Re: [bug report] PCI: Check BAR index for validity

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Mar 10, 2025 at 08:54:54AM +0100, Philipp Stanner wrote:
> On Sat, 2025-03-08 at 15:07 -0600, Bjorn Helgaas wrote:
> > On Sat, Mar 08, 2025 at 01:23:28PM +0300, Dan Carpenter wrote:
> > > Hello Philipp Stanner,
> > > 
> > > Commit ba10e5011d05 ("PCI: Check BAR index for validity") from Mar
> > > 4,
> > > 2025 (linux-next), leads to the following Smatch static checker
> > > warning:
> > > 
> > > 	drivers/pci/devres.c:632
> > > pcim_remove_bar_from_legacy_table()
> > > 	error: buffer overflow 'legacy_iomap_table' 6 <= 15
> > 
> > Thanks, I dropped this patch for now.
> > 
> > > drivers/pci/devres.c
> > >     621 static void pcim_remove_bar_from_legacy_table(struct
> > > pci_dev *pdev, int bar)
> > >     622 {
> > >     623         void __iomem **legacy_iomap_table;
> > >     624 
> > >     625         if (!pci_bar_index_is_valid(bar))
> > > 
> > > This line used to check PCI_STD_NUM_BARS (6) but now it's checking
> > > PCI_NUM_RESOURCES (15).
> 
> What is even going on here. Why are thos different values? Does a PCI
> device now have at most 6, or 15 BARs?

You included the link below, so I guess you found the answer to this,
but PCI devices can have:

  - up to six normal BARs (pci_dev.resource[0-5])

  - a ROM BAR (pci_dev.resource[6])

  - up to six SR-IOV BARs (pci_dev.resource[7-12])

  - four windows (for bridges) (pci_dev.resource[13-16])

> Or is a BAR different from a "resource"?

Yes, as above.  Not all can be used at once, e.g., bridges can only
have two BARs and may not implement all four windows, and SR-IOV VFs
can't use the normal BARs at all.

> And why would it be 15? I haven't read the standard, but I would
> suspect it should be 16.

This is an implementation thing, not a PCI spec thing, but I count a
maximum of 17 resources if CONFIG_PCI_IOV is defined.

> And which of those two here should be used?
> https://elixir.bootlin.com/linux/v6.14-rc4/source/include/linux/pci.h#L133