[PATCH net-next v3 0/2] 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.

Changes from v2:
 - Fix a build issue
Changes from v1:
 - Do not use TRACE_EVENT_FL_CAP_ANY to identify syscall tracepoint.
   Instead use trace_event_call->class.

Yonghong Song (2):
  bpf: add support for sys_enter_* and sys_exit_* tracepoints
  bpf: add a test case for syscalls/sys_{enter|exit}_* tracepoints

 include/linux/syscalls.h      | 12 ++++++++
 kernel/events/core.c          |  8 +++--
 kernel/trace/trace_syscalls.c | 53 ++++++++++++++++++++++++++++++--
 samples/bpf/Makefile          |  4 +++
 samples/bpf/syscall_tp_kern.c | 62 +++++++++++++++++++++++++++++++++++++
 samples/bpf/syscall_tp_user.c | 71 +++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 205 insertions(+), 5 deletions(-)
 create mode 100644 samples/bpf/syscall_tp_kern.c
 create mode 100644 samples/bpf/syscall_tp_user.c

-- 
2.9.4

Signed-off-by: Yonghong Song <redacted>
---
 samples/bpf/Makefile          |  4 +++
 samples/bpf/syscall_tp_kern.c | 62 +++++++++++++++++++++++++++++++++++++
 samples/bpf/syscall_tp_user.c | 71 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 137 insertions(+)
 create mode 100644 samples/bpf/syscall_tp_kern.c
 create mode 100644 samples/bpf/syscall_tp_user.c

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 770d46c..f1010fe 100644
--- a/samples/bpf/Makefile
+++ b/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

diff --git a/samples/bpf/syscall_tp_kern.c b/samples/bpf/syscall_tp_kern.c
new file mode 100644
index 0000000..9149c52
--- /dev/null
+++ b/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;
+}

diff --git a/samples/bpf/syscall_tp_user.c b/samples/bpf/syscall_tp_user.c
new file mode 100644
index 0000000..a3cb91e
--- /dev/null
+++ b/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;
+}

-- 
2.9.4

Currently, bpf programs cannot be attached to sys_enter_* and sys_exit_*
style tracepoints. The iovisor/bcc issue #748
(https://github.com/iovisor/bcc/issues/748) documents this issue.
For example, if you try to attach a bpf program to tracepoints
syscalls/sys_enter_newfstat, you will get the following error:
   # ./tools/trace.py t:syscalls:sys_enter_newfstat
   Ioctl(PERF_EVENT_IOC_SET_BPF): Invalid argument
   Failed to attach BPF to tracepoint

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 adds bpf support for these syscalls tracepoints by
  . permitting bpf attachment in ioctl PERF_EVENT_IOC_SET_BPF
  . calling bpf programs in perf_syscall_enter and perf_syscall_exit

Signed-off-by: Yonghong Song <redacted>
---
 include/linux/syscalls.h      | 12 ++++++++++
 kernel/events/core.c          |  8 ++++---
 kernel/trace/trace_syscalls.c | 53 +++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 68 insertions(+), 5 deletions(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 3cb15ea..c917021 100644
--- a/include/linux/syscalls.h
+++ b/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)					\

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 426c2ff..750b8d3 100644
--- a/kernel/events/core.c
+++ b/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;
 

@@ -8070,7 +8071,8 @@ 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;

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 5e10395..3bd9e1c 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/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[6]; /* maximum 6 arguments */
+	} param;
+	int i;
+
+	*(struct pt_regs **)&param = regs;
+	param.syscall_nr = rec->nr;
+	for (i = 0; i < sys_data->nb_args && i < 6; 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);
 }

-- 
2.9.4

On 08/03/2017 06:29 PM, Yonghong Song wrote:

Signed-off-by: Yonghong Song <redacted>

Acked-by: Daniel Borkmann <daniel@iogearbox.net>

On 8/3/17 6:29 AM, Yonghong Song wrote:

hmm. if I read the patch correctly that makes it different from
kprobe/uprobe/tracepoints+bpf behavior. Why make it different and
force user space to perf_event_open() on every cpu?
In other cases it's the job of the bpf program to filter by cpu
if necessary and that is well understood by bcc scripts.

