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Message-ID: <c7952df9-5830-45d3-89bb-b45f2b030e24@gmail.com>
Date: Thu, 25 Jul 2024 14:05:34 +0800
From: Leon Hwang <hffilwlqm@...il.com>
To: Yonghong Song <yonghong.song@...ux.dev>, Zheao Li <me@...jusaka.me>,
Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
John Fastabend <john.fastabend@...il.com>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
<martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
Song Liu <song@...nel.org>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2] bpf: Add bpf_check_attach_target_with_klog
method to output failure logs to kernel
On 25/7/24 13:54, Yonghong Song wrote:
>
> On 7/24/24 10:15 PM, Zheao Li wrote:
>> This is a v2 patch, previous Link:
>> https://lore.kernel.org/bpf/20240724152521.20546-1-me@manjusaka.me/T/#u
>>
>> Compare with v1:
>>
>> 1. Format the code style and signed-off field
>> 2. Use a shorter name bpf_check_attach_target_with_klog instead of
>> original name bpf_check_attach_target_with_kernel_log
>>
>> When attaching a freplace hook, failures can occur,
>> but currently, no output is provided to help developers diagnose the
>> root cause.
>>
>> This commit adds a new method, bpf_check_attach_target_with_klog,
>> which outputs the verifier log to the kernel.
>> Developers can then use dmesg to obtain more detailed information
>> about the failure.
>>
>> For an example of eBPF code,
>> Link:
>> https://github.com/Asphaltt/learn-by-example/blob/main/ebpf/freplace/main.go
>>
>> Co-developed-by: Leon Hwang <hffilwlqm@...il.com>
>> Signed-off-by: Leon Hwang <hffilwlqm@...il.com>
>> Signed-off-by: Zheao Li <me@...jusaka.me>
>> ---
>> include/linux/bpf_verifier.h | 5 +++++
>> kernel/bpf/syscall.c | 5 +++--
>> kernel/bpf/trampoline.c | 6 +++---
>> kernel/bpf/verifier.c | 19 +++++++++++++++++++
>> 4 files changed, 30 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
>> index 5cea15c81b8a..8eddba62c194 100644
>> --- a/include/linux/bpf_verifier.h
>> +++ b/include/linux/bpf_verifier.h
>> @@ -848,6 +848,11 @@ static inline void bpf_trampoline_unpack_key(u64
>> key, u32 *obj_id, u32 *btf_id)
>> *btf_id = key & 0x7FFFFFFF;
>> }
>> +int bpf_check_attach_target_with_klog(const struct bpf_prog *prog,
>> + const struct bpf_prog *tgt_prog,
>> + u32 btf_id,
>> + struct bpf_attach_target_info *tgt_info);
>
> format issue in the above. Same code alignment is needed for arguments
> in different lines.
>
>> +
>> int bpf_check_attach_target(struct bpf_verifier_log *log,
>> const struct bpf_prog *prog,
>> const struct bpf_prog *tgt_prog,
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index 869265852d51..bf826fcc8cf4 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -3464,8 +3464,9 @@ static int bpf_tracing_prog_attach(struct
>> bpf_prog *prog,
>> */
>> struct bpf_attach_target_info tgt_info = {};
>> - err = bpf_check_attach_target(NULL, prog, tgt_prog, btf_id,
>> - &tgt_info);
>> + err = bpf_check_attach_target_with_klog(prog, NULL,
>> + prog->aux->attach_btf_id,
>> + &tgt_info);
>
> code alignment issue here as well.
> Also, the argument should be 'prog, tgt_prog, btf_id, &tgt_info', right?
>
>> if (err)
>> goto out_unlock;
>> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
>> index f8302a5ca400..8862adaa7302 100644
>> --- a/kernel/bpf/trampoline.c
>> +++ b/kernel/bpf/trampoline.c
>> @@ -699,9 +699,9 @@ int bpf_trampoline_link_cgroup_shim(struct
>> bpf_prog *prog,
>> u64 key;
>> int err;
>> - err = bpf_check_attach_target(NULL, prog, NULL,
>> - prog->aux->attach_btf_id,
>> - &tgt_info);
>> + err = bpf_check_attach_target_with_klog(prog, NULL,
>> + prog->aux->attach_btf_id,
>> + &tgt_info);
>
> code alignment issue here
>
>> if (err)
>> return err;
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 1f5302fb0957..4873b72f5a9a 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -21643,6 +21643,25 @@ static int
>> check_non_sleepable_error_inject(u32 btf_id)
>> return btf_id_set_contains(&btf_non_sleepable_error_inject,
>> btf_id);
>> }
>> +int bpf_check_attach_target_with_klog(const struct bpf_prog *prog,
>> + const struct bpf_prog *tgt_prog,
>> + u32 btf_id,
>> + struct bpf_attach_target_info *tgt_info);
>
> code alignment issue here.
>
>> +{
>> + struct bpf_verifier_log *log;
>> + int err;
>> +
>> + log = kzalloc(sizeof(*log), GFP_KERNEL | __GFP_NOWARN);
>
> __GFP_NOWARN is unnecessary here.
>
>> + if (!log) {
>> + err = -ENOMEM;
>> + return err;
>> + }
>> + log->level = BPF_LOG_KERNEL;
>> + err = bpf_check_attach_target(log, prog, tgt_prog, btf_id,
>> tgt_info);
>> + kfree(log);
>> + return err;
>> +}
>> +
>> int bpf_check_attach_target(struct bpf_verifier_log *log,
>> const struct bpf_prog *prog,
>> const struct bpf_prog *tgt_prog,
>
> More importantly, Andrii has implemented retsnoop, which intends to locate
> precise location in the kernel where err happens. The link is
> https://github.com/anakryiko/retsnoop
>
> Maybe you want to take a look and see whether it can resolve your issue.
> We should really avoid putting more stuff in dmesg whenever possible.
>
retsnoop is really cool.
However, when something wrong in bpf_check_attach_target(), retsnoop
only gets its return value -EINVAL, without any bpf_log() in it. It's
hard to figure out the reason why bpf_check_attach_target() returns -EINVAL.
How about adding a tracepoint in bpf_check_attach_target_with_klog()?
It's to avoid putting stuff in dmesg.
Thanks,
Leon
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