linux-kernel - Re: [PATCH] x86/ibt: make is

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Message-ID: <20250922071911.GQ3245006@noisy.programming.kicks-ass.net>
Date: Mon, 22 Sep 2025 09:19:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: menglong.dong@...ux.dev
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Jiri Olsa <jolsa@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Kees Cook <kees@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Mike Rapoport <rppt@...nel.org>, Andy Lutomirski <luto@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] x86/ibt: make is_endbr() notrace

On Mon, Sep 22, 2025 at 03:13:38PM +0800, menglong.dong@...ux.dev wrote:

> > Anyway, I don't mind making is_endbr() invisible to tracing, that might
> > just have security benefits too. But I think first the ftrace folks need
> > to figure out how to best kill that recursion, because I don't think
> > is_endbr is particularly special here.
> 
> So, does this patch seem useful after all?

The use lies in making it harder to find/manipulate endbr things.

> OK, I'll send a V2 base on your following suggestion.

Hold off until Masami/Steve have fixed the ftrace recursion issue. After
that we can do this.