Re: [PATCH RFC] kprobes: Remove MODULES dependency

[Jarkko Sakkinen]

On Fri, Jul 10, 2020 at 07:32:57PM +0900, Masami Hiramatsu wrote:
> Hi Jarkko,
> 
> On Fri, 10 Jul 2020 02:45:19 +0300
> Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> 
> > Remove MODULES dependency and migrate from module_alloc to vmalloc().
> > According to Andi, the history with this dependency is that kprobes
> > originally required custom LKM's, which does not hold today anymore.
> > 
> > Right now one has to compile LKM support only to enable kprobes.  With
> > this change applied, it is somewhat easier to create custom test
> > kernel's with a proper debugging capabilities, thus making Linux more
> > developer friendly.
> 
> Agreed. Now we have several way to access kprobes via ftrace/perf/bpf
> without modules. So it's a good time to remove CONFIG_MODULE dependency.
> 
> But I also would like to minimize the changes for code readability.
> I made some comments below.

Thanks, appreciate this.

> > Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> > ---
> >  arch/Kconfig                   |  1 -
> >  arch/x86/kernel/kprobes/core.c |  5 +++--
> >  kernel/kprobes.c               | 22 ++++++++++++++++++++--
> >  kernel/trace/trace_kprobe.c    | 12 ++++++++++++
> >  4 files changed, 35 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 8cc35dc556c7..bb59cdf335ab 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -61,7 +61,6 @@ config OPROFILE_NMI_TIMER
> >  
> >  config KPROBES
> >  	bool "Kprobes"
> > -	depends on MODULES
> >  	depends on HAVE_KPROBES
> >  	select KALLSYMS
> >  	help
> > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> > index ada39ddbc922..dc7b8d6fd20d 100644
> > --- a/arch/x86/kernel/kprobes/core.c
> > +++ b/arch/x86/kernel/kprobes/core.c
> > @@ -42,6 +42,7 @@
> >  #include <linux/moduleloader.h>
> >  #include <linux/vmalloc.h>
> >  #include <linux/pgtable.h>
> > +#include <linux/vmalloc.h>
> >  
> >  #include <asm/text-patching.h>
> >  #include <asm/cacheflush.h>
> > @@ -423,7 +424,7 @@ void *alloc_insn_page(void)
> >  {
> >  	void *page;
> >  
> > -	page = module_alloc(PAGE_SIZE);
> > +	page = vmalloc(PAGE_SIZE);
> 
> No, you can not use vmalloc here. The reason why we use module_alloc()
> is to allocate the executable memory for trampoline code.
> So, you need to use vmalloc_exec() instead.

Right, I'm on the wagon with this after reading Peter's explanation.

> 
> >  	if (!page)
> >  		return NULL;
> >  
> > @@ -446,7 +447,7 @@ void *alloc_insn_page(void)
> >  /* Recover page to RW mode before releasing it */
> >  void free_insn_page(void *page)
> >  {
> > -	module_memfree(page);
> > +	vfree(page);
> >  }
> >  
> >  static int arch_copy_kprobe(struct kprobe *p)
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 4a904cc56d68..02680642ea11 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -35,6 +35,7 @@
> >  #include <linux/ftrace.h>
> >  #include <linux/cpu.h>
> >  #include <linux/jump_label.h>
> > +#include <linux/vmalloc.h>
> >  
> >  #include <asm/sections.h>
> >  #include <asm/cacheflush.h>
> > @@ -111,12 +112,12 @@ enum kprobe_slot_state {
> >  
> >  void __weak *alloc_insn_page(void)
> >  {
> > -	return module_alloc(PAGE_SIZE);
> > +	return vmalloc(PAGE_SIZE);
> 
> Ditto.
> 
> >  }
> >  
> >  void __weak free_insn_page(void *page)
> >  {
> > -	module_memfree(page);
> > +	vfree(page);
> >  }
> >  
> >  struct kprobe_insn_cache kprobe_insn_slots = {
> > @@ -563,8 +564,11 @@ static void kprobe_optimizer(struct work_struct *work)
> >  	mutex_lock(&kprobe_mutex);
> >  	cpus_read_lock();
> >  	mutex_lock(&text_mutex);
> > +
> > +#ifdef CONFIG_MODULES
> >  	/* Lock modules while optimizing kprobes */
> >  	mutex_lock(&module_mutex);
> > +#endif
> 
> Hmm, can you reduce these "#ifdef CONFIG_MODULE"s ?
> 
> e.g. 
> 
> #ifdef CONFIG_MODULES
> static void lock_modules(void)
> {
> 	mutex_lock(&module_mutex);
> }
> ...
> #else
> #define lock_modules() do { } while (0)
> ...
> #endif

