[Patch v2 3/7] perf/x86: Guard intel_pmu_cpu_dead() against invalid hybrid PMU casts

[Dapeng Mi]

In failure paths, cpuc->pmu can still point to the global static pmu
instead of an embedded x86_hybrid_pmu::pmu. Calling hybrid_pmu() on
that pointer causes an invalid container conversion and may lead to
out-of-bounds access.

This can happen in at least two cases:
- init_hybrid_pmu() fails check_hw_exists() and leaves cpuc->pmu as-is.
- CPU hotplug fails between CPUHP_PERF_X86_PREPARE and
CPUHP_AP_PERF_X86_STARTING, and rollback invokes intel_pmu_cpu_dead().

Fix both paths by:
- Clear cpuc->pmu to NULL when check_hw_exists() fails.
- Validat that cpuc->pmu is not the global static pmu before calling
  hybrid_pmu() in intel_pmu_cpu_dead().

A new helper x86_get_static_pmu() is added to get the global static pmu.

Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
---
 arch/x86/events/core.c       | 5 +++++
 arch/x86/events/intel/core.c | 7 +++++--
 arch/x86/events/perf_event.h | 1 +
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 6c63b27e11e6..a02f303a9151 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -790,6 +790,11 @@ int is_x86_event(struct perf_event *event)
 	return false;
 }
 
+inline struct pmu *x86_get_static_pmu(void)
+{
+	return &pmu;
+}
+
 struct pmu *x86_get_pmu(unsigned int cpu)
 {
 	struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index b39c6ce0efb5..a991fc4f1575 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -6329,8 +6329,10 @@ static bool init_hybrid_pmu(int cpu)
 
 	intel_pmu_check_hybrid_pmus(pmu);
 
-	if (!check_hw_exists(&pmu->pmu, pmu->cntr_mask, pmu->fixed_cntr_mask))
+	if (!check_hw_exists(&pmu->pmu, pmu->cntr_mask, pmu->fixed_cntr_mask)) {
+		cpuc->pmu = NULL;
 		return false;
+	}
 
 	pr_info("%s PMU driver: ", pmu->name);
 
@@ -6475,11 +6477,12 @@ void intel_cpuc_finish(struct cpu_hw_events *cpuc)
 static void intel_pmu_cpu_dead(int cpu)
 {
 	struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
+	struct pmu *pmu = x86_get_static_pmu();
 
 	release_arch_pebs_buf_on_cpu(cpu);
 	intel_cpuc_finish(cpuc);
 
-	if (is_hybrid() && cpuc->pmu)
+	if (is_hybrid() && cpuc->pmu && cpuc->pmu != pmu)
 		cpumask_clear_cpu(cpu, &hybrid_pmu(cpuc->pmu)->supported_cpus);
 }
 
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index a8afea8d38f0..01ae287cde16 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1161,6 +1161,7 @@ static struct perf_pmu_format_hybrid_attr format_attr_hybrid_##_name = {\
 	.pmu_type	= _pmu,						\
 }
 
+struct pmu *x86_get_static_pmu(void);
 struct pmu *x86_get_pmu(unsigned int cpu);
 extern struct x86_pmu x86_pmu __read_mostly;
 
-- 
2.34.1