linux-kernel - Re: [PATCH v13 bpf-next 0/1] fprobe: Introduce fprobe function entry/exit probe

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Date:   Wed, 23 Mar 2022 14:18:40 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>, catalin.marinas@....com,
        will@...nel.org
Subject: Re: [PATCH v13 bpf-next 0/1] fprobe: Introduce fprobe function
 entry/exit probe

On Wed, Mar 23, 2022 at 11:34:46AM +0900, Masami Hiramatsu wrote:
> Hi,

Hi Masami,

> Here is the 13th version of rethook x86 port. This is developed for a part
> of fprobe series [1] for hooking function return. But since I forgot to send
> it to arch maintainers, that caused conflict with IBT and SLS mitigation series.
> Now I picked the x86 rethook part and send it to x86 maintainers to be
> reviewed.
> 
> [1] https://lore.kernel.org/all/164735281449.1084943.12438881786173547153.stgit@devnote2/T/#u

As mentioned elsewhere, I have similar (though not identical) concerns
to Peter for the arm64 patch, which was equally unreviewed by
maintainers, and the overall structure.

> Note that this patch is still for the bpf-next since the rethook itself
> is on the bpf-next tree. But since this also uses the ANNOTATE_NOENDBR
> macro which has been introduced by IBT/ENDBR patch, to build this series
> you need to merge the tip/master branch with the bpf-next.
> (hopefully, it is rebased soon)

I thought we were going to drop the series from the bpf-next tree so
that this could all go through review it had missed thusfar.

Is that still the plan? What's going on?

> The fprobe itself is for providing the function entry/exit probe
> with multiple probe point. The rethook is a sub-feature to hook the
> function return as same as kretprobe does. Eventually, I would like
> to replace the kretprobe's trampoline with this rethook.

Can we please start by converting each architecture to rethook?

Ideally we'd unify things such that each architecture only needs *one*
return trampoline that both ftrace and krpboes can use, which'd be
significantly easier to get right and manage.

Thanks,
Mark.