linux-kernel - Re: [RFC] ftrace: Add support to keep some functions out of ftrace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Yvpf67eCerqaDmlE@worktop.programming.kicks-ass.net>
Date:   Mon, 15 Aug 2022 17:02:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Jiri Olsa <olsajiri@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, bpf <bpf@...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>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [RFC] ftrace: Add support to keep some functions out of ftrace

On Mon, Aug 15, 2022 at 07:45:16AM -0700, Alexei Starovoitov wrote:
> On Mon, Aug 15, 2022 at 7:33 AM Peter Zijlstra <peterz@...radead.org> wrote:

> > It is in full control of the 'call __fentry__'. Absolute full NAK on you
> > trying to make it otherwise.
> 
> Don't mix 'call fentry' generated by the compiler with nop5 inserted
> by macroses or JITs.

Looking at:

 https://lore.kernel.org/all/20191211123017.13212-3-bjorn.topel@gmail.com/

this seems to want to prod at the __fentry__ sites.

> > > Soon we will have nop5 in the middle of the function.
> > > ftrace must not touch it.
> >
> > How are you generating that NOP and what for?
> 
> We're generating nop5-s in JITed code to further
> attach to.

Ftrace doesn't know about those; so how can it break that?

Likewise it doesn't know about the static_branch/static_call NOPs and
nothing is broken.

Ftrace only knows about the __fentry__ sites, and it *does* own them.
Are you saying ftrace is writing to a code location not a __fentry__
site?