Re: [PATCH] vfio/pci: Sanity check IGD OpRegion Size

From: Yuan Yao
Date: Sun May 09 2021 - 21:11:20 EST


On Fri, May 07, 2021 at 12:53:17PM -0600, Alex Williamson wrote:
> The size field of the IGD OpRegion table is supposed to indicate table
> size in KB, but we've seen at least one report of a BIOS that appears
> to incorrectly report size in bytes. The default size is 8 (*1024 =
> 8KB), but an incorrect implementation may report 8192 (*1024 = 8MB)
> and can cause a variety of mapping errors.
>
> It's believed that 8MB would be an implausible, if not absurd, actual
> size, so we can probably be pretty safe in assuming this is a BIOS bug
> where the intended size is likely 8KB.
>
> Reported-by: Travis Faulhaber <tkffaul@xxxxxxxxxxx>
> Tested-by: Travis Faulhaber <tkffaul@xxxxxxxxxxx>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
> drivers/vfio/pci/vfio_pci_igd.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_igd.c b/drivers/vfio/pci/vfio_pci_igd.c
> index 228df565e9bc..c89a4797cd18 100644
> --- a/drivers/vfio/pci/vfio_pci_igd.c
> +++ b/drivers/vfio/pci/vfio_pci_igd.c
> @@ -86,7 +86,16 @@ static int vfio_pci_igd_opregion_init(struct vfio_pci_device *vdev)
> return -EINVAL;
> }
>
> - size *= 1024; /* In KB */
> + /*
> + * The OpRegion size field is specified as size in KB, but there have been
> + * user reports where this field appears to report size in bytes. If we
> + * read 8192, assume this is the case.
> + */
> + if (size == OPREGION_SIZE)

Is "size >= OPREGION_SIZE" or "size >= smaller but still implausible value
(like 4096)" better for covering more bad BIOS implementation cases ?

> + pci_warn(vdev->pdev,
> + "BIOS Bug, IGD OpRegion reports invalid size, assuming default 8KB\n");
> + else
> + size *= 1024; /* In KB */
>
> /*
> * Support opregion v2.1+
>
>