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Subject[tip:perf/urgent] ftrace, perf: Avoid infinite event generation loop
Commit-ID:  d5b5f391d434c5cc8bcb1ab2d759738797b85f52
Gitweb: http://git.kernel.org/tip/d5b5f391d434c5cc8bcb1ab2d759738797b85f52
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 14 Nov 2013 16:23:04 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 19 Nov 2013 16:57:40 +0100

ftrace, perf: Avoid infinite event generation loop

Vince's perf-trinity fuzzer found yet another 'interesting' problem.

When we sample the irq_work_exit tracepoint with period==1 (or
PERF_SAMPLE_PERIOD) and we add an fasync SIGNAL handler we create an
infinite event generation loop:

,-> <IPI>
| irq_work_exit() ->
| trace_irq_work_exit() ->
| ...
| __perf_event_overflow() -> (due to fasync)
| irq_work_queue() -> (irq_work_list must be empty)
'--------- arch_irq_work_raise()

Similar things can happen due to regular poll() wakeups if we exceed
the ring-buffer wakeup watermark, or have an event_limit.

To avoid this, dis-allow sampling this particular tracepoint.

In order to achieve this, create a special perf_perm function pointer
for each event and call this (when set) on trying to create a
tracepoint perf event.

[ roasted: use expr... to allow for ',' in your expression ]

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Tested-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20131114152304.GC5364@laptop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/trace/irq_vectors.h | 11 +++++++++++
include/linux/ftrace_event.h | 16 ++++++++++++++++
include/linux/tracepoint.h | 4 ++++
include/trace/ftrace.h | 7 +++++++
kernel/trace/trace_event_perf.c | 6 ++++++
5 files changed, 44 insertions(+)

diff --git a/arch/x86/include/asm/trace/irq_vectors.h b/arch/x86/include/asm/trace/irq_vectors.h
index 2874df2..4cab890 100644
--- a/arch/x86/include/asm/trace/irq_vectors.h
+++ b/arch/x86/include/asm/trace/irq_vectors.h
@@ -72,6 +72,17 @@ DEFINE_IRQ_VECTOR_EVENT(x86_platform_ipi);
DEFINE_IRQ_VECTOR_EVENT(irq_work);

/*
+ * We must dis-allow sampling irq_work_exit() because perf event sampling
+ * itself can cause irq_work, which would lead to an infinite loop;
+ *
+ * 1) irq_work_exit happens
+ * 2) generates perf sample
+ * 3) generates irq_work
+ * 4) goto 1
+ */
+TRACE_EVENT_PERF_PERM(irq_work_exit, is_sampling_event(p_event) ? -EPERM : 0);
+
+/*
* call_function - called when entering/exiting a call function interrupt
* vector handler
*/
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 9abbe63..8c9b7a1 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -248,6 +248,9 @@ struct ftrace_event_call {
#ifdef CONFIG_PERF_EVENTS
int perf_refcount;
struct hlist_head __percpu *perf_events;
+
+ int (*perf_perm)(struct ftrace_event_call *,
+ struct perf_event *);
#endif
};

@@ -317,6 +320,19 @@ struct ftrace_event_file {
} \
early_initcall(trace_init_flags_##name);

+#define __TRACE_EVENT_PERF_PERM(name, expr...) \
+ static int perf_perm_##name(struct ftrace_event_call *tp_event, \
+ struct perf_event *p_event) \
+ { \
+ return ({ expr; }); \
+ } \
+ static int __init trace_init_perf_perm_##name(void) \
+ { \
+ event_##name.perf_perm = &perf_perm_##name; \
+ return 0; \
+ } \
+ early_initcall(trace_init_perf_perm_##name);
+
#define PERF_MAX_TRACE_SIZE 2048

#define MAX_FILTER_STR_VAL 256 /* Should handle KSYM_SYMBOL_LEN */
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index ebeab36..f16dc0a 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -267,6 +267,8 @@ static inline void tracepoint_synchronize_unregister(void)

#define TRACE_EVENT_FLAGS(event, flag)

+#define TRACE_EVENT_PERF_PERM(event, expr...)
+
#endif /* DECLARE_TRACE */

#ifndef TRACE_EVENT
@@ -399,4 +401,6 @@ static inline void tracepoint_synchronize_unregister(void)

#define TRACE_EVENT_FLAGS(event, flag)

+#define TRACE_EVENT_PERF_PERM(event, expr...)
+
#endif /* ifdef TRACE_EVENT (see note above) */
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 52594b2..6b852f6 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -90,6 +90,10 @@
#define TRACE_EVENT_FLAGS(name, value) \
__TRACE_EVENT_FLAGS(name, value)

+#undef TRACE_EVENT_PERF_PERM
+#define TRACE_EVENT_PERF_PERM(name, expr...) \
+ __TRACE_EVENT_PERF_PERM(name, expr)
+
#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)


@@ -140,6 +144,9 @@
#undef TRACE_EVENT_FLAGS
#define TRACE_EVENT_FLAGS(event, flag)

+#undef TRACE_EVENT_PERF_PERM
+#define TRACE_EVENT_PERF_PERM(event, expr...)
+
#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)

/*
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 78e27e3..630889f 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -24,6 +24,12 @@ static int total_ref_count;
static int perf_trace_event_perm(struct ftrace_event_call *tp_event,
struct perf_event *p_event)
{
+ if (tp_event->perf_perm) {
+ int ret = tp_event->perf_perm(tp_event, p_event);
+ if (ret)
+ return ret;
+ }
+
/* The ftrace function trace is allowed only for root. */
if (ftrace_event_is_function(tp_event) &&
perf_paranoid_tracepoint_raw() && !capable(CAP_SYS_ADMIN))

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