Re: [PATCH v5 11/15] PCI: Obey iomem restrictions for procfs mmap

Dan Williams
2020-11-03T22:09:51Z

On Tue, Nov 3, 2020 at 1:28 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Fri, Oct 30, 2020 at 11:08:11AM +0100, Daniel Vetter wrote:
> > There's three ways to access PCI BARs from userspace: /dev/mem, sysfs
> > files, and the old proc interface. Two check against
> > iomem_is_exclusive, proc never did. And with CONFIG_IO_STRICT_DEVMEM,
> > this starts to matter, since we don't want random userspace having
> > access to PCI BARs while a driver is loaded and using it.
> >
> > Fix this by adding the same iomem_is_exclusive() check we already have
> > on the sysfs side in pci_mmap_resource().
> >
> > References: 90a545e98126 ("restrict /dev/mem to idle io memory ranges")
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>
> This is OK with me but it looks like IORESOURCE_EXCLUSIVE is currently
> only used in a few places:
>
> e1000_probe() calls pci_request_selected_regions_exclusive(),
> ne_pci_probe() calls pci_request_regions_exclusive(),
> vmbus_allocate_mmio() calls request_mem_region_exclusive()
>
> which raises the question of whether it's worth keeping
> IORESOURCE_EXCLUSIVE at all. I'm totally fine with removing it
> completely.

Now that CONFIG_IO_STRICT_DEVMEM upgrades IORESOURCE_BUSY to
IORESOURCE_EXCLUSIVE semantics the latter has lost its meaning so I'd
be in favor of removing it as well.