pcie_sriov: make pcie_sriov_pf_exit() safe on non-SR-IOV devices

Commit 3f9cfaa92c96 ("virtio-pci: Implement SR-IOV PF") added an
unconditional call from virtio_pci_exit() to pcie_sriov_pf_exit().

pcie_sriov_pf_exit() reads from the SR-IOV Capability in Configuration
Space:

  uint8_t *cfg = dev->config + dev->exp.sriov_cap;
  ...
  unparent_vfs(dev, pci_get_word(cfg + PCI_SRIOV_TOTAL_VF));
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This results in undefined behavior when dev->exp.sriov_cap is 0 because
this is not an SR-IOV device. For example, unparent_vfs() segfaults when
total_vfs happens to be non-zero.

Fix this by returning early from pcie_sriov_pf_exit() when
dev->exp.sriov_cap is 0 because this is not an SR-IOV device.

Cc: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Cc: Michael S. Tsirkin <mst@redhat.com>
Reported-by: Qing Wang <qinwang@redhat.com>
Buglink: https://issues.redhat.com/browse/RHEL-116443
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Fixes: cab1398a60eb ("pcie_sriov: Reuse SR-IOV VF device instances")
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250924155153.579495-1-stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/hw/pci/pcie_sriov.c b/hw/pci/pcie_sriov.c
index 29474d749a..c4f88f0975 100644
--- a/hw/pci/pcie_sriov.c
+++ b/hw/pci/pcie_sriov.c
@@ -195,7 +195,9 @@ bool pcie_sriov_pf_init(PCIDevice *dev, uint16_t offset,
 
 void pcie_sriov_pf_exit(PCIDevice *dev)
 {
-    uint8_t *cfg = dev->config + dev->exp.sriov_cap;
+    if (dev->exp.sriov_cap == 0) {
+        return;
+    }
 
     if (dev->exp.sriov_pf.vf_user_created) {
         uint16_t ven_id = pci_get_word(dev->config + PCI_VENDOR_ID);
@@ -211,6 +213,8 @@ void pcie_sriov_pf_exit(PCIDevice *dev)
             pci_config_set_device_id(dev->exp.sriov_pf.vf[i]->config, vf_dev_id);
         }
     } else {
+        uint8_t *cfg = dev->config + dev->exp.sriov_cap;
+
         unparent_vfs(dev, pci_get_word(cfg + PCI_SRIOV_TOTAL_VF));
     }
 }