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Date: Thu, 3 Aug 2017 10:08:31 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Yonghong Song <yhs@...com>
Cc: ast@...com, daniel@...earbox.net, netdev@...r.kernel.org,
kernel-team@...com, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH net-next v2 1/2] bpf: add support for sys_enter_* and
sys_exit_* tracepoints
On Wed, Aug 02, 2017 at 10:28:27PM -0700, Yonghong Song wrote:
> 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 <yhs@...com>
Ack for the perf bits, but you should've Cc'ed steve too I suppose.
> ---
> include/linux/syscalls.h | 6 +++++
> kernel/events/core.c | 8 ++++---
> kernel/trace/trace_syscalls.c | 53 +++++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 62 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 3cb15ea..00fa3eb 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -117,6 +117,12 @@ extern struct trace_event_class event_class_syscall_exit;
> extern struct trace_event_functions enter_syscall_print_funcs;
> extern struct trace_event_functions exit_syscall_print_funcs;
>
> +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;
> +}
> +
> #define SYSCALL_TRACE_ENTER_EVENT(sname) \
> static struct syscall_metadata __syscall_meta_##sname; \
> static struct trace_event_call __used \
> 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 **)¶m = 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, ¶m);
> +}
> +
> 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 **)¶m = regs;
> + param.syscall_nr = rec->nr;
> + param.ret = rec->ret;
> + return trace_call_bpf(prog, ¶m);
> +}
> +
> 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
>
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