perf, bpf: allow bpf programs attach to tracepoints

introduce BPF_PROG_TYPE_TRACEPOINT program type and allow it to be attached
to the perf tracepoint handler, which will copy the arguments into
the per-cpu buffer and pass it to the bpf program as its first argument.
The layout of the fields can be discovered by doing
'cat /sys/kernel/debug/tracing/events/sched/sched_switch/format'
prior to the compilation of the program with exception that first 8 bytes
are reserved and not accessible to the program. This area is used to store
the pointer to 'struct pt_regs' which some of the bpf helpers will use:
+---------+
| 8 bytes | hidden 'struct pt_regs *' (inaccessible to bpf program)
+---------+
| N bytes | static tracepoint fields defined in tracepoint/format (bpf readonly)
+---------+
| dynamic | __dynamic_array bytes of tracepoint (inaccessible to bpf yet)
+---------+

Not that all of the fields are already dumped to user space via perf ring buffer
and broken application access it directly without consulting tracepoint/format.
Same rule applies here: static tracepoint fields should only be accessed
in a format defined in tracepoint/format. The order of fields and
field sizes are not an ABI.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 4 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d851288..e5ffe97 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6725,12 +6725,13 @@ int perf_swevent_get_recursion_context(void)
 }
 EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);
 
-inline void perf_swevent_put_recursion_context(int rctx)
+void perf_swevent_put_recursion_context(int rctx)
 {
 	struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
 
 	put_recursion_context(swhash->recursion, rctx);
 }
+EXPORT_SYMBOL_GPL(perf_swevent_put_recursion_context);
 
 void ___perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
 {
@@ -7106,6 +7107,7 @@ static void perf_event_free_filter(struct perf_event *event)
 
 static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 {
+	bool is_kprobe, is_tracepoint;
 	struct bpf_prog *prog;
 
 	if (event->attr.type != PERF_TYPE_TRACEPOINT)
@@ -7114,15 +7116,18 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 	if (event->tp_event->prog)
 		return -EEXIST;
 
-	if (!(event->tp_event->flags & TRACE_EVENT_FL_UKPROBE))
-		/* bpf programs can only be attached to u/kprobes */
+	is_kprobe = event->tp_event->flags & TRACE_EVENT_FL_UKPROBE;
+	is_tracepoint = event->tp_event->flags & TRACE_EVENT_FL_TRACEPOINT;
+	if (!is_kprobe && !is_tracepoint)
+		/* bpf programs can only be attached to u/kprobe or tracepoint */
 		return -EINVAL;
 
 	prog = bpf_prog_get(prog_fd);
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
 
-	if (prog->type != BPF_PROG_TYPE_KPROBE) {
+	if ((is_kprobe && prog->type != BPF_PROG_TYPE_KPROBE) ||
+	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
 		/* valid fd, but invalid bpf program type */
 		bpf_prog_put(prog);
 		return -EINVAL;