CVE-2024-26812: vfio/pci: Create persistent INTx handler

CVE-2024-26812: vfio/pci: Create persistent INTx handler

[Greg Kroah-Hartman]

Description
===========

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

vfio/pci: Create persistent INTx handler

A vulnerability exists where the eventfd for INTx signaling can be
deconfigured, which unregisters the IRQ handler but still allows
eventfds to be signaled with a NULL context through the SET_IRQS ioctl
or through unmask irqfd if the device interrupt is pending.

Ideally this could be solved with some additional locking; the igate
mutex serializes the ioctl and config space accesses, and the interrupt
handler is unregistered relative to the trigger, but the irqfd path
runs asynchronous to those.  The igate mutex cannot be acquired from the
atomic context of the eventfd wake function.  Disabling the irqfd
relative to the eventfd registration is potentially incompatible with
existing userspace.

As a result, the solution implemented here moves configuration of the
INTx interrupt handler to track the lifetime of the INTx context object
and irq_type configuration, rather than registration of a particular
trigger eventfd.  Synchronization is added between the ioctl path and
eventfd_signal() wrapper such that the eventfd trigger can be
dynamically updated relative to in-flight interrupts or irqfd callbacks.

The Linux kernel CVE team has assigned CVE-2024-26812 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.6 with commit 89e1f7d4c66d and fixed in 6.1.84 with commit 7d29d4c72c1e
	Issue introduced in 3.6 with commit 89e1f7d4c66d and fixed in 6.6.24 with commit 69276a555c74
	Issue introduced in 3.6 with commit 89e1f7d4c66d and fixed in 6.7.12 with commit 4c089cefe309
	Issue introduced in 3.6 with commit 89e1f7d4c66d and fixed in 6.8.3 with commit 0e09cf81959d
	Issue introduced in 3.6 with commit 89e1f7d4c66d and fixed in 6.9-rc1 with commit 18c198c96a81

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-26812
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/vfio/pci/vfio_pci_intrs.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/7d29d4c72c1e196cce6969c98072a272d1a703b3
	https://git.kernel.org/stable/c/69276a555c740acfbff13fb5769ee9c92e1c828e
	https://git.kernel.org/stable/c/4c089cefe30924fbe20dd1ee92774ea1f5eca834
	https://git.kernel.org/stable/c/0e09cf81959d9f12b75ad5c6dd53d237432ed034
	https://git.kernel.org/stable/c/18c198c96a815c962adc2b9b77909eec0be7df4d