linux-kernel - Re: [PATCH v5 1/2] kprobes: textmem API

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Date: Tue, 26 Mar 2024 02:36:10 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Masami Hiramatsu" <mhiramat@...nel.org>
Cc: <linux-riscv@...ts.infradead.org>, "Paul Walmsley"
 <paul.walmsley@...ive.com>, "Palmer Dabbelt" <palmer@...belt.com>, "Albert
 Ou" <aou@...s.berkeley.edu>, <linux-kernel@...r.kernel.org>, "Luis
 Chamberlain" <mcgrof@...nel.org>, <linux-modules@...r.kernel.org>, "Naveen
 N . Rao" <naveen.n.rao@...ux.ibm.com>, "Anil S Keshavamurthy"
 <anil.s.keshavamurthy@...el.com>, "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH v5 1/2] kprobes: textmem API

On Tue Mar 26, 2024 at 1:50 AM EET, Masami Hiramatsu (Google) wrote:
> On Tue, 26 Mar 2024 00:09:42 +0200
> "Jarkko Sakkinen" <jarkko@...nel.org> wrote:
>
> > On Mon Mar 25, 2024 at 11:55 PM EET, Jarkko Sakkinen wrote:
> > > +#ifdef CONFIG_MODULES
> > >  	if (register_module_notifier(&trace_kprobe_module_nb))
> > >  		return -EINVAL;
> > > +#endif /* CONFIG_MODULES */
> > 
> > register_module_notifier() does have "dummy" version but what
> > would I pass to it. It makes more mess than it cleans to declare
> > also a "dummy" version of trace_kprobe_module_nb.
>
> That is better than having #ifdef in the function.
>
> > 
> > The callback itself has too tight module subsystem bindings so
> > that they could be simply flagged with IS_DEFINED() (or correct
> > if I'm mistaken, this the conclusion I've ended up with).
>
> Please try this.
>
> -----
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 70dc6179086e..bc98db14927f 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2625,6 +2625,7 @@ static void remove_module_kprobe_blacklist(struct module *mod)
>  	}
>  }
>  
> +#ifdef CONFIG_MODULES
>  /* Module notifier call back, checking kprobes on the module */
>  static int kprobes_module_callback(struct notifier_block *nb,
>  				   unsigned long val, void *data)
> @@ -2675,6 +2676,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
>  	mutex_unlock(&kprobe_mutex);
>  	return NOTIFY_DONE;
>  }
> +#else
> +#define kprobes_module_callback	(NULL)
> +#endif
>  
>  static struct notifier_block kprobe_module_nb = {
>  	.notifier_call = kprobes_module_callback,
> @@ -2739,7 +2743,7 @@ static int __init init_kprobes(void)
>  	err = arch_init_kprobes();
>  	if (!err)
>  		err = register_die_notifier(&kprobe_exceptions_nb);
> -	if (!err)
> +	if (!err && IS_ENABLED(CONFIG_MODULES))
>  		err = register_module_notifier(&kprobe_module_nb);
>  
>  	kprobes_initialized = (err == 0);

OK, thanks for the suggestion WFM.

I'll give this also a spin with VisionFive2 RISC-V SBC before sending
v6.

BR, Jarkko