In the Linux kernel, the following vulnerability has been resolved: vfio/pci: Latch disable_idle_d3 per device When disable_idle_d3 was in

In the Linux kernel, the following vulnerability has been resolved:

vfio/pci: Latch disable_idle_d3 per device

When disable_idle_d3 was introduced in vfio-pci, it directly manipulated
the device power state with pci_set_power_state(). There were no
refcounts to maintain or balanced operations, we could unconditionally
bring the device to D0 and conditionally move it to D3hot. Therefore
the module parameter was made writable.

Later, in commit c61302aa48f7 ("vfio/pci: Move module parameters to
vfio_pci.c"), as part of the vfio-pci-core split, the writable aspect
of the module parameter was nullified. The parameter value could still
be changed through sysfs, but the vfio-pci driver latched the values
into vfio-pci-core globals at module init. Loading the vfio-pci module,
or unloading and reloading, with non-default or different values could
change the globals relative to existing devices bound to vfio-pci
variant drivers.

Runtime PM was introduced in commit 7ab5e10eda02 ("vfio/pci: Move the
unused device into low power state with runtime PM"), which marks the
point where power states became refcounted. PM get and put operations
need to be balanced, but the same module operations noted above can
change the global variables relative to those devices already bound to
vfio-pci variant drivers. This introduces a window where PM operations
can now become unbalanced.

To resolve this with a narrow footprint for stable backports, the
disable_idle_d3 flag is latched into the vfio_pci_core_device at the
time of initialization, such that the device always operates with a
consistent value.

NB. vfio_pci_dev_set_try_reset() now unconditionally raises the
runtime PM usage count around bus reset to account for disable_idle_d3
becoming a per-device rather than global flag. When this flag is set,
the additional get/put pair is harmless and allows continued use of the
shared vfio_pci_dev_set_pm_runtime_get() helper.