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Date: Wed, 30 Jun 2021 18:45:46 -0700
From: Yonghong Song <yhs@...com>
To: Masami Hiramatsu <mhiramat@...nel.org>
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>
Subject: Re: [PATCH bpf-next 4/5] bpf: Add bpf_get_func_ip helper for kprobe
programs
On 6/30/21 4:58 PM, Masami Hiramatsu wrote:
> 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)?
How about kretprobe? I guess kp->addr should still point to
function address but instruction_pointer(regs) does not?
>
> 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))
>> [...]
>
>
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