Message-ID: <2025061810-CVE-2022-50118-60c9@gregkh>
Date: Wed, 18 Jun 2025 13:03:03 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-50118: powerpc/perf: Optimize clearing the pending PMI and remove WARN_ON for PMI check in power_pmu_disable

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

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

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

powerpc/perf: Optimize clearing the pending PMI and remove WARN_ON for PMI check in power_pmu_disable

commit 2c9ac51b850d ("powerpc/perf: Fix PMU callbacks to clear
pending PMI before resetting an overflown PMC") added a new
function "pmi_irq_pending" in hw_irq.h. This function is to check
if there is a PMI marked as pending in Paca (PACA_IRQ_PMI).This is
used in power_pmu_disable in a WARN_ON. The intention here is to
provide a warning if there is PMI pending, but no counter is found
overflown.

During some of the perf runs, below warning is hit:

WARNING: CPU: 36 PID: 0 at arch/powerpc/perf/core-book3s.c:1332 power_pmu_disable+0x25c/0x2c0
 Modules linked in:
 -----

 NIP [c000000000141c3c] power_pmu_disable+0x25c/0x2c0
 LR [c000000000141c8c] power_pmu_disable+0x2ac/0x2c0
 Call Trace:
 [c000000baffcfb90] [c000000000141c8c] power_pmu_disable+0x2ac/0x2c0 (unreliable)
 [c000000baffcfc10] [c0000000003e2f8c] perf_pmu_disable+0x4c/0x60
 [c000000baffcfc30] [c0000000003e3344] group_sched_out.part.124+0x44/0x100
 [c000000baffcfc80] [c0000000003e353c] __perf_event_disable+0x13c/0x240
 [c000000baffcfcd0] [c0000000003dd334] event_function+0xc4/0x140
 [c000000baffcfd20] [c0000000003d855c] remote_function+0x7c/0xa0
 [c000000baffcfd50] [c00000000026c394] flush_smp_call_function_queue+0xd4/0x300
 [c000000baffcfde0] [c000000000065b24] smp_ipi_demux_relaxed+0xa4/0x100
 [c000000baffcfe20] [c0000000000cb2b0] xive_muxed_ipi_action+0x20/0x40
 [c000000baffcfe40] [c000000000207c3c] __handle_irq_event_percpu+0x8c/0x250
 [c000000baffcfee0] [c000000000207e2c] handle_irq_event_percpu+0x2c/0xa0
 [c000000baffcff10] [c000000000210a04] handle_percpu_irq+0x84/0xc0
 [c000000baffcff40] [c000000000205f14] generic_handle_irq+0x54/0x80
 [c000000baffcff60] [c000000000015740] __do_irq+0x90/0x1d0
 [c000000baffcff90] [c000000000016990] __do_IRQ+0xc0/0x140
 [c0000009732f3940] [c000000bafceaca8] 0xc000000bafceaca8
 [c0000009732f39d0] [c000000000016b78] do_IRQ+0x168/0x1c0
 [c0000009732f3a00] [c0000000000090c8] hardware_interrupt_common_virt+0x218/0x220

This means that there is no PMC overflown among the active events
in the PMU, but there is a PMU pending in Paca. The function
"any_pmc_overflown" checks the PMCs on active events in
cpuhw->n_events. Code snippet:

<<>>
if (any_pmc_overflown(cpuhw))
 	clear_pmi_irq_pending();
 else
 	WARN_ON(pmi_irq_pending());
<<>>

Here the PMC overflown is not from active event. Example: When we do
perf record, default cycles and instructions will be running on PMC6
and PMC5 respectively. It could happen that overflowed event is currently
not active and pending PMI is for the inactive event. Debug logs from
trace_printk:

<<>>
any_pmc_overflown: idx is 5: pmc value is 0xd9a
power_pmu_disable: PMC1: 0x0, PMC2: 0x0, PMC3: 0x0, PMC4: 0x0, PMC5: 0xd9a, PMC6: 0x80002011
<<>>

Here active PMC (from idx) is PMC5 , but overflown PMC is PMC6(0x80002011).
When we handle PMI interrupt for such cases, if the PMC overflown is
from inactive event, it will be ignored. Reference commit:
commit bc09c219b2e6 ("powerpc/perf: Fix finding overflowed PMC in interrupt")

Patch addresses two changes:
1) Fix 1 : Removal of warning ( WARN_ON(pmi_irq_pending()); )
   We were printing warning if no PMC is found overflown among active PMU
   events, but PMI pending in PACA. But this could happen in cases where
   PMC overflown is not in active PMC. An inactive event could have caused
   the overflow. Hence the warning is not needed. To know pending PMI is
   from an inactive event, we need to loop through all PMC's which will
   cause more SPR reads via mfspr and increase in context switch. Also in
   existing function: perf_event_interrupt, already we ignore PMI's
   overflown when it is from an inactive PMC.

2) Fix 2: optimization in clearing pending PMI.
   Currently we check for any active PMC overflown before clearing PMI
   pending in Paca. This is causing additional SPR read also. From point 1,
   we know that if PMI pending in Paca from inactive cases, that is going
   to be ignored during replay. Hence if there is pending PMI in Paca, just
   clear it irrespective of PMC overflown or not.

In summary, remove the any_pmc_overflown check entirely in
power_pmu_disable. ie If there is a pending PMI in Paca, clear it, since
we are in pmu_disable. There could be cases where PMI is pending because
of inactive PMC ( which later when replayed also will get ignored ), so
WARN_ON could give false warning. Hence removing it.

The Linux kernel CVE team has assigned CVE-2022-50118 to this issue.


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

	Issue introduced in 5.10.94 with commit ef798cd035f316a537fee8ed170c127f12407085 and fixed in 5.10.137 with commit 875b2bf469d094754ac2ba9af91dcd529eb12bf6
	Issue introduced in 5.15.17 with commit fadcafa3959281ce2d96feedece8c75c3f95f8a5 and fixed in 5.15.61 with commit 87b1a9175f08313f40fcb6d6dc536dbe451090eb
	Issue introduced in 5.17 with commit 2c9ac51b850d84ee496b0a5d832ce66d411ae552 and fixed in 5.18.18 with commit 0a24ea26c3278216642a43291df7976a73a0a7ee
	Issue introduced in 5.17 with commit 2c9ac51b850d84ee496b0a5d832ce66d411ae552 and fixed in 5.19.2 with commit 7e83af3dd4a3afca8f83ffde518cafd52f45b830
	Issue introduced in 5.17 with commit 2c9ac51b850d84ee496b0a5d832ce66d411ae552 and fixed in 6.0 with commit 890005a7d98f7452cfe86dcfb2aeeb7df01132ce
	Issue introduced in 5.16.3 with commit 215a90ce3754fe509efbce6b73a4bb643c7e7528

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-2022-50118
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/core-book3s.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/875b2bf469d094754ac2ba9af91dcd529eb12bf6
	https://git.kernel.org/stable/c/87b1a9175f08313f40fcb6d6dc536dbe451090eb
	https://git.kernel.org/stable/c/0a24ea26c3278216642a43291df7976a73a0a7ee
	https://git.kernel.org/stable/c/7e83af3dd4a3afca8f83ffde518cafd52f45b830
	https://git.kernel.org/stable/c/890005a7d98f7452cfe86dcfb2aeeb7df01132ce

Powered by blists - more mailing lists