Re: [PATCH] PCI/IOV: Fix out-of-bounds access in sriov_restore_vf_rebar_state()

[Bjorn Helgaas]

On Wed, Apr 08, 2026 at 06:39:22PM +0200, Marco Nenciarini wrote:
> sriov_restore_vf_rebar_state() extracts bar_idx from the VF Resizable
> BAR control register using a 3-bit field (PCI_VF_REBAR_CTRL_BAR_IDX,
> bits 0-2), which yields values in the range 0-7. This value is then
> used to index into dev->sriov->barsz[], which has PCI_SRIOV_NUM_BARS
> (6) entries.
> 
> If the PCI config space read returns garbage data (e.g. 0xffffffff when
> the device is no longer accessible on the bus), bar_idx is 7, causing
> an out-of-bounds array access. UBSAN reports this as:
> 
>   UBSAN: array-index-out-of-bounds in drivers/pci/iov.c:948:51
>   index 7 is out of range for type 'resource_size_t [6]'
> 
> This was observed on an NVIDIA RTX PRO 1000 GPU (GB207GLM) that fell
> off the PCIe bus during a failed GC6 power state exit. The subsequent
> pci_restore_state() call triggered the UBSAN splat in
> sriov_restore_vf_rebar_state() since all config space reads returned
> 0xffffffff.
> 
> Add a bounds check on bar_idx before using it as an array index to
> prevent the out-of-bounds access.

I think pci_restore_rebar_state() has a similar problem: if the device
doesn't respond, "nbars" will be 7 (legal values are 1-6), and
"bar_idx" will also be 7 (legal values 0-5).  We use "bar_idx" for
pci_resource_n(), and dev->resource[7] does exist but is not a valid
BAR.

> Fixes: 5a8f77e24a30 ("PCI/IOV: Restore VF resizable BAR state after reset")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Marco Nenciarini <mnencia@xxxxxxxx>
> ---
> Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> Cc: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
> 
>  drivers/pci/iov.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 00784a60b..521f2cb64 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -946,6 +946,8 @@ static void sriov_restore_vf_rebar_state(struct pci_dev *dev)
>  
>  		pci_read_config_dword(dev, pos + PCI_VF_REBAR_CTRL, &ctrl);
>  		bar_idx = FIELD_GET(PCI_VF_REBAR_CTRL_BAR_IDX, ctrl);
> +		if (bar_idx >= PCI_SRIOV_NUM_BARS)
> +			continue;

Both here and in pci_restore_rebar_state(), we blindly use "nbars"
derived from a value that might be ~0 because the config read failed.
If we fix these, I think we should do something like this so it's
obvious why we're checking:

  pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
  if (PCI_POSSIBLE_ERROR(ctrl))
    return;

  nbars = FIELD_GET(PCI_REBAR_CTRL_NBAR_MASK, ctrl);
  for (i = 0; i < nbars; ...) {
    ...
    pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
    if (PCI_POSSIBLE_ERROR(ctrl))
      return;

    bar_idx = ctrl & PCI_REBAR_CTRL_BAR_IDX;
    res = pci_resource_n(pdev, bar_idx);

It's true that "nbars" and "bar_idx" *could* still be invalid even if
the config read succeeded, but that would be a device defect.

>  		size = pci_rebar_bytes_to_size(dev->sriov->barsz[bar_idx]);
>  		ctrl &= ~PCI_VF_REBAR_CTRL_BAR_SIZE;
>  		ctrl |= FIELD_PREP(PCI_VF_REBAR_CTRL_BAR_SIZE, size);
> -- 
> 2.47.3
>