bpf: add support for sys_enter_* and sys_exit_* tracepoints

Currently, bpf programs cannot be attached to sys_enter_* and sys_exit_*
style tracepoints. The iovisor/bcc issue #748
(https://github.com/iovisor/bcc/issues/748) documents this issue.
For example, if you try to attach a bpf program to tracepoints
syscalls/sys_enter_newfstat, you will get the following error:
   # ./tools/trace.py t:syscalls:sys_enter_newfstat
   Ioctl(PERF_EVENT_IOC_SET_BPF): Invalid argument
   Failed to attach BPF to tracepoint

The main reason is that syscalls/sys_enter_* and syscalls/sys_exit_*
tracepoints are treated differently from other tracepoints and there
is no bpf hook to it.

This patch adds bpf support for these syscalls tracepoints by
  . permitting bpf attachment in ioctl PERF_EVENT_IOC_SET_BPF
  . calling bpf programs in perf_syscall_enter and perf_syscall_exit

The legality of bpf program ctx access is also checked.
Function trace_event_get_offsets returns correct max offset for each
specific syscall tracepoint, which is compared against the maximum offset
access in bpf program.

Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 4 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 426c2ffba16d..a7a6c1d19a49 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8050,7 +8050,7 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
 
 static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 {
-	bool is_kprobe, is_tracepoint;
+	bool is_kprobe, is_tracepoint, is_syscall_tp;
 	struct bpf_prog *prog;
 
 	if (event->attr.type != PERF_TYPE_TRACEPOINT)
@@ -8061,7 +8061,8 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 
 	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)
+	is_syscall_tp = is_syscall_trace_event(event->tp_event);
+	if (!is_kprobe && !is_tracepoint && !is_syscall_tp)
 		/* bpf programs can only be attached to u/kprobe or tracepoint */
 		return -EINVAL;
 
@@ -8070,13 +8071,14 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 		return PTR_ERR(prog);
 
 	if ((is_kprobe && prog->type != BPF_PROG_TYPE_KPROBE) ||
-	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
+	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT) ||
+	    (is_syscall_tp && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
 		/* valid fd, but invalid bpf program type */
 		bpf_prog_put(prog);
 		return -EINVAL;
 	}
 
-	if (is_tracepoint) {
+	if (is_tracepoint || is_syscall_tp) {
 		int off = trace_event_get_offsets(event->tp_event);
 
 		if (prog->aux->max_ctx_offset > off) {