Merge branch 'bpf-add-support-for-sys-enter-exit-tracepoints'

Yonghong Song says:

====================
bpf: add support for sys_{enter|exit}_* tracepoints

Currently, bpf programs cannot be attached to sys_enter_* and sys_exit_*
style tracepoints. The main reason is that syscalls/sys_enter_* and syscalls/sys_exit_*
tracepoints are treated differently from other tracepoints and there
is no bpf hook to it.

This patch set adds bpf support for these syscalls tracepoints and also
adds a test case for it.

Changelogs:
v3 -> v4:
 - Check the legality of ctx offset access for syscall tracepoint as well.
   trace_event_get_offsets will return correct max offset for each
   specific syscall tracepoint.
 - Use variable length array to avoid hardcode 6 as the maximum
   arguments beyond syscall_nr.
v2 -> v3:
 - Fix a build issue
v1 -> v2:
 - Do not use TRACE_EVENT_FL_CAP_ANY to identify syscall tracepoint.
   Instead use trace_event_call->class.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/syscalls.h

@@ -172,8 +172,20 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 	static struct syscall_metadata __used			\
 	  __attribute__((section("__syscalls_metadata")))	\
 	 *__p_syscall_meta_##sname = &__syscall_meta_##sname;
+
+static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
+{
+	return tp_event->class == &event_class_syscall_enter ||
+	       tp_event->class == &event_class_syscall_exit;
+}
+
 #else
 #define SYSCALL_METADATA(sname, nb, ...)
+
+static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
+{
+	return 0;
+}
 #endif
 
 #define SYSCALL_DEFINE0(sname)					\

kernel/events/core.c

@@ -8050,7 +8050,7 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
 
 static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 {
-	bool is_kprobe, is_tracepoint;
+	bool is_kprobe, is_tracepoint, is_syscall_tp;
 	struct bpf_prog *prog;
 
 	if (event->attr.type != PERF_TYPE_TRACEPOINT)
@@ -8061,7 +8061,8 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 
 	is_kprobe = event->tp_event->flags & TRACE_EVENT_FL_UKPROBE;
 	is_tracepoint = event->tp_event->flags & TRACE_EVENT_FL_TRACEPOINT;
-	if (!is_kprobe && !is_tracepoint)
+	is_syscall_tp = is_syscall_trace_event(event->tp_event);
+	if (!is_kprobe && !is_tracepoint && !is_syscall_tp)
 		/* bpf programs can only be attached to u/kprobe or tracepoint */
 		return -EINVAL;
 
@@ -8070,13 +8071,14 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 		return PTR_ERR(prog);
 
 	if ((is_kprobe && prog->type != BPF_PROG_TYPE_KPROBE) ||
-	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
+	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT) ||
+	    (is_syscall_tp && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
 		/* valid fd, but invalid bpf program type */
 		bpf_prog_put(prog);
 		return -EINVAL;
 	}
 
-	if (is_tracepoint) {
+	if (is_tracepoint || is_syscall_tp) {
 		int off = trace_event_get_offsets(event->tp_event);
 
 		if (prog->aux->max_ctx_offset > off) {

kernel/trace/trace_syscalls.c

@@ -559,11 +559,29 @@ static DECLARE_BITMAP(enabled_perf_exit_syscalls, NR_syscalls);
 static int sys_perf_refcount_enter;
 static int sys_perf_refcount_exit;
 
+static int perf_call_bpf_enter(struct bpf_prog *prog, struct pt_regs *regs,
+			      struct syscall_metadata *sys_data,
+			      struct syscall_trace_enter *rec) {
+	struct syscall_tp_t {
+		unsigned long long regs;
+		unsigned long syscall_nr;
+		unsigned long args[sys_data->nb_args];
+	} param;
+	int i;
+
+	*(struct pt_regs **)&param = regs;
+	param.syscall_nr = rec->nr;
+	for (i = 0; i < sys_data->nb_args; i++)
+		param.args[i] = rec->args[i];
+	return trace_call_bpf(prog, &param);
+}
+
 static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 {
 	struct syscall_metadata *sys_data;
 	struct syscall_trace_enter *rec;
 	struct hlist_head *head;
+	struct bpf_prog *prog;
 	int syscall_nr;
 	int rctx;
 	int size;
@@ -578,8 +596,9 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	if (!sys_data)
 		return;
 
