bpf: Implement minimal BPF perf link

Introduce a new type of BPF link - BPF perf link. This brings perf_event-based
BPF program attachments (perf_event, tracepoints, kprobes, and uprobes) into
the common BPF link infrastructure, allowing to list all active perf_event
based attachments, auto-detaching BPF program from perf_event when link's FD
is closed, get generic BPF link fdinfo/get_info functionality.

BPF_LINK_CREATE command expects perf_event's FD as target_fd. No extra flags
are currently supported.

Force-detaching and atomic BPF program updates are not yet implemented, but
with perf_event-based BPF links we now have common framework for this without
the need to extend ioctl()-based perf_event interface.

One interesting consideration is a new value for bpf_attach_type, which
BPF_LINK_CREATE command expects. Generally, it's either 1-to-1 mapping from
bpf_attach_type to bpf_prog_type, or many-to-1 mapping from a subset of
bpf_attach_types to one bpf_prog_type (e.g., see BPF_PROG_TYPE_SK_SKB or
BPF_PROG_TYPE_CGROUP_SOCK). In this case, though, we have three different
program types (KPROBE, TRACEPOINT, PERF_EVENT) using the same perf_event-based
mechanism, so it's many bpf_prog_types to one bpf_attach_type. I chose to
define a single BPF_PERF_EVENT attach type for all of them and adjust
link_create()'s logic for checking correspondence between attach type and
program type.

The alternative would be to define three new attach types (e.g., BPF_KPROBE,
BPF_TRACEPOINT, and BPF_PERF_EVENT), but that seemed like unnecessary overkill
and BPF_KPROBE will cause naming conflicts with BPF_KPROBE() macro, defined by
libbpf. I chose to not do this to avoid unnecessary proliferation of
bpf_attach_type enum values and not have to deal with naming conflicts.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/bpf/20210815070609.987780-5-andrii@kernel.org

1 files changed, 4 insertions, 6 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2f07718bd41c..9fd65667bcb2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4697,7 +4697,6 @@ errout:
 }
 
 static void perf_event_free_filter(struct perf_event *event);
-static void perf_event_free_bpf_prog(struct perf_event *event);
 
 static void free_event_rcu(struct rcu_head *head)
 {
@@ -5574,7 +5573,6 @@ static inline int perf_fget_light(int fd, struct fd *p)
 static int perf_event_set_output(struct perf_event *event,
 				 struct perf_event *output_event);
 static int perf_event_set_filter(struct perf_event *event, void __user *arg);
-static int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog);
 static int perf_copy_attr(struct perf_event_attr __user *uattr,
 			  struct perf_event_attr *attr);
 
@@ -10013,7 +10011,7 @@ static inline bool perf_event_is_tracing(struct perf_event *event)
 	return false;
 }
 
-static int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog)
+int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog)
 {
 	bool is_kprobe, is_tracepoint, is_syscall_tp;
 
@@ -10047,7 +10045,7 @@ static int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *pr
 	return perf_event_attach_bpf_prog(event, prog);
 }
 
-static void perf_event_free_bpf_prog(struct perf_event *event)
+void perf_event_free_bpf_prog(struct perf_event *event)
 {
 	if (!perf_event_is_tracing(event)) {
 		perf_event_free_bpf_handler(event);
@@ -10066,12 +10064,12 @@ static void perf_event_free_filter(struct perf_event *event)
 {
 }
 
-static int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog)
+int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog)
 {
 	return -ENOENT;
 }
 
-static void perf_event_free_bpf_prog(struct perf_event *event)
+void perf_event_free_bpf_prog(struct perf_event *event)
 {
 }
 #endif /* CONFIG_EVENT_TRACING */