Commit b89fbfbb authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
Browse files

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: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/bpf/20210815070609.987780-5-andrii@kernel.org
parent 652c1b17

include/linux/bpf_types.h

+3 −0
Original line number Diff line number Diff line
@@ -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

include/linux/trace_events.h

+3 −0
Original line number Diff line number Diff line
@@ -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,

include/uapi/linux/bpf.h

+2 −0
Original line number Diff line number Diff line
@@ -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,

};

kernel/bpf/syscall.c

+98 −7
Original line number Diff line number Diff line
@@ -2906,6 +2906,79 @@ static const struct bpf_link_ops bpf_raw_tp_link_lops = { 
	.fill_link_info = bpf_raw_tp_link_fill_link_info,

};



#ifdef CONFIG_PERF_EVENTS

struct bpf_perf_link {

	struct bpf_link link;

	struct file *perf_file;

};



static void bpf_perf_link_release(struct bpf_link *link)

{

	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);

	struct perf_event *event = perf_link->perf_file->private_data;



	perf_event_free_bpf_prog(event);

	fput(perf_link->perf_file);

}



static void bpf_perf_link_dealloc(struct bpf_link *link)

{

	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);



	kfree(perf_link);

}



static const struct bpf_link_ops bpf_perf_link_lops = {

	.release = bpf_perf_link_release,

	.dealloc = bpf_perf_link_dealloc,

};



static int bpf_perf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)

{

	struct bpf_link_primer link_primer;

	struct bpf_perf_link *link;

	struct perf_event *event;

	struct file *perf_file;

	int err;



	if (attr->link_create.flags)

		return -EINVAL;



	perf_file = perf_event_get(attr->link_create.target_fd);

	if (IS_ERR(perf_file))

		return PTR_ERR(perf_file);



	link = kzalloc(sizeof(*link), GFP_USER);

	if (!link) {

		err = -ENOMEM;

		goto out_put_file;

	}

	bpf_link_init(&link->link, BPF_LINK_TYPE_PERF_EVENT, &bpf_perf_link_lops, prog);

	link->perf_file = perf_file;



	err = bpf_link_prime(&link->link, &link_primer);

	if (err) {

		kfree(link);

		goto out_put_file;

	}



	event = perf_file->private_data;

	err = perf_event_set_bpf_prog(event, prog);

	if (err) {

		bpf_link_cleanup(&link_primer);

		goto out_put_file;

	}

	/* perf_event_set_bpf_prog() doesn't take its own refcnt on prog */

	bpf_prog_inc(prog);



	return bpf_link_settle(&link_primer);



out_put_file:

	fput(perf_file);

	return err;

}

#endif /* CONFIG_PERF_EVENTS */



#define BPF_RAW_TRACEPOINT_OPEN_LAST_FIELD raw_tracepoint.prog_fd



static int bpf_raw_tracepoint_open(const union bpf_attr *attr)
@@ -4147,16 +4220,27 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr) 
	if (ret)

		goto out;



	if (prog->type == BPF_PROG_TYPE_EXT) {

	switch (prog->type) {

	case BPF_PROG_TYPE_EXT:

		ret = tracing_bpf_link_attach(attr, uattr, prog);

		goto out;

	case BPF_PROG_TYPE_PERF_EVENT:

	case BPF_PROG_TYPE_KPROBE:

	case BPF_PROG_TYPE_TRACEPOINT:

		if (attr->link_create.attach_type != BPF_PERF_EVENT) {

			ret = -EINVAL;

			goto out;

		}



		ptype = prog->type;

		break;

	default:

		ptype = attach_type_to_prog_type(attr->link_create.attach_type);

		if (ptype == BPF_PROG_TYPE_UNSPEC || ptype != prog->type) {

			ret = -EINVAL;

			goto out;

		}

		break;

	}



	switch (ptype) {

	case BPF_PROG_TYPE_CGROUP_SKB:
@@ -4179,6 +4263,13 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr) 
	case BPF_PROG_TYPE_XDP:

		ret = bpf_xdp_link_attach(attr, prog);

		break;

#endif

#ifdef CONFIG_PERF_EVENTS

	case BPF_PROG_TYPE_PERF_EVENT:

	case BPF_PROG_TYPE_TRACEPOINT:

	case BPF_PROG_TYPE_KPROBE:

		ret = bpf_perf_link_attach(attr, prog);

		break;

#endif

	default:

		ret = -EINVAL;

kernel/events/core.c

+4 −6
Original line number Diff line number Diff line
@@ -4697,7 +4697,6 @@ find_get_context(struct pmu *pmu, struct task_struct *task, 
}



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 */