netdev - Re: [RFC PATCH bpf-next 1/2] bpf, x64: Fix tailcall infinite loop bug

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Message-ID: <fb6ec982-a0b4-2217-fda3-151cc37ad9a4@gmail.com>
Date: Sat, 19 Aug 2023 11:38:10 +0800
From: Leon Hwang <hffilwlqm@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, X86 ML <x86@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 David Ahern <dsahern@...nel.org>, Yizhou Tang <tangyeechou@...il.com>,
 kernel-patches-bot@...com, "Fijalkowski, Maciej"
 <maciej.fijalkowski@...el.com>, Network Development
 <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [RFC PATCH bpf-next 1/2] bpf, x64: Fix tailcall infinite loop bug

On 2023/8/19 03:59, Alexei Starovoitov wrote:
> On Thu, Aug 17, 2023 at 7:10 PM Leon Hwang <hffilwlqm@...il.com> wrote:
>>
>>
>>
>> On 18/8/23 06:31, Alexei Starovoitov wrote:
>>> On Mon, Aug 14, 2023 at 09:41:46PM +0800, Leon Hwang wrote:
>>>> @@ -1147,6 +1152,7 @@ struct bpf_attach_target_info {
>>>>      struct module *tgt_mod;
>>>>      const char *tgt_name;
>>>>      const struct btf_type *tgt_type;
>>>> +    bool tail_call_ctx;
>>>
>>> Instead of extra flag here can you check tgt_prog->aux->tail_call_reachable in check_attach_btf_id()
>>> and set tr->flags there?
>>
>> Should we check tgt_prog->aux->func[subprog]->is_func? Or, tgt_prog->aux->tail_call_reachable
>> is enough?
> 
> Please let the thread continue to a logical conclusion before resending
> new version. Will reply there.

Sorry for the new version without logical conclusion.

I'll do it better in the future.

Additionally, I'm looking forward to fix it, and then planning to add a
feature to trace tailcalls with trampoline.

Thanks,
Leon