powerpc/perf: Fix ref-counting on the PMU 'vpa_pmu'

JIRA: https://issues.redhat.com/browse/RHEL-77936

CVE: CVE-2025-22094

upstream
========
commit ff99d5b
Author: Vaibhav Jain <[email protected]>
Date: Tue Feb 4 21:05:26 2025 +0530

description
===========
Commit 176cda0 ("powerpc/perf: Add perf interface to expose vpa
counters") introduced 'vpa_pmu' to expose Book3s-HV nested APIv2 provided
L1<->L2 context switch latency counters to L1 user-space via
perf-events. However the newly introduced PMU named 'vpa_pmu' doesn't
assign ownership of the PMU to the module 'vpa_pmu'. Consequently the
module 'vpa_pmu' can be unloaded while one of the perf-events are still
active, which can lead to kernel oops and panic of the form below on a
Pseries-LPAR:

BUG: Kernel NULL pointer dereference on read at 0x00000058
<snip>
 NIP [c000000000506cb8] event_sched_out+0x40/0x258
 LR [c00000000050e8a4] __perf_remove_from_context+0x7c/0x2b0
 Call Trace:
 [c00000025fc3fc30] [c00000025f8457a8] 0xc00000025f8457a8 (unreliable)
 [c00000025fc3fc80] [fffffffffffffee0] 0xfffffffffffffee0
 [c00000025fc3fcd0] [c000000000501e70] event_function+0xa8/0x120
<snip>
 Kernel panic - not syncing: Aiee, killing interrupt handler!

Fix this by adding the module ownership to 'vpa_pmu' so that the module
'vpa_pmu' is ref-counted and prevented from being unloaded when perf-events
are initialized.

Fixes: 176cda0 ("powerpc/perf: Add perf interface to expose vpa counters")
    Signed-off-by: Vaibhav Jain <[email protected]>
    Signed-off-by: Madhavan Srinivasan <[email protected]>
    Link: https://patch.msgid.link/[email protected]

Signed-off-by: Michael Petlan <[email protected]>

Author: rfmvh

arch/powerpc/perf/vpa-pmu.c

@@ -156,6 +156,7 @@ static void vpa_pmu_del(struct perf_event *event, int flags)
 }
 
 static struct pmu vpa_pmu = {
+	.module		= THIS_MODULE,
 	.task_ctx_nr	= perf_sw_context,
 	.name		= "vpa_pmu",
 	.event_init	= vpa_pmu_event_init,