linux-kernel - Re: [PATCH v4 14/15] kprobes: remove dependency on CONFIG

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Message-ID: <ZiOea81saMutayxt@kernel.org>
Date: Sat, 20 Apr 2024 13:52:27 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
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Subject: Re: [PATCH v4 14/15] kprobes: remove dependency on CONFIG_MODULES

On Sat, Apr 20, 2024 at 06:15:00PM +0900, Masami Hiramatsu wrote:
> On Sat, 20 Apr 2024 10:33:38 +0300
> Mike Rapoport <rppt@...nel.org> wrote:
> 
> > On Fri, Apr 19, 2024 at 03:59:40PM +0000, Christophe Leroy wrote:
> > > 
> > > 
> > > Le 19/04/2024 à 17:49, Mike Rapoport a écrit :
> > > > Hi Masami,
> > > > 
> > > > On Thu, Apr 18, 2024 at 06:16:15AM +0900, Masami Hiramatsu wrote:
> > > >> Hi Mike,
> > > >>
> > > >> On Thu, 11 Apr 2024 19:00:50 +0300
> > > >> Mike Rapoport <rppt@...nel.org> wrote:
> > > >>
> > > >>> From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> > > >>>
> > > >>> kprobes depended on CONFIG_MODULES because it has to allocate memory for
> > > >>> code.
> > > >>>
> > > >>> Since code allocations are now implemented with execmem, kprobes can be
> > > >>> enabled in non-modular kernels.
> > > >>>
> > > >>> Add #ifdef CONFIG_MODULE guards for the code dealing with kprobes inside
> > > >>> modules, make CONFIG_KPROBES select CONFIG_EXECMEM and drop the
> > > >>> dependency of CONFIG_KPROBES on CONFIG_MODULES.
> > > >>
> > > >> Thanks for this work, but this conflicts with the latest fix in v6.9-rc4.
> > > >> Also, can you use IS_ENABLED(CONFIG_MODULES) instead of #ifdefs in
> > > >> function body? We have enough dummy functions for that, so it should
> > > >> not make a problem.
> > > > 
> > > > The code in check_kprobe_address_safe() that gets the module and checks for
> > > > __init functions does not compile with IS_ENABLED(CONFIG_MODULES).
> > > > I can pull it out to a helper or leave #ifdef in the function body,
> > > > whichever you prefer.
> > > 
> > > As far as I can see, the only problem is MODULE_STATE_COMING.
> > > Can we move 'enum module_state' out of #ifdef CONFIG_MODULES in module.h  ?
> > 
> > There's dereference of 'struct module' there:
> >  
> > 		(*probed_mod)->state != MODULE_STATE_COMING) {
> > 			...
> > 		}
> > 
> > so moving out 'enum module_state' won't be enough.
> 
> Hmm, this part should be inline functions like;
> 
> #ifdef CONFIG_MODULES
> static inline bool module_is_coming(struct module *mod)
> {
> 	return mod->state == MODULE_STATE_COMING;
> }
> #else
> #define module_is_coming(mod) (false)

I'd prefer

static inline module_is_coming(struct module *mod)
{
	return false;
}

> #endif
>
> Then we don't need the enum.
> Thank you,
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>

-- 
Sincerely yours,
Mike.