linux-kernel - Re: [PATCH 2/2] x86/retpoline,kprobes: Avoid treating rethunk as an indirect jump

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Message-ID: <20230705090244.GH462772@hirez.programming.kicks-ass.net>
Date:   Wed, 5 Jul 2023 11:02:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Petr Pavlu <petr.pavlu@...e.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mhiramat@...nel.org,
        samitolvanen@...gle.com, x86@...nel.org,
        linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/retpoline,kprobes: Avoid treating rethunk as an
 indirect jump

On Wed, Jul 05, 2023 at 10:15:47AM +0200, Petr Pavlu wrote:

> ---
>  arch/x86/kernel/vmlinux.lds.S | 2 --
>  arch/x86/lib/retpoline.S      | 4 ++++
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index a4cd04c458df..dd5b0a68cf84 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -133,9 +133,7 @@ SECTIONS
>  		KPROBES_TEXT
>  		SOFTIRQENTRY_TEXT
>  #ifdef CONFIG_RETPOLINE
> -		__indirect_thunk_start = .;
>  		*(.text..__x86.*)
> -		__indirect_thunk_end = .;
>  #endif

Arguably you could do:

		__indirect_thunk_start = .;
		*(.text..__x86.indirect_thunk)
		__indirect_thunk_end = .;
		*(.text..__x86.return_think)

Or somesuch, seems simpler to me.