Yes, I'll use this idea also to address to issues reported below.

> 
> >  
> >  	/*
> >  	 * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
> > @@ -589,7 +593,9 @@ static void kprobe_optimizer(struct work_struct *work)
> >  	/* Step 4: Free cleaned kprobes after quiesence period */
> >  	do_free_cleaned_kprobes();
> >  
> > +#ifdef CONFIG_MODULES
> >  	mutex_unlock(&module_mutex);
> > +#endif
> >  	mutex_unlock(&text_mutex);
> >  	cpus_read_unlock();
> >  
> > @@ -739,6 +745,7 @@ static int reuse_unused_kprobe(struct kprobe *ap)
> >  	return 0;
> >  }
> >  
> 
> > +#ifdef CONFIG_MODULE
> >  /* Remove optimized instructions */
> >  static void kill_optimized_kprobe(struct kprobe *p)
> >  {
> > @@ -764,6 +771,7 @@ static void kill_optimized_kprobe(struct kprobe *p)
> >  	/* Don't touch the code, because it is already freed. */
> >  	arch_remove_optimized_kprobe(op);
> >  }
> > +#endif
> 
> This optprobe related one is OK to keep in this place. 
> 
> >  
> >  static inline
> >  void __prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
> > @@ -1608,6 +1616,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> >  			goto out;
> >  		}
> >  
> > +#ifdef CONFIG_MODULE
> >  		/*
> >  		 * If the module freed .init.text, we couldn't insert
> >  		 * kprobes in there.
> > @@ -1618,6 +1627,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> >  			*probed_mod = NULL;
> >  			ret = -ENOENT;
> >  		}
> > +#endif
> >  	}
> >  out:
> >  	preempt_enable();
> > @@ -2090,6 +2100,7 @@ NOKPROBE_SYMBOL(pre_handler_kretprobe);
> >  
> >  #endif /* CONFIG_KRETPROBES */
> >  
> > +#ifdef CONFIG_MODULE
> >  /* Set the kprobe gone and remove its instruction buffer. */
> >  static void kill_kprobe(struct kprobe *p)
> >  {
> > @@ -2114,6 +2125,7 @@ static void kill_kprobe(struct kprobe *p)
> >  	 */
> >  	arch_remove_kprobe(p);
> >  }
> > +#endif
> >  
> >  /* Disable one kprobe */
> >  int disable_kprobe(struct kprobe *kp)
> > @@ -2214,6 +2226,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
> >  	return 0;
> >  }
> >  
> > +#ifdef CONFIG_MODULE
> >  /* Remove all symbols in given area from kprobe blacklist */
> >  static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> >  {
> > @@ -2231,6 +2244,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
> >  {
> >  	kprobe_remove_area_blacklist(entry, entry + 1);
> >  }
> > +#endif
> >  
> >  int __init __weak arch_populate_kprobe_blacklist(void)
> >  {
> > @@ -2274,6 +2288,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
> >  	return ret ? : arch_populate_kprobe_blacklist();
> >  }
> >  
> > +#ifdef CONFIG_MODULE
> >  static void add_module_kprobe_blacklist(struct module *mod)
> >  {
> >  	unsigned long start, end;
> > @@ -2375,6 +2390,7 @@ static struct notifier_block kprobe_module_nb = {
> >  	.notifier_call = kprobes_module_callback,
> >  	.priority = 0
> >  };
> > +#endif /* CONFIG_MODULE */
> >  
> >  /* Markers of _kprobe_blacklist section */
> >  extern unsigned long __start_kprobe_blacklist[];
> > @@ -2425,8 +2441,10 @@ static int __init init_kprobes(void)
> >  	err = arch_init_kprobes();
> >  	if (!err)
> >  		err = register_die_notifier(&kprobe_exceptions_nb);
> > +#ifdef CONFIG_MODULE
> >  	if (!err)
