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

Bjorn Helgaas
2020-11-03T21:28:50Z

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.

But if you want it,

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: linux-mm@kvack.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-samsung-soc@vger.kernel.org
> Cc: linux-media@vger.kernel.org
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: linux-pci@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> --
> v2: Improve commit message (Bjorn)
> ---
> drivers/pci/proc.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> index d35186b01d98..3a2f90beb4cb 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -274,6 +274,11 @@ static int proc_bus_pci_mmap(struct file *file, struct vm_area_struct *vma)
> else
> return -EINVAL;
> }
> +
> + if (dev->resource[i].flags & IORESOURCE_MEM &&
> + iomem_is_exclusive(dev->resource[i].start))
> + return -EINVAL;
> +
> ret = pci_mmap_page_range(dev, i, vma,
> fpriv->mmap_state, write_combine);
> if (ret < 0)
> --
> 2.28.0
>