CVE-2026-89589: acpi/apei/ghes: Use raw_spinlock_t for CXL CPER work locks

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

acpi/apei/ghes: Use raw_spinlock_t for CXL CPER work locks

The CXL CPER work registration and unregistration helpers acquire
cxl_cper_work_lock and cxl_cper_prot_err_work_lock with a spinlock
guard(), which leaves local interrupts enabled. The corresponding post
paths (cxl_cper_post_event(), cxl_cper_post_prot_err()) execute in hard
IRQ context (they are called from the GHES error notification path) and
acquire the same locks with an irqsave guard().

If a CPU is holding one of these locks via a spinlock guard() when a GHES
interrupt arrives on the same CPU, the IRQ handler spins on the held lock
waiting for it to release, while the lock holder is preempted by the IRQ.
The result is a deadlock.

Convert both locks from spinlock_t to raw_spinlock_t and use guard() at
all call sites. On PREEMPT_RT kernels spinlock_t is backed by rt_mutex and
sleeping from hard IRQ context is not permitted; raw_spinlock_t is safe in
both contexts.

Add WARN_ONCE to both register functions to surface double-registration
bugs at runtime.

Restructure both unregister functions to clear the global work pointer
under the lock before calling cancel_work_sync(), closing the window
where a CPER interrupt could schedule work on a pointer about to be
freed. Add kfifo_reset() after cancel_work_sync() so stale entries
are not replayed on next module load.

Both kfifos are single-consumer: only one work_struct is registered at
a time, enforced by the WARN_ONCE guard in the register functions.
kfifo_reset() is safe outside the lock because cancel_work_sync() has
already quiesced the consumer, and no new consumer can register until
the current module exit completes and a fresh module init runs.

Remove the redundant cancel_work_sync() call from cxl_ras_exit() and
cxl_pci_driver_exit(). The CPER unregister functions now quiesce
the work internally.

The Linux kernel CVE team has assigned CVE-2026-89589 to this issue.


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

	Issue introduced in 6.10 with commit 5e4a264bf8b55d5a1b4c8cd96ac10b99f98d7487 and fixed in 6.18.50 with commit c735dbce7ad03df708bf22ec964f67e43cbc823a
	Issue introduced in 6.10 with commit 5e4a264bf8b55d5a1b4c8cd96ac10b99f98d7487 and fixed in 7.2.4 with commit 0e25382b05de48d09b243d3d447d236a6d735bc2
	Issue introduced in 6.10 with commit 5e4a264bf8b55d5a1b4c8cd96ac10b99f98d7487 and fixed in 7.3-rc1 with commit 6625ca499c3131ef63be3215f8f942d7a097ea3a

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-2026-89589
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/acpi/apei/ghes.c
	drivers/cxl/core/ras.c
	drivers/cxl/pci.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/c735dbce7ad03df708bf22ec964f67e43cbc823a
	https://git.kernel.org/stable/c/0e25382b05de48d09b243d3d447d236a6d735bc2
	https://git.kernel.org/stable/c/6625ca499c3131ef63be3215f8f942d7a097ea3a