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: <20250904205210.GQ3245006@noisy.programming.kicks-ass.net>
Date: Thu, 4 Sep 2025 22:52:10 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
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 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.

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.