[Patch v2 3/6] perf/x86: Check if cpuc->events[*] pointer exists before accessing it

[Dapeng Mi <dapeng1.mi@linux.intel.com>]

The PMI handler could disable some events as the interrupt throttling
and clear the corresponding items in cpuc->events[] array.

perf_event_overflow()
  -> __perf_event_overflow()
    ->__perf_event_account_interrupt()
      -> perf_event_throttle_group()
        -> perf_event_throttle()
          -> event->pmu->stop()
            -> x86_pmu_stop()

Moreover PMI is NMI on x86 platform and it could interrupt other perf
code like setup_pebs_adaptive_sample_data(). So once PMI handling
finishes and returns into setup_pebs_adaptive_sample_data() and it could
find the cpuc->events[*] becomes NULL and accessing this NULL pointer
triggers an invalid memory access and leads to kernel crashes eventually.

Thus add NULL check before accessing cpuc->events[*] pointer.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202507042103.a15d2923-lkp@intel.com
Fixes: 9734e25fbf5a ("perf: Fix the throttle logic for a group")
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: kernel test robot <oliver.sang@intel.com>
---
 arch/x86/events/core.c       |  3 +++
 arch/x86/events/intel/core.c |  6 +++++-
 arch/x86/events/intel/ds.c   | 13 ++++++-------
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 7610f26dfbd9..f0a3bc57157d 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1711,6 +1711,9 @@ int x86_pmu_handle_irq(struct pt_regs *regs)
 			continue;
 
 		event = cpuc->events[idx];
+		if (!event)
+			continue;
+
 		last_period = event->hw.last_period;
 
 		val = static_call(x86_pmu_update)(event);
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 15da60cf69f2..386717b75a09 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2718,6 +2718,8 @@ static void update_saved_topdown_regs(struct perf_event *event, u64 slots,
 		if (!is_topdown_idx(idx))
 			continue;
 		other = cpuc->events[idx];
+		if (!other)
+			continue;
 		other->hw.saved_slots = slots;
 		other->hw.saved_metric = metrics;
 	}
@@ -2761,6 +2763,8 @@ static u64 intel_update_topdown_event(struct perf_event *event, int metric_end,
 		if (!is_topdown_idx(idx))
 			continue;
 		other = cpuc->events[idx];
+		if (!other)
+			continue;
 		__icl_update_topdown_event(other, slots, metrics,
 					   event ? event->hw.saved_slots : 0,
 					   event ? event->hw.saved_metric : 0);
@@ -3138,7 +3142,7 @@ static void x86_pmu_handle_guest_pebs(struct pt_regs *regs,
 
 	for_each_set_bit(bit, (unsigned long *)&guest_pebs_idxs, X86_PMC_IDX_MAX) {
 		event = cpuc->events[bit];
-		if (!event->attr.precise_ip)
+		if (!event || !event->attr.precise_ip)
 			continue;
 
 		perf_sample_data_init(data, 0, event->hw.last_period);
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index c0b7ac1c7594..b23c49e2e06f 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -2480,6 +2480,8 @@ static void intel_pmu_pebs_event_update_no_drain(struct cpu_hw_events *cpuc, u64
 	 */
 	for_each_set_bit(bit, (unsigned long *)&pebs_enabled, X86_PMC_IDX_MAX) {
 		event = cpuc->events[bit];
+		if (!event)
+			continue;
 		if (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)
 			intel_pmu_save_and_restart_reload(event, 0);
 	}
@@ -2579,10 +2581,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d
 			continue;
 
 		event = cpuc->events[bit];
-		if (WARN_ON_ONCE(!event))
-			continue;
-
-		if (WARN_ON_ONCE(!event->attr.precise_ip))
+		if (!event || WARN_ON_ONCE(!event->attr.precise_ip))
 			continue;
 
 		/* log dropped samples number */
@@ -2645,9 +2644,7 @@ static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_d
 		pebs_status = basic->applicable_counters & cpuc->pebs_enabled & mask;
 		for_each_set_bit(bit, (unsigned long *)&pebs_status, X86_PMC_IDX_MAX) {
 			event = cpuc->events[bit];
-
-			if (WARN_ON_ONCE(!event) ||
-			    WARN_ON_ONCE(!event->attr.precise_ip))
+			if (!event || WARN_ON_ONCE(!event->attr.precise_ip))
 				continue;
 
 			if (counts[bit]++) {
@@ -2663,6 +2660,8 @@ static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_d
 			continue;
 
 		event = cpuc->events[bit];
+		if (!event)
+			continue;
 
 		__intel_pmu_pebs_last_event(event, iregs, regs, data, last[bit],
 					    counts[bit], setup_pebs_adaptive_sample_data);
-- 
2.34.1