From: Hou Tao <houtao1@huawei.com>
To: xufeng zhang <yunbo.xufeng@linux.alibaba.com>, <jolsa@kernel.org>,
<kpsingh@google.com>
Cc: <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<bpf@vger.kernel.org>, <daniel@iogearbox.net>, <ast@kernel.org>,
<andriin@fb.com>
Subject: Re: [RFC] [PATCH bpf-next 1/1] bpf: Clear the noisy tail buffer for bpf_d_path() helper
Date: Wed, 24 Nov 2021 16:49:45 +0800 [thread overview]
Message-ID: <26009981-d1a4-ff37-ca60-f21a43fc7a8c@huawei.com> (raw)
In-Reply-To: <9c83d1c1-f8da-8c5b-74dc-d763ab444774@linux.alibaba.com>
Hi,
On 11/24/2021 12:15 PM, xufeng zhang wrote:
> Jiri and KP,
>
> Any suggestion?
>
>
> Thanks in advance!
>
> Xufeng
>
> 在 2021/11/20 下午1:18, Xufeng Zhang 写道:
>> From: "Xufeng Zhang" <yunbo.xufeng@linux.alibaba.com>
>>
>> The motivation behind this change is to use the returned full path
>> for lookup keys in BPF_MAP_TYPE_HASH map.
>> bpf_d_path() prepend the path string from the end of the input
>> buffer, and call memmove() to copy the full path from the tail
>> buffer to the head of buffer before return. So although the
>> returned buffer string is NULL terminated, there is still
>> noise data at the tail of buffer.
>> If using the returned full path buffer as the key of hash map,
>> the noise data is also calculated and makes map lookup failed.
>> To resolve this problem, we could memset the noisy tail buffer
>> before return.
>>
>> Signed-off-by: Xufeng Zhang <yunbo.xufeng@linux.alibaba.com>
>> ---
>> kernel/trace/bpf_trace.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index 25ea521fb8f1..ec4a6823c024 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -903,6 +903,8 @@ BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf,
>> u32, sz)
>> } else {
>> len = buf + sz - p;
>> memmove(buf, p, len);
>> + /* Clear the noisy tail buffer before return */
>> + memset(buf + len, 0, sz - len);
Is implementing bpf_memset() helper a better idea ? So those who need to
clear the buffer after the terminated null character can use the helper to
do that.
Regards,
Tao
>> }
>> return len;
> .
next prev parent reply other threads:[~2021-11-24 8:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-20 5:18 [RFC] [PATCH bpf-next 0/1] Enhancement for bpf_do_path() helper Xufeng Zhang
2021-11-20 5:18 ` [RFC] [PATCH bpf-next 1/1] bpf: Clear the noisy tail buffer for bpf_d_path() helper Xufeng Zhang
2021-11-24 4:15 ` xufeng zhang
2021-11-24 8:49 ` Hou Tao [this message]
2021-11-25 1:47 ` xufeng zhang
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