[PATCH net-next v2 1/2] bpf/tracing: allow user space to query prog array on the same tp

STALE3241d SUPERSEDED: 1 (1M)

From: Yonghong Song <hidden>
Date: 2017-12-06 06:31:32
Subsystem: bpf [core], bpf [general] (safe dynamic programs and tools), bpf [security & lsm] (security audit and enforcement using bpf), bpf [tracing], performance events subsystem, the rest, tracing · Maintainers: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, KP Singh, Matt Bobrowski, Song Liu, Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds, Steven Rostedt, Masami Hiramatsu

Revision v2 of 4 in this series; 1 review trailer (1 from subsystem maintainers).

Revisions (4)

2017-11-29 v1 [diff vs current]
2017-12-06 v2 current
2017-12-06 v3 [diff vs current]
2017-12-11 v4 [diff vs current]

Commit e87c6bc3852b ("bpf: permit multiple bpf attachments
for a single perf event") added support to attach multiple
bpf programs to a single perf event.
Commit 2541517c32be ("tracing, perf: Implement BPF programs
attached to kprobes") utilized the existing perf ioctl
interface and added the command PERF_EVENT_IOC_SET_BPF
to attach a bpf program to a tracepoint.

This patch adds a new ioctl
command, given a perf event fd, to query the bpf program array
attached to the same perf tracepoint event.

The new uapi ioctl command:
  PERF_EVENT_IOC_QUERY_BPF

The new uapi/linux/perf_event.h structure:
  struct perf_event_query_bpf {
       __u64	prog_ids;
       __u32	prog_cnt;
  };

The usage:
  struct perf_event_query_bpf query;
  query.prog_ids = (__u64)usr_prog_ids_buf;
  query.prog_cnt = usr_prog_ids_buf_len;
  err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, &query);

Signed-off-by: Yonghong Song <redacted>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/bpf.h             |  4 ++++
 include/uapi/linux/perf_event.h |  6 ++++++
 kernel/bpf/core.c               | 21 +++++++++++++++++++++
 kernel/events/core.c            |  3 +++
 kernel/trace/bpf_trace.c        | 23 +++++++++++++++++++++++
 5 files changed, 57 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e55e425..f812ac5 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -254,6 +254,7 @@ typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,
 
 u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
 		     void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy);
+int bpf_event_query_prog_array(struct perf_event *event, void __user *info);
 
 int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 			  union bpf_attr __user *uattr);

@@ -285,6 +286,9 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
 
 void bpf_prog_array_delete_safe(struct bpf_prog_array __rcu *progs,
 				struct bpf_prog *old_prog);
+int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
+			     __u32 __user *prog_ids, u32 request_cnt,
+			     __u32 __user *prog_cnt);
 int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
 			struct bpf_prog *exclude_prog,
 			struct bpf_prog *include_prog,

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index b9a4953..fee0b43 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h

@@ -418,6 +418,11 @@ struct perf_event_attr {
 	__u16	__reserved_2;	/* align to __u64 */
 };
 
+struct perf_event_query_bpf {
+	__u64	prog_ids;
+	__u32	prog_cnt;
+};
+
 #define perf_flags(attr)	(*(&(attr)->read_format + 1))
 
 /*

@@ -433,6 +438,7 @@ struct perf_event_attr {
 #define PERF_EVENT_IOC_ID		_IOR('$', 7, __u64 *)
 #define PERF_EVENT_IOC_SET_BPF		_IOW('$', 8, __u32)
 #define PERF_EVENT_IOC_PAUSE_OUTPUT	_IOW('$', 9, __u32)
+#define PERF_EVENT_IOC_QUERY_BPF	_IOWR('$', 10, struct perf_event_query_bpf *)
 
 enum perf_event_ioc_flags {
 	PERF_IOC_FLAG_GROUP		= 1U << 0,

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 86b50aa..35b427aa 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c

@@ -1462,6 +1462,8 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
 	rcu_read_lock();
 	prog = rcu_dereference(progs)->progs;
 	for (; *prog; prog++) {
+		if (*prog == &dummy_bpf_prog.prog)
+			continue;
 		id = (*prog)->aux->id;
 		if (copy_to_user(prog_ids + i, &id, sizeof(id))) {
 			rcu_read_unlock();

@@ -1545,6 +1547,25 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
 	return 0;
 }
 
+int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
+			     __u32 __user *prog_ids, u32 request_cnt,
+			     __u32 __user *prog_cnt)
+{
+	u32 cnt = 0;
+
+	if (array)
+		cnt = bpf_prog_array_length(array);
+
+	if (copy_to_user(prog_cnt, &cnt, sizeof(cnt)))
+		return -EFAULT;
+
+	/* return early if user requested only program count or nothing to copy */
+	if (!request_cnt || !prog_ids || !cnt)
+		return 0;
+
+	return bpf_prog_array_copy_to_user(array, prog_ids, request_cnt);
+}
+
 static void bpf_prog_free_deferred(struct work_struct *work)
 {
 	struct bpf_prog_aux *aux;

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 16beab4..f10609e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c

@@ -4723,6 +4723,9 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
 		rcu_read_unlock();
 		return 0;
 	}
+
+	case PERF_EVENT_IOC_QUERY_BPF:
+		return bpf_event_query_prog_array(event, (void __user *)arg);
 	default:
 		return -ENOTTY;
 	}

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0ce99c3..81eedb2 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c

@@ -820,3 +820,26 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
 unlock:
 	mutex_unlock(&bpf_event_mutex);
 }
+
+int bpf_event_query_prog_array(struct perf_event *event, void __user *info)
+{
+	struct perf_event_query_bpf __user *uquery = info;
+	struct perf_event_query_bpf query = {};
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	if (event->attr.type != PERF_TYPE_TRACEPOINT)
+		return -EINVAL;
+	if (copy_from_user(&query, uquery, sizeof(query)))
+		return -EFAULT;
+
+	mutex_lock(&bpf_event_mutex);
+	ret = bpf_prog_array_copy_info(event->tp_event->prog_array,
+				       u64_to_user_ptr(query.prog_ids),
+				       query.prog_cnt,
+				       &uquery->prog_cnt);
+	mutex_unlock(&bpf_event_mutex);
+
+	return ret;
+}

-- 
2.9.5

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