CVE-2026-64070: powerpc/hv-gpci: fix preempt count leak in sysfs show paths

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

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

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

powerpc/hv-gpci: fix preempt count leak in sysfs show paths

Four sysfs show() callbacks in hv-gpci take get_cpu_var(hv_gpci_reqb)
(which calls preempt_disable()) but only call the matching put_cpu_var()
on the error path under the 'out:' label. Every successful read leaks
one preempt_disable():

  processor_bus_topology_show()
  processor_config_show()
  affinity_domain_via_virtual_processor_show()
  affinity_domain_via_domain_show()

(affinity_domain_via_partition_show() was already correct.)

On a CONFIG_PREEMPT=y kernel, repeated reads raise preempt_count and
eventually return to userspace with preemption still disabled. The
next user-mode page fault then hits faulthandler_disabled() == 1,
gets forced to SIGSEGV, and the resulting coredump trips
'BUG: scheduling while atomic' in call_usermodehelper_exec ->
wait_for_completion_state -> schedule:

  BUG: scheduling while atomic: <task>/<pid>/0x00000004
  ...
  __schedule_bug+0x6c/0x90
  __schedule+0x58c/0x13a0
  schedule+0x48/0x1a0
  schedule_timeout+0x104/0x170
  wait_for_completion_state+0x16c/0x330
  call_usermodehelper_exec+0x254/0x2d0
  vfs_coredump+0x1050/0x2590
  get_signal+0xb9c/0xc80
  do_notify_resume+0xf8/0x470

Add an out_success label that calls put_cpu_var() before returning
the byte count, mirroring affinity_domain_via_partition_show().

The Linux kernel CVE team has assigned CVE-2026-64070 to this issue.


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

	Issue introduced in 6.6 with commit 71f1c39647d8c9d4d54a861ec81f1ff17544bcb6 and fixed in 7.0.11 with commit 903409000a07ac8e31ffedeb8516f4f8d67150c8
	Issue introduced in 6.6 with commit 71f1c39647d8c9d4d54a861ec81f1ff17544bcb6 and fixed in 7.1 with commit dbc30a57bd8e026995e9fa8e8c31cffd18542c01

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-2026-64070
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/powerpc/perf/hv-gpci.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/903409000a07ac8e31ffedeb8516f4f8d67150c8
	https://git.kernel.org/stable/c/dbc30a57bd8e026995e9fa8e8c31cffd18542c01