+	prog = READ_ONCE(sys_data->enter_event->prog);
 	head = this_cpu_ptr(sys_data->enter_event->perf_events);
-	if (hlist_empty(head))
+	if (!prog && hlist_empty(head))
 		return;
 
 	/* get the size after alignment with the u32 buffer size field */
@@ -594,6 +613,13 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	rec->nr = syscall_nr;
 	syscall_get_arguments(current, regs, 0, sys_data->nb_args,
 			       (unsigned long *)&rec->args);
+
+	if ((prog && !perf_call_bpf_enter(prog, regs, sys_data, rec)) ||
+	    hlist_empty(head)) {
+		perf_swevent_put_recursion_context(rctx);
+		return;
+	}
+
 	perf_trace_buf_submit(rec, size, rctx,
 			      sys_data->enter_event->event.type, 1, regs,
 			      head, NULL);
@@ -633,11 +659,26 @@ static void perf_sysenter_disable(struct trace_event_call *call)
 	mutex_unlock(&syscall_trace_lock);
 }
 
+static int perf_call_bpf_exit(struct bpf_prog *prog, struct pt_regs *regs,
+			      struct syscall_trace_exit *rec) {
+	struct syscall_tp_t {
+		unsigned long long regs;
+		unsigned long syscall_nr;
+		unsigned long ret;
+	} param;
+
+	*(struct pt_regs **)&param = regs;
+	param.syscall_nr = rec->nr;
+	param.ret = rec->ret;
+	return trace_call_bpf(prog, &param);
+}
+
 static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 {
 	struct syscall_metadata *sys_data;
 	struct syscall_trace_exit *rec;
 	struct hlist_head *head;
+	struct bpf_prog *prog;
 	int syscall_nr;
 	int rctx;
 	int size;
@@ -652,8 +693,9 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	if (!sys_data)
 		return;
 
+	prog = READ_ONCE(sys_data->exit_event->prog);
 	head = this_cpu_ptr(sys_data->exit_event->perf_events);
-	if (hlist_empty(head))
+	if (!prog && hlist_empty(head))
 		return;
 
 	/* We can probably do that at build time */
@@ -666,6 +708,13 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 
 	rec->nr = syscall_nr;
 	rec->ret = syscall_get_return_value(current, regs);
+
+	if ((prog && !perf_call_bpf_exit(prog, regs, rec)) ||
+	    hlist_empty(head)) {
+		perf_swevent_put_recursion_context(rctx);
+		return;
+	}
+
 	perf_trace_buf_submit(rec, size, rctx, sys_data->exit_event->event.type,
 			      1, regs, head, NULL);
 }

samples/bpf/Makefile

@@ -39,6 +39,7 @@ hostprogs-y += per_socket_stats_example
 hostprogs-y += load_sock_ops
 hostprogs-y += xdp_redirect
 hostprogs-y += xdp_redirect_map
+hostprogs-y += syscall_tp
 
 # Libbpf dependencies
 LIBBPF := ../../tools/lib/bpf/bpf.o
@@ -82,6 +83,7 @@ test_map_in_map-objs := bpf_load.o $(LIBBPF) test_map_in_map_user.o
 per_socket_stats_example-objs := $(LIBBPF) cookie_uid_helper_example.o
 xdp_redirect-objs := bpf_load.o $(LIBBPF) xdp_redirect_user.o
 xdp_redirect_map-objs := bpf_load.o $(LIBBPF) xdp_redirect_map_user.o
+syscall_tp-objs := bpf_load.o $(LIBBPF) syscall_tp_user.o
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
@@ -125,6 +127,7 @@ always += tcp_iw_kern.o
 always += tcp_clamp_kern.o
 always += xdp_redirect_kern.o
 always += xdp_redirect_map_kern.o
+always += syscall_tp_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
@@ -163,6 +166,7 @@ HOSTLOADLIBES_xdp_tx_iptunnel += -lelf
 HOSTLOADLIBES_test_map_in_map += -lelf
 HOSTLOADLIBES_xdp_redirect += -lelf
 HOSTLOADLIBES_xdp_redirect_map += -lelf
+HOSTLOADLIBES_syscall_tp += -lelf
 
 # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
 #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang

samples/bpf/syscall_tp_kern.c

@@ -0,0 +1,62 @@
+/* Copyright (c) 2017 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <uapi/linux/bpf.h>
+#include "bpf_helpers.h"
+
+struct syscalls_enter_open_args {
+	unsigned long long unused;
+	long syscall_nr;
+	long filename_ptr;
+	long flags;
+	long mode;
+};
+
+struct syscalls_exit_open_args {
+	unsigned long long unused;
+	long syscall_nr;
+	long ret;
+};
+
+struct bpf_map_def SEC("maps") enter_open_map = {
+	.type = BPF_MAP_TYPE_ARRAY,
+	.key_size = sizeof(u32),
+	.value_size = sizeof(u32),
+	.max_entries = 1,
+};
+
+struct bpf_map_def SEC("maps") exit_open_map = {
+	.type = BPF_MAP_TYPE_ARRAY,
+	.key_size = sizeof(u32),
+	.value_size = sizeof(u32),
+	.max_entries = 1,
+};
+
+static __always_inline void count(void *map)
+{
+	u32 key = 0;
+	u32 *value, init_val = 1;
+
+	value = bpf_map_lookup_elem(map, &key);
+	if (value)
+		*value += 1;
+	else
+		bpf_map_update_elem(map, &key, &init_val, BPF_NOEXIST);
+}
+
+SEC("tracepoint/syscalls/sys_enter_open")
+int trace_enter_open(struct syscalls_enter_open_args *ctx)
+{
+	count((void *)&enter_open_map);
+	return 0;
+}
+
+SEC("tracepoint/syscalls/sys_exit_open")
+int trace_enter_exit(struct syscalls_exit_open_args *ctx)
+{
+	count((void *)&exit_open_map);
+	return 0;
+}

samples/bpf/syscall_tp_user.c

@@ -0,0 +1,71 @@
+/* Copyright (c) 2017 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <linux/bpf.h>
+#include <string.h>
+#include <linux/perf_event.h>
+#include <errno.h>
+#include <assert.h>
+#include <stdbool.h>
+#include <sys/resource.h>
+#include "libbpf.h"
+#include "bpf_load.h"
+
+/* This program verifies bpf attachment to tracepoint sys_enter_* and sys_exit_*.
+ * This requires kernel CONFIG_FTRACE_SYSCALLS to be set.
+ */
+
+static void verify_map(int map_id)
+{
+	__u32 key = 0;
+	__u32 val;
+
+	if (bpf_map_lookup_elem(map_id, &key, &val) != 0) {
+		fprintf(stderr, "map_lookup failed: %s\n", strerror(errno));
+		return;
+	}
+	if (val == 0)
+		fprintf(stderr, "failed: map #%d returns value 0\n", map_id);
+}
+
+int main(int argc, char **argv)
+{
+	struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
+	char filename[256];
+	int fd;
+
+	setrlimit(RLIMIT_MEMLOCK, &r);
+	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+	if (load_bpf_file(filename)) {
+		fprintf(stderr, "%s", bpf_log_buf);
+		return 1;
+	}
+
+	/* current load_bpf_file has perf_event_open default pid = -1
+	 * and cpu = 0, which permits attached bpf execution on
+	 * all cpus for all pid's. bpf program execution ignores
+	 * cpu affinity.
+	 */
+	/* trigger some "open" operations */
+	fd = open(filename, O_RDONLY);
+	if (fd < 0) {
+		fprintf(stderr, "open failed: %s\n", strerror(errno));
+		return 1;
+	}
+	close(fd);
+
+	/* verify the map */
+	verify_map(map_fd[0]);
+	verify_map(map_fd[1]);
+
+	return 0;
+}