tracing, perf: Implement BPF programs attached to kprobes

BPF programs, attached to kprobes, provide a safe way to execute
user-defined BPF byte-code programs without being able to crash or
hang the kernel in any way. The BPF engine makes sure that such
programs have a finite execution time and that they cannot break
out of their sandbox.

The user interface is to attach to a kprobe via the perf syscall:

	struct perf_event_attr attr = {
		.type	= PERF_TYPE_TRACEPOINT,
		.config	= event_id,
		...
	};

	event_fd = perf_event_open(&attr,...);
	ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);

'prog_fd' is a file descriptor associated with BPF program
previously loaded.

'event_id' is an ID of the kprobe created.

Closing 'event_fd':

	close(event_fd);

... automatically detaches BPF program from it.

BPF programs can call in-kernel helper functions to:

  - lookup/update/delete elements in maps

  - probe_read - wraper of probe_kernel_read() used to access any
    kernel data structures

BPF programs receive 'struct pt_regs *' as an input ('struct pt_regs' is
architecture dependent) and return 0 to ignore the event and 1 to store
kprobe event into the ring buffer.

Note, kprobes are a fundamentally _not_ a stable kernel ABI,
so BPF programs attached to kprobes must be recompiled for
every kernel version and user must supply correct LINUX_VERSION_CODE
in attr.kern_version during bpf_prog_load() call.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1427312966-8434-4-git-send-email-ast@plumgrid.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 77325e1..0aa535b 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -13,6 +13,7 @@ struct trace_array;
 struct trace_buffer;
 struct tracer;
 struct dentry;
+struct bpf_prog;
 
 struct trace_print_flags {
 	unsigned long		mask;
@@ -306,6 +307,7 @@ struct ftrace_event_call {
 #ifdef CONFIG_PERF_EVENTS
 	int				perf_refcount;
 	struct hlist_head __percpu	*perf_events;
+	struct bpf_prog			*prog;
 
 	int	(*perf_perm)(struct ftrace_event_call *,
 			     struct perf_event *);
@@ -551,6 +553,15 @@ event_trigger_unlock_commit_regs(struct ftrace_event_file *file,
 		event_triggers_post_call(file, tt);
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx);
+#else
+static inline unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
+{
+	return 1;
+}
+#endif
+
 enum {
 	FILTER_OTHER = 0,
 	FILTER_STATIC_STRING,