vfio/pci: Make VFIO_PCI_OFFSET_TO_INDEX() return unsigned

VFIO_PCI_OFFSET_TO_INDEX() is used in several places with a signed
parameter (e.g. loff_t).  Because it makes no sense for a BAR/resource
index to be negative, enforce this in the macro.

This fixes at least one current issue, where vfio_pci_ioeventfd() uses
this macro with an unvalidated signed loff_t returned into a signed
type, leading to a possible negative array access.  This instance does
test against an out-of-bounds positive value, so treating the index as
unsigned fixes this issue.

Fixes: 89e1f7d4c66d8 ("vfio: Add PCI device driver")
Signed-off-by: Matt Evans <mattev@meta.com>
Link: https://lore.kernel.org/r/20260511144642.2926799-1-mattev@meta.com
Signed-off-by: Alex Williamson <alex@shazbot.org>

diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 2ebba746c18f7bcadb3df0d93b76a94169dbfeba..89165b769e5c168a043bece8b995702627067002 100644 (file)
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -21,7 +21,7 @@
 #define VFIO_PCI_CORE_H
 
 #define VFIO_PCI_OFFSET_SHIFT   40
-#define VFIO_PCI_OFFSET_TO_INDEX(off)  (off >> VFIO_PCI_OFFSET_SHIFT)
+#define VFIO_PCI_OFFSET_TO_INDEX(off)  ((u64)(off) >> VFIO_PCI_OFFSET_SHIFT)
 #define VFIO_PCI_INDEX_TO_OFFSET(index)        ((u64)(index) << VFIO_PCI_OFFSET_SHIFT)
 #define VFIO_PCI_OFFSET_MASK   (((u64)(1) << VFIO_PCI_OFFSET_SHIFT) - 1)