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Message-Id: <20210701085854.0f2aeafc0fce11f3ca9d52a8@kernel.org>
Date: Thu, 1 Jul 2021 08:58:54 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Yonghong Song <yhs@...com>
Cc: Jiri Olsa <jolsa@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andriin@...com>, <netdev@...r.kernel.org>,
<bpf@...r.kernel.org>, Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...omium.org>,
Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH bpf-next 4/5] bpf: Add bpf_get_func_ip helper for kprobe
programs
On Wed, 30 Jun 2021 10:47:01 -0700
Yonghong Song <yhs@...com> wrote:
>
>
> On 6/29/21 12:29 PM, Jiri Olsa wrote:
> > Adding bpf_get_func_ip helper for BPF_PROG_TYPE_KPROBE programs,
> > so it's now possible to call bpf_get_func_ip from both kprobe and
> > kretprobe programs.
> >
> > Taking the caller's address from 'struct kprobe::addr', which is
> > defined for both kprobe and kretprobe.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> > include/uapi/linux/bpf.h | 2 +-
> > kernel/bpf/verifier.c | 2 ++
> > kernel/trace/bpf_trace.c | 14 ++++++++++++++
> > kernel/trace/trace_kprobe.c | 20 ++++++++++++++++++--
> > kernel/trace/trace_probe.h | 5 +++++
> > tools/include/uapi/linux/bpf.h | 2 +-
> > 6 files changed, 41 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 83e87ffdbb6e..4894f99a1993 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -4783,7 +4783,7 @@ union bpf_attr {
> > *
> > * u64 bpf_get_func_ip(void *ctx)
> > * Description
> > - * Get address of the traced function (for tracing programs).
> > + * Get address of the traced function (for tracing and kprobe programs).
> > * Return
> > * Address of the traced function.
> > */
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 701ff7384fa7..b66e0a7104f8 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -5979,6 +5979,8 @@ static bool has_get_func_ip(struct bpf_verifier_env *env)
> > return -ENOTSUPP;
> > }
> > return 0;
> > + } else if (type == BPF_PROG_TYPE_KPROBE) {
> > + return 0;
> > }
> >
> > verbose(env, "func %s#%d not supported for program type %d\n",
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 9edd3b1a00ad..1a5bddce9abd 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -961,6 +961,18 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_tracing = {
> > .arg1_type = ARG_PTR_TO_CTX,
> > };
> >
> > +BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> > +{
> > + return trace_current_kprobe_addr();
> > +}
> > +
> > +static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
> > + .func = bpf_get_func_ip_kprobe,
> > + .gpl_only = true,
> > + .ret_type = RET_INTEGER,
> > + .arg1_type = ARG_PTR_TO_CTX,
> > +};
> > +
> > const struct bpf_func_proto *
> > bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> > {
> > @@ -1092,6 +1104,8 @@ kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> > case BPF_FUNC_override_return:
> > return &bpf_override_return_proto;
> > #endif
> > + case BPF_FUNC_get_func_ip:
> > + return &bpf_get_func_ip_proto_kprobe;
> > default:
> > return bpf_tracing_func_proto(func_id, prog);
> > }
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index ea6178cb5e33..b07d5888db14 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1570,6 +1570,18 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
> > }
> >
> > #ifdef CONFIG_PERF_EVENTS
> > +/* Used by bpf get_func_ip helper */
> > +DEFINE_PER_CPU(u64, current_kprobe_addr) = 0;
>
> Didn't check other architectures. But this should work
> for x86 where if nested kprobe happens, the second
> kprobe will not call kprobe handlers.
No problem, other architecture also does not call nested kprobes handlers.
However, you don't need this because you can use kprobe_running()
in kprobe context.
kp = kprobe_running();
if (kp)
return kp->addr;
BTW, I'm not sure why don't you use instruction_pointer(regs)?
Thank you,
>
> This essentially is to provide an additional parameter to
> bpf program. Andrii is developing a mechanism to
> save arbitrary data in *current task_struct*, which
> might be used here to save current_kprobe_addr, we can
> save one per cpu variable.
>
> > +
> > +u64 trace_current_kprobe_addr(void)
> > +{
> > + return *this_cpu_ptr(¤t_kprobe_addr);
> > +}
> > +
> > +static void trace_current_kprobe_set(struct trace_kprobe *tk)
> > +{
> > + __this_cpu_write(current_kprobe_addr, (u64) tk->rp.kp.addr);
> > +}
> >
> > /* Kprobe profile handler */
> > static int
> > @@ -1585,6 +1597,7 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
> > unsigned long orig_ip = instruction_pointer(regs);
> > int ret;
> >
> > + trace_current_kprobe_set(tk);
> > ret = trace_call_bpf(call, regs);
> >
> > /*
> > @@ -1631,8 +1644,11 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
> > int size, __size, dsize;
> > int rctx;
> >
> > - if (bpf_prog_array_valid(call) && !trace_call_bpf(call, regs))
> > - return;
> > + if (bpf_prog_array_valid(call)) {
> > + trace_current_kprobe_set(tk);
> > + if (!trace_call_bpf(call, regs))
> > + return;
> > + }
> >
> > head = this_cpu_ptr(call->perf_events);
> > if (hlist_empty(head))
> [...]
--
Masami Hiramatsu <mhiramat@...nel.org>
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