CVE-2026-80727: x86/mce: Set up the polling timer before CMCI discovery

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

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

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

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

x86/mce: Set up the polling timer before CMCI discovery

I hit the following on one of my machines:

  mce: CPU0 BANK15 CMCI inherited storm
  ------------[ cut here ]------------
  ODEBUG: assert_init not available (active state 0) object: (____ptrval____) object type: timer_list hint: 0x0
  WARNING: lib/debugobjects.c:632 at debug_object_assert_init+0x178/0x230, CPU#0: swapper/0/0
  CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 7.2.0-rc5 #3 PREEMPTLAZY
  RIP: 0010:debug_object_assert_init+0x18f/0x230
  Call Trace:
   <TASK>
   __mod_timer
   mce_timer_kick
   cmci_discover
   intel_init_cmci
   mce_intel_feature_init
   mcheck_cpu_init
   identify_cpu
   identify_boot_cpu
   arch_cpu_finalize_init
   start_kernel

A second splat follows right after, from timer_setup() finding that same
timer already queued:

  ODEBUG: init active (active state 0) object: (____ptrval____) object type: timer_list hint: stub_timer+0x0/0x10

This is happening because CMCI storm detection is trying to modify the timer
before latter was properly set up.

Set up the timer first. __mcheck_cpu_setup_timer() only calls timer_setup(),
and depends on neither the generic nor the vendor init.

  [ bp: Massage commit message. ]

The Linux kernel CVE team has assigned CVE-2026-80727 to this issue.


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

	Issue introduced in 6.8 with commit 1f68ce2a027250aeeb1756391110cdc4dc97c797 and fixed in 6.12.105 with commit 17ab68d0cf6a41bff61b1e13c6141d9e463736ae
	Issue introduced in 6.8 with commit 1f68ce2a027250aeeb1756391110cdc4dc97c797 and fixed in 6.18.45 with commit e708fc1566ebd4a2d3f2546e6310d64d362db80d
	Issue introduced in 6.8 with commit 1f68ce2a027250aeeb1756391110cdc4dc97c797 and fixed in 7.1.9 with commit 4f4cba3947d2f0eceb32727e198ca2c149a653a9
	Issue introduced in 6.8 with commit 1f68ce2a027250aeeb1756391110cdc4dc97c797 and fixed in 7.2 with commit a213dfaa2596c1c0dc4dae91c14fbfa499c03223

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-2026-80727
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/cpu/mce/core.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/17ab68d0cf6a41bff61b1e13c6141d9e463736ae
	https://git.kernel.org/stable/c/e708fc1566ebd4a2d3f2546e6310d64d362db80d
	https://git.kernel.org/stable/c/4f4cba3947d2f0eceb32727e198ca2c149a653a9
	https://git.kernel.org/stable/c/a213dfaa2596c1c0dc4dae91c14fbfa499c03223