Re: [PATCH] pcie_sriov: Fix PCI_SRIOV_* accesses in pcie_sriov_pf_exit()

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

On Fri, Dec 05, 2025 at 03:57:18PM +0100, Kevin Wolf wrote:
> PCI_SRIOV_* are offsets into the SR-IOV capability, not into the PCI
> config space. pcie_sriov_pf_exit() erroneously takes them as the latter,
> which makes it read PCI_HEADER_TYPE and PCI_BIST when it tries to read
> PCI_SRIOV_TOTAL_VF.
> 
> In many cases we're lucky enough that the PCI config space will be 0
> there, so we just skip the whole for loop, but this isn't guaranteed.
> For example, setting the multifunction bit on the PF and then doing a
> 'device_del' on it will get a larger number and cause a segfault.
> 
> Fix this and access the real PCI_SRIOV_* fields in the capability.
> 
> Cc: qemu-stable@nongnu.org
> Fixes: 19e55471d4e8 ('pcie_sriov: Allow user to create SR-IOV device')
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Thanks for the patch! something small to improve:

> ---
>  hw/pci/pcie_sriov.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/pci/pcie_sriov.c b/hw/pci/pcie_sriov.c
> index c4f88f09757..d467284cbda 100644
> --- a/hw/pci/pcie_sriov.c
> +++ b/hw/pci/pcie_sriov.c
> @@ -195,14 +195,17 @@ bool pcie_sriov_pf_init(PCIDevice *dev, uint16_t offset,
>  
>  void pcie_sriov_pf_exit(PCIDevice *dev)
>  {
> +    uint8_t *cfg;
> +
>      if (dev->exp.sriov_cap == 0) {
>          return;
>      }
> +    cfg = dev->config + dev->exp.sriov_cap;

initialize cfg at the point of declaration maybe? I think it would
be clearer.

>  
>      if (dev->exp.sriov_pf.vf_user_created) {
>          uint16_t ven_id = pci_get_word(dev->config + PCI_VENDOR_ID);
> -        uint16_t total_vfs = pci_get_word(dev->config + PCI_SRIOV_TOTAL_VF);
> -        uint16_t vf_dev_id = pci_get_word(dev->config + PCI_SRIOV_VF_DID);
> +        uint16_t total_vfs = pci_get_word(cfg + PCI_SRIOV_TOTAL_VF);
> +        uint16_t vf_dev_id = pci_get_word(cfg + PCI_SRIOV_VF_DID);
>  
>          unregister_vfs(dev);
>  
> @@ -213,8 +216,6 @@ 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));
>      }
>  }
> -- 
> 2.52.0