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

From: Alex Williamson
Date: Fri May 07 2021 - 14:53:24 EST


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

/*
* Support opregion v2.1+