On Thu, Aug 3, 2017 at 7:08 PM, Alexei Starovoitov [off-list ref] wrote:

On 8/3/17 6:29 AM, Yonghong Song wrote:

quoted

@@ -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;
+       }

hmm. if I read the patch correctly that makes it different from
kprobe/uprobe/tracepoints+bpf behavior. Why make it different and
force user space to perf_event_open() on every cpu?
In other cases it's the job of the bpf program to filter by cpu
if necessary and that is well understood by bcc scripts.

The patch actually does allow the bpf program to track all cpus.
The test:

quoted

+       if (!prog && hlist_empty(head))
                return;

ensures that if prog is not empty, it will not return even if the
event in the current cpu is empty. Later on, perf_call_bpf_enter will
be called if prog is not empty. This ensures that
the bpf program will execute regardless of the current cpu.

Maybe I missed anything here?

On 8/3/17 5:09 PM, Y Song wrote:

On Thu, Aug 3, 2017 at 7:08 PM, Alexei Starovoitov [off-list ref] wrote:

quoted

On 8/3/17 6:29 AM, Yonghong Song wrote:

quoted

@@ -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;
+       }

hmm. if I read the patch correctly that makes it different from
kprobe/uprobe/tracepoints+bpf behavior. Why make it different and
force user space to perf_event_open() on every cpu?
In other cases it's the job of the bpf program to filter by cpu
if necessary and that is well understood by bcc scripts.

The patch actually does allow the bpf program to track all cpus.
The test:

quoted

quoted

+       if (!prog && hlist_empty(head))
                return;

ensures that if prog is not empty, it will not return even if the
event in the current cpu is empty. Later on, perf_call_bpf_enter will
be called if prog is not empty. This ensures that
the bpf program will execute regardless of the current cpu.

Maybe I missed anything here?

you're right. sorry. misread && for ||.
That part looks good indeed.

Another question...
that part:
        if (is_tracepoint) {
                int off = trace_event_get_offsets(event->tp_event);

                if (prog->aux->max_ctx_offset > off) {
seems to be not used in this new path...
or new is_syscall_tp is also is_tracepoint ?
If so, then it's ok...
and trace_event_get_offsets() returns the actual number
of syscall args or always upper bound of 6?
just curious how this new code checks that bpf prog cannot
access args[6+].

Thanks!

On 8/4/17 11:40 AM, Alexei Starovoitov wrote:

On 8/3/17 5:09 PM, Y Song wrote:

quoted

On Thu, Aug 3, 2017 at 7:08 PM, Alexei Starovoitov [off-list ref] wrote:

quoted

On 8/3/17 6:29 AM, Yonghong Song wrote:

quoted

@@ -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;
+       }

hmm. if I read the patch correctly that makes it different from
kprobe/uprobe/tracepoints+bpf behavior. Why make it different and
force user space to perf_event_open() on every cpu?
In other cases it's the job of the bpf program to filter by cpu
if necessary and that is well understood by bcc scripts.

The patch actually does allow the bpf program to track all cpus.
The test:

quoted

quoted

+       if (!prog && hlist_empty(head))
                return;

ensures that if prog is not empty, it will not return even if the
event in the current cpu is empty. Later on, perf_call_bpf_enter will
be called if prog is not empty. This ensures that
the bpf program will execute regardless of the current cpu.

Maybe I missed anything here?

you're right. sorry. misread && for ||.
That part looks good indeed.

Another question...
that part:
         if (is_tracepoint) {
                 int off = trace_event_get_offsets(event->tp_event);

                 if (prog->aux->max_ctx_offset > off) {
seems to be not used in this new path...
or new is_syscall_tp is also is_tracepoint ?

Good catch! I think I need "is_tracepoint || is_syscall_tp" here.
If trace_event_get_offsets can get the correct offset for the current
particular syscall_{enter|exit}_* event, we will be find.
I will double check this and have another patch.

If so, then it's ok...
and trace_event_get_offsets() returns the actual number
of syscall args or always upper bound of 6?

Since the specific event is fed here, I think the actual number
will be returned.

just curious how this new code checks that bpf prog cannot
access args[6+].

Thanks!