Commit-ID: 472de49fdc53365c880ab81ae2b5cfdd83db0b06 Gitweb: https://git.kernel.org/tip/472de49fdc53365c880ab81ae2b5cfdd83db0b06 Author: Jiri Olsa jolsa@kernel.org AuthorDate: Wed, 21 Nov 2018 11:16:12 +0100 Committer: Ingo Molnar mingo@kernel.org CommitDate: Thu, 22 Nov 2018 09:45:10 +0100

perf/x86/intel: Disallow precise_ip on BTS events

Vince reported a crash in the BTS flush code when touching the callchain data, which was supposed to be initialized as an 'early' callchain, but intel_pmu_drain_bts_buffer() does not do that:

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 but can be easily reproduced by:

# perf record -e cpu/branch-instructions/pu -g -c 1

Peter suggested not to allow branch tracing for precise events:

Now arguably, this is really stupid behaviour. Who in his right mind wants callchain output on BTS entries. And even if they do, BTS + precise_ip is nonsensical.

So in my mind disallowing precise_ip on BTS would be the simplest fix.

Suggested-by: Peter Zijlstra peterz@infradead.org Reported-by: Vince Weaver vincent.weaver@maine.edu Signed-off-by: Jiri Olsa jolsa@kernel.org Acked-by: Peter Zijlstra a.p.zijlstra@chello.nl Cc: stable@vger.kernel.org Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Arnaldo Carvalho de Melo acme@kernel.org Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Jiri Olsa jolsa@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Stephane Eranian eranian@google.com Cc: Thomas Gleixner tglx@linutronix.de Fixes: 6cbc304f2f36 ("perf/x86/intel: Fix unwind errors from PEBS entries (mk-II)") Link: http://lkml.kernel.org/r/20181121101612.16272-3-jolsa@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org --- arch/x86/events/intel/core.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index a15a73788693..ecc3e34ca955 100644 --- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -3106,6 +3106,10 @@ static int intel_pmu_bts_config(struct perf_event *event) if (!attr->exclude_kernel) return -EOPNOTSUPP;

+ /* BTS is not allowed for precise events. */ + if (attr->precise_ip) + return -EOPNOTSUPP; + /* disallow bts if conflicting events are present */ if (x86_add_exclusive(x86_lbr_exclusive_lbr)) return -EBUSY;