Subject: CVE-2024-31076: genirq/cpuhotplug, x86/vector: Prevent vector leak during CPU offline

From: Greg Kroah-Hartman <[email-masked]>

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

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

genirq/cpuhotplug, x86/vector: Prevent vector leak during CPU offline

The absence of IRQD_MOVE_PCNTXT prevents immediate effectiveness of
interrupt affinity reconfiguration via procfs. Instead, the change is
deferred until the next instance of the interrupt being triggered on the
original CPU.

When the interrupt next triggers on the original CPU, the new affinity is
enforced within __irq_move_irq(). A vector is allocated from the new CPU,
but the old vector on the original CPU remains and is not immediately
reclaimed. Instead, apicd->move_in_progress is flagged, and the reclaiming
process is delayed until the next trigger of the interrupt on the new CPU.

Upon the subsequent triggering of the interrupt on the new CPU,
irq_complete_move() adds a task to the old CPU's vector_cleanup list if it
remains online. Subsequently, the timer on the old CPU iterates over its
vector_cleanup list, reclaiming old vectors.

However, a rare scenario arises if the old CPU is outgoing before the
interrupt triggers again on the new CPU.

In that case irq_force_complete_move() is not invoked on the outgoing CPU
to reclaim the old apicd->prev_vector because the interrupt isn't currently
affine to the outgoing CPU, and irq_needs_fixup() returns false. Even
though __vector_schedule_cleanup() is later called on the new CPU, it
doesn't reclaim apicd->prev_vector; instead, it simply resets both
apicd->move_in_progress and apicd->prev_vector to 0.

As a result, the vector remains unreclaimed in vector_matrix, leading to a
CPU vector leak.

To address this issue, move the invocation of irq_force_complete_move()
before the irq_needs_fixup() call to reclaim apicd->prev_vector, if the
interrupt is currently or used to be affine to the outgoing CPU.

Additionally, reclaim the vector in __vector_schedule_cleanup() as well,
following a warning message, although theoretically it should never see
apicd->move_in_progress with apicd->prev_cpu pointing to an offline CPU.

The Linux kernel CVE team has assigned CVE-2024-31076 to this issue.

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

	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 4.19.316 with commit a40209d355af
	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 5.4.278 with commit f5f467596060
	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 5.10.219 with commit 6752dfcfff3a
	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 5.15.161 with commit 9eeda3e0071a
	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 6.1.93 with commit e9c96d01d520
	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 6.6.33 with commit 59f86a290838
	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 6.9.4 with commit ebfb16fc057a
	Issue introduced in 4.13 with commit f0383c24b485 and fixed in 6.10 with commit a6c11c0a5235

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-2024-31076
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:
	arch/x86/kernel/apic/vector.c
	kernel/irq/cpuhotplug.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/a40209d355afe4ed6d533507838c9e5cd70a76d8
	https://git.kernel.org/stable/c/f5f4675960609d8c5ee95f027fbf6ce380f98372
	https://git.kernel.org/stable/c/6752dfcfff3ac3e16625ebd3f0ad9630900e7e76
	https://git.kernel.org/stable/c/9eeda3e0071a329af1eba15f4e57dc39576bb420
	https://git.kernel.org/stable/c/e9c96d01d520498b169ce734a8ad1142bef86a30
	https://git.kernel.org/stable/c/59f86a2908380d09cdc726461c0fbb8d8579c99f
	https://git.kernel.org/stable/c/ebfb16fc057a016abb46a9720a54abf0d4f6abe1
	https://git.kernel.org/stable/c/a6c11c0a5235fb144a65e0cb2ffd360ddc1f6c32