linux-kernel - Re: nop5-optimized USDTs WAS: Re: [PATCHv6 perf/core 09/22] uprobes/x86: Add uprobe syscall to speed up uprobe

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: <CAEf4BzY216jgetzA_TBY7_jSkcw-TGCj64s96ijoi3iAhcyHuw@mail.gmail.com>
Date: Thu, 4 Sep 2025 14:44:03 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Olsa <olsajiri@...il.com>, Oleg Nesterov <oleg@...hat.com>, 
	Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>, 
	open list <linux-kernel@...r.kernel.org>, 
	Linux trace kernel <linux-trace-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>, 
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, Hao Luo <haoluo@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Alan Maguire <alan.maguire@...cle.com>, David Laight <David.Laight@...lab.com>, 
	Thomas Weißschuh <thomas@...ch.de>, 
	Ingo Molnar <mingo@...nel.org>
Subject: Re: nop5-optimized USDTs WAS: Re: [PATCHv6 perf/core 09/22]
 uprobes/x86: Add uprobe syscall to speed up uprobe

On Thu, Sep 4, 2025 at 1:52 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Sep 04, 2025 at 01:49:49PM -0700, Andrii Nakryiko wrote:
> > On Thu, Sep 4, 2025 at 1:35 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > On Thu, Sep 04, 2025 at 11:27:45AM -0700, Andrii Nakryiko wrote:
> > >
> > > > > > So I've been thinking what's the simplest and most reliable way to
> > > > > > feature-detect support for this sys_uprobe (e.g., for libbpf to know
> > > > > > whether we should attach at nop5 vs nop1), and clearly that would be
> > > > >
> > > > > wrt nop5/nop1.. so the idea is to have USDT macro emit both nop1,nop5
> > > > > and store some info about that in the usdt's elf note, right?
> > >
> > > Wait, what? You're doing to emit 6 bytes and two nops? Why? Surely the
> > > old kernel can INT3 on top of a NOP5?
> > >
> >
> > Yes it can, but it's 2x slower in terms of uprobe triggering compared
> > to nop1.
>
> Why? That doesn't really make sense.
>

Of course it's silly... It's because nop5 wasn't recognized as one of
the emulated instructions, so was handled through single-stepping.

> I realize its probably to late to fix the old kernel not to be stupid --
> this must be something stupid, right? But now I need to know.

Jiri fixed this, but as you said, too late for old kernels. See [0]
for the patch that landed not so long ago.

  [0] https://lore.kernel.org/all/20250414083647.1234007-1-jolsa@kernel.org/