kvm-all.c:1837
> 7  0x0000560640c98f8e in virtio_pci_one_vector_unmask
>     (proxy=0x560643c65f00, queue_no=4294967295, vector=0, msg=..., n=0x560643c6e4c8)
>     at ../hw/virtio/virtio-pci.c:1005
> 8  0x0000560640c99201 in virtio_pci_vector_unmask (dev=0x560643c65f00, vector=0, msg=...)
>     at ../hw/virtio/virtio-pci.c:1070
> 9  0x0000560640bc402e in msix_fire_vector_notifier (dev=0x560643c65f00, vector=0, is_masked=false)
>     at ../hw/pci/msix.c:120
> 10 0x0000560640bc40f1 in msix_handle_mask_update (dev=0x560643c65f00, vector=0, was_masked=true)
>     at ../hw/pci/msix.c:140
> 11 0x0000560640bc4503 in msix_table_mmio_write (opaque=0x560643c65f00, addr=12, val=0, size=4)
>     at ../hw/pci/msix.c:231
> 12 0x0000560640f26d83 in memory_region_write_accessor
>     (mr=0x560643c66540, addr=12, value=0x7fc86b7bc628, size=4, shift=0, mask=4294967295, attrs=...)
>     at ../system/memory.c:497
> 13 0x0000560640f270a6 in access_with_adjusted_size
> 
>      (addr=12, value=0x7fc86b7bc628, size=4, access_size_min=1, access_size_max=4, access_fn=0x560640f26c8d <memory_region_write_accessor>, mr=0x560643c66540, attrs=...) at ../system/memory.c:573
> 14 0x0000560640f2a2b5 in memory_region_dispatch_write (mr=0x560643c66540, addr=12, data=0, op=MO_32, attrs=...)
>     at ../system/memory.c:1521
> 15 0x0000560640f37bac in flatview_write_continue
>     (fv=0x7fc65805e0b0, addr=4273803276, attrs=..., ptr=0x7fc871e9c028, len=4, addr1=12, l=4, mr=0x560643c66540)
>     at ../system/physmem.c:2714
> 16 0x0000560640f37d0f in flatview_write
>     (fv=0x7fc65805e0b0, addr=4273803276, attrs=..., buf=0x7fc871e9c028, len=4) at ../system/physmem.c:2756
> 17 0x0000560640f380bf in address_space_write
>     (as=0x560642161ae0 <address_space_memory>, addr=4273803276, attrs=..., buf=0x7fc871e9c028, len=4)
>     at ../system/physmem.c:2863
> 18 0x0000560640f3812c in address_space_rw
>     (as=0x560642161ae0 <address_space_memory>, addr=4273803276, attrs=..., buf=0x7fc871e9c028, len=4, is_write=true) at ../system/physmem.c:2873
> --Type <RET> for more, q to quit, c to continue without paging--
> 19 0x0000560640f8aa55 in kvm_cpu_exec (cpu=0x560642f205e0) at ../accel/kvm/kvm-all.c:2915
> 20 0x0000560640f8d731 in kvm_vcpu_thread_fn (arg=0x560642f205e0) at ../accel/kvm/kvm-accel-ops.c:51
> 21 0x00005606411949f4 in qemu_thread_start (args=0x560642f292b0) at ../util/qemu-thread-posix.c:541
> 22 0x00007fc87148cdcd in start_thread (arg=<optimized out>) at pthread_create.c:442
> 23 0x00007fc871512630 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
> (gdb)
> 
> Fixes: f9a09ca3ea ("vhost: add support for configure interrupt")
> Cc: qemu-stable@nongnu.org
>

empty line not needed here
 
> Signed-off-by: Cindy Lu <lulu@redhat.com>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

It's guest triggerable so either we merge this before the release,
or rely on stable process :(

> ---
>  hw/virtio/virtio-pci.c | 43 ++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 1a7039fb0c..f83ec92990 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1423,6 +1423,36 @@ static int virtio_pci_add_mem_cap(VirtIOPCIProxy *proxy,
>  
>      return offset;
>  }
> +static void virtio_pci_set_and_change_vector(VirtIODevice *vdev,
> +                                             VirtIOPCIProxy *proxy,
> +                                             int queue_no, uint16_t old_vector,
> +                                             uint16_t new_vector)
> +{
> +    /*
> +     * If the device uses irqfd and the vector changes after DRIVER_OK is
> +     * set, we need to release the old vector and set up the new one.
> +     * others just need to set the new vector to device
> +     */
> +    if ((vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
> +        (msix_enabled(&proxy->pci_dev) && kvm_msi_via_irqfd_enabled())) {
> +        if (old_vector != VIRTIO_NO_VECTOR) {
> +            kvm_virtio_pci_vector_release_one(proxy, queue_no);
> +        }
> +    }
> +    /*set the new vector to device*/
> +    if (queue_no == VIRTIO_CONFIG_IRQ_IDX) {
> +        vdev->config_vector = new_vector;
> +    } else {
> +        virtio_queue_set_vector(vdev, queue_no, new_vector);
> +    }
> +    /* if the new vector chanegd need to set it up */

typo

> +    if ((vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
> +        (msix_enabled(&proxy->pci_dev) && kvm_msi_via_irqfd_enabled())) {
> +        if (new_vector != VIRTIO_NO_VECTOR) {
> +            kvm_virtio_pci_vector_use_one(proxy, queue_no);
> +        }
> +    }
> +}
>  
>  int virtio_pci_add_shm_cap(VirtIOPCIProxy *proxy,
>                             uint8_t bar, uint64_t offset, uint64_t length,
> @@ -1570,7 +1600,12 @@ static void virtio_pci_common_write(void *opaque, hwaddr addr,
>          } else {
>              val = VIRTIO_NO_VECTOR;
>          }
> -        vdev->config_vector = val;
> +        vector = vdev->config_vector;
> +        /*check if need to change the vector*/
> +        if (val != vector) {
> +            virtio_pci_set_and_change_vector(vdev, proxy, VIRTIO_CONFIG_IRQ_IDX,
> +                                             vector, val);
> +        }
>          break;
>      case VIRTIO_PCI_COMMON_STATUS:
>          if (!(val & VIRTIO_CONFIG_S_DRIVER_OK)) {
> @@ -1610,7 +1645,11 @@ static void virtio_pci_common_write(void *opaque, hwaddr addr,
>          } else {
>              val = VIRTIO_NO_VECTOR;
>          }
> -        virtio_queue_set_vector(vdev, vdev->queue_sel, val);
> +        /*check if need to change the vector*/
> +        if (val != vector) {
> +            virtio_pci_set_and_change_vector(vdev, proxy, vdev->queue_sel,
> +                                             vector, val);
> +        }
>          break;
>      case VIRTIO_PCI_COMMON_Q_ENABLE:
>          if (val == 1) {
> -- 
> 2.43.0