> >  		err = register_module_notifier(&kprobe_module_nb);
> > +#endif
> >  
> >  	kprobes_initialized = (err == 0);
> >  
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index aefb6065b508..30969b38fce8 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -103,6 +103,7 @@ static nokprobe_inline bool trace_kprobe_has_gone(struct trace_kprobe *tk)
> >  	return !!(kprobe_gone(&tk->rp.kp));
> >  }
> >  
> > +#ifdef CONFIG_MODULE
> >  static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> >  						 struct module *mod)
> >  {
> > @@ -110,7 +111,9 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> >  	const char *name = trace_kprobe_symbol(tk);
> >  	return strncmp(mod->name, name, len) == 0 && name[len] == ':';
> >  }
> > +#endif
> >  
> > +#ifdef CONFIG_MODULE
> >  static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> >  {
> >  	char *p;
> > @@ -129,6 +132,7 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> >  
> >  	return ret;
> >  }
> > +#endif
> 
> Here, too. If you make a dummy function in case of !CONFIG_MODULE,
> we don't need to modify caller-side code.
> 
> >  
> >  static bool trace_kprobe_is_busy(struct dyn_event *ev)
> >  {
> > @@ -608,10 +612,12 @@ static int append_trace_kprobe(struct trace_kprobe *tk, struct trace_kprobe *to)
> >  
> >  	/* Register k*probe */
> >  	ret = __register_trace_kprobe(tk);
> > +#ifdef CONFIG_MODULE
> >  	if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
> >  		pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
> >  		ret = 0;
> >  	}
> > +#endif
> 
> So, please make a dummy trace_kprobe_module_exist() and keep this untouched.
> 
> >  
> >  	if (ret)
> >  		trace_probe_unlink(&tk->tp);
> > @@ -651,10 +657,12 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
> >  
> >  	/* Register k*probe */
> >  	ret = __register_trace_kprobe(tk);
> > +#ifdef CONFIG_MODULE
> >  	if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
> >  		pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
> >  		ret = 0;
> >  	}
> > +#endif
> 
> Ditto.
> 
> >  
> >  	if (ret < 0)
> >  		unregister_kprobe_event(tk);
> > @@ -666,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
> >  	return ret;
> >  }
> >  
> > +#ifdef CONFIG_MODULE
> >  /* Module notifier call back, checking event on the module */
> >  static int trace_kprobe_module_callback(struct notifier_block *nb,
> >  				       unsigned long val, void *data)
> > @@ -700,6 +709,7 @@ static struct notifier_block trace_kprobe_module_nb = {
> >  	.notifier_call = trace_kprobe_module_callback,
> >  	.priority = 1	/* Invoked after kprobe module callback */
> >  };
> > +#endif
> 
> Unless it makes any build error, please keep it untouched.
> 
> >  
> >  /* Convert certain expected symbols into '_' when generating event names */
> >  static inline void sanitize_event_name(char *name)
> > @@ -1891,8 +1901,10 @@ static __init int init_kprobe_trace_early(void)
> >  	if (ret)
> >  		return ret;
> >  
> > +#ifdef CONFIG_MODULE
> >  	if (register_module_notifier(&trace_kprobe_module_nb))
> >  		return -EINVAL;
> > +#endif
> 
> Ditto.
> 
> Thank you,

Thanks a lot for the remarks.

> 
> >  
> >  	return 0;
> >  }
> > -- 
> > 2.25.1
> > 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@xxxxxxxxxx>

/Jarkko