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

3 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
index ae3ac3a2018c..9c81724e4b98 100644
--- a/include/linux/bpf_types.h
+++ b/include/linux/bpf_types.h
@@ -136,3 +136,6 @@ BPF_LINK_TYPE(BPF_LINK_TYPE_ITER, iter)
 BPF_LINK_TYPE(BPF_LINK_TYPE_NETNS, netns)
 BPF_LINK_TYPE(BPF_LINK_TYPE_XDP, xdp)
 #endif
+#ifdef CONFIG_PERF_EVENTS
+BPF_LINK_TYPE(BPF_LINK_TYPE_PERF_EVENT, perf)
+#endif
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index ad413b382a3c..8ac92560d3a3 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -803,6 +803,9 @@ extern void ftrace_profile_free_filter(struct perf_event *event);
 void perf_trace_buf_update(void *record, u16 type);
 void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp);
 
+int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog);
+void perf_event_free_bpf_prog(struct perf_event *event);
+
 void bpf_trace_run1(struct bpf_prog *prog, u64 arg1);
 void bpf_trace_run2(struct bpf_prog *prog, u64 arg1, u64 arg2);
 void bpf_trace_run3(struct bpf_prog *prog, u64 arg1, u64 arg2,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2db6925e04f4..94fe8329b28f 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -993,6 +993,7 @@ enum bpf_attach_type {
 	BPF_SK_SKB_VERDICT,
 	BPF_SK_REUSEPORT_SELECT,
 	BPF_SK_REUSEPORT_SELECT_OR_MIGRATE,
+	BPF_PERF_EVENT,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -1006,6 +1007,7 @@ enum bpf_link_type {
 	BPF_LINK_TYPE_ITER = 4,
 	BPF_LINK_TYPE_NETNS = 5,
 	BPF_LINK_TYPE_XDP = 6,
+	BPF_LINK_TYPE_PERF_EVENT = 7,
 
 	MAX_BPF_LINK_TYPE,
 };