Commit cf5f5cea authored by Yonghong Song's avatar Yonghong Song Committed by David S. Miller
Browse files

bpf: add support for sys_enter_* and sys_exit_* tracepoints 

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

The legality of bpf program ctx access is also checked.
Function trace_event_get_offsets returns correct max offset for each
specific syscall tracepoint, which is compared against the maximum offset
access in bpf program.

Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d226a2b8

include/linux/syscalls.h

+12 −0
Original line number Diff line number Diff line
@@ -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

+6 −4
Original line number Diff line number Diff line
@@ -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

+51 −2
Original line number Diff line number Diff line
@@ -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);

}

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