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

[Kevin Wolf <kwolf@redhat.com>]

Am 05.12.2025 um 16:03 hat Michael S. Tsirkin geschrieben:
> 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.

That's what I had first, then changed it to make it clearer that the
pointer is only guaranteed to be valid after the dev->exp.sriov_cap
check. But either way works for me. Let me know if I should send a v2
that puts it back on the top.

Kevin