linux-kernel - Re: [RFC][PATCH 3/4] kprobes: Allow kprobes with CONFIG

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Date: Fri, 8 Mar 2024 12:36:02 -0800
From: Calvin Owens <jcalvinowens@...il.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Naveen N Rao <naveen.n.rao@...ux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	David S Miller <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>, bpf@...r.kernel.org,
	linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 3/4] kprobes: Allow kprobes with CONFIG_MODULES=n

On Thursday 03/07 at 09:22 +0200, Mike Rapoport wrote:
> On Wed, Mar 06, 2024 at 12:05:10PM -0800, Calvin Owens wrote:
> > If something like this is merged down the road, it can go in at leisure
> > once the module_alloc change is in: it's a one-way dependency.
> > 
> > Signed-off-by: Calvin Owens <jcalvinowens@...il.com>
> > ---
> >  arch/Kconfig                |  2 +-
> >  kernel/kprobes.c            | 22 ++++++++++++++++++++++
> >  kernel/trace/trace_kprobe.c | 11 +++++++++++
> >  3 files changed, 34 insertions(+), 1 deletion(-)
> 
> When I did this in my last execmem posting, I think I've got slightly less
> ugly ifdery, you may want to take a look at that:
> 
> https://lore.kernel.org/all/20230918072955.2507221-13-rppt@kernel.org

Thanks Mike, I definitely agree. I'm annoyed at myself for not finding
your patches, I spent some time looking for prior work and I really
don't know how I missed it...

> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index cfc24ced16dd..e60ce984d095 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -52,8 +52,8 @@ config GENERIC_ENTRY
> >  
> >  config KPROBES
> >  	bool "Kprobes"
> > -	depends on MODULES
> >  	depends on HAVE_KPROBES
> > +	select MODULE_ALLOC
> >  	select KALLSYMS
> >  	select TASKS_RCU if PREEMPTION
> >  	help
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 9d9095e81792..194270e17d57 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1556,8 +1556,12 @@ static bool is_cfi_preamble_symbol(unsigned long addr)
> >  		str_has_prefix("__pfx_", symbuf);
> >  }
> >  
> > +#if IS_ENABLED(CONFIG_MODULES)
> >  static int check_kprobe_address_safe(struct kprobe *p,
> >  				     struct module **probed_mod)
> > +#else
> > +static int check_kprobe_address_safe(struct kprobe *p)
> > +#endif
> >  {
> >  	int ret;
> >  
> > @@ -1580,6 +1584,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> >  		goto out;
> >  	}
> >  
> > +#if IS_ENABLED(CONFIG_MODULES)
> 
> Plain #ifdef will do here and below. IS_ENABLED is for usage withing the
> code, like
> 
> 	if (IS_ENABLED(CONFIG_MODULES))
> 		;
> 
> >  	/* Check if 'p' is probing a module. */
> >  	*probed_mod = __module_text_address((unsigned long) p->addr);
> >  	if (*probed_mod) {
> 
> -- 
> Sincerely yours,
> Mike.