Messages in this thread Patch in this message | | | From | Jiri Olsa <> | Subject | [PATCH] perf/x86/intel: Init early callchain for bts event | Date | Sun, 11 Nov 2018 19:16:50 +0100 |
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Vince reported crash in bts flush code when touching the callchain data, which was supposed to be initialized as an 'early' callchain data.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 ... Call Trace: <IRQ> intel_pmu_drain_bts_buffer+0x151/0x220 ? intel_get_event_constraints+0x219/0x360 ? perf_assign_events+0xe2/0x2a0 ? select_idle_sibling+0x22/0x3a0 ? __update_load_avg_se+0x1ec/0x270 ? enqueue_task_fair+0x377/0xdd0 ? cpumask_next_and+0x19/0x20 ? load_balance+0x134/0x950 ? check_preempt_curr+0x7a/0x90 ? ttwu_do_wakeup+0x19/0x140 x86_pmu_stop+0x3b/0x90 x86_pmu_del+0x57/0x160 event_sched_out.isra.106+0x81/0x170 group_sched_out.part.108+0x51/0xc0 __perf_event_disable+0x7f/0x160 event_function+0x8c/0xd0 remote_function+0x3c/0x50 flush_smp_call_function_queue+0x35/0xe0 smp_call_function_single_interrupt+0x3a/0xd0 call_function_single_interrupt+0xf/0x20 </IRQ>
It was triggered by fuzzer by can be easilt reproduced by: # perf record -e cpu/branch-instructions/p -g -c 1
The problem is that bts drain code does not initialize sample's early callchain data and calls perf_prepare_sample with NULL sample->callchain, even if it's expected to exist via __PERF_SAMPLE_CALLCHAIN_EARLY sample type bit.
The fix initializes the callchain data for this case with empty callchain, because bts does not report callchains.
Cc: Vince Weaver <vincent.weaver@maine.edu> Fixes: 6cbc304f2f36 ("perf/x86/intel: Fix unwind errors from PEBS entries (mk-II)") Reported-by: Vince Weaver <vincent.weaver@maine.edu> Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- arch/x86/events/intel/ds.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index b7b01d762d32..1049b547fdfe 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -577,6 +577,8 @@ void intel_pmu_disable_bts(void) update_debugctlmsr(debugctlmsr); } +static struct perf_callchain_entry __empty_callchain = { .nr = 0, }; + int intel_pmu_drain_bts_buffer(void) { struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); @@ -612,6 +614,9 @@ int intel_pmu_drain_bts_buffer(void) perf_sample_data_init(&data, 0, event->hw.last_period); + if (event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY) + data.callchain = &__empty_callchain; + /* * BTS leaks kernel addresses in branches across the cpl boundary, * such as traps or system calls, so unless the user is asking for -- 2.17.2
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