Re: [PATCH v2 4/4] kprobes: Remove core dependency on modules

[Jarkko Sakkinen]

On Wed Apr 3, 2024 at 6:01 PM EEST, Mark Rutland wrote:
> From: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
>
> Tracing with kprobes while running a monolithic kernel is currently
> impossible because KPROBES depends on MODULES. While this dependency is
> necessary when HAVE_KPROBES_ALLOC=n and the core kprobes code allocates
> memory using module_alloc(), all the other module-specific code only
> exist to handle the case when MODULES=y, and can be hidden behind
> ifdeffery.
>
> Add the necessary ifdeffery, and remove the dependency on MODULES=y when
> HAVE_KPROBES_ALLOC=y.
>
> As of this patch kprobes can be used when MODULES=n on arm64 and
> riscv. All other architectures still depend on MODULES, either by virtue
> of the core dependency on MODULES when HAVE_KPROBES_ALLOC=n, or by
> virtue of an explciit dependency on MODULES in arch code.
>
> Other architectures can enable support by implementing their own
> kprobes_alloc_insn_page() and kprobes_free_insn_page() which do not
> depend on MODULES.
>
> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/20240326134616.7691-1-jarkko@xxxxxxxxxx/
> [Mark: Remove execmem changes, depend on HAVE_KPROBES_ALLOC]
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> ---
>  arch/Kconfig                |  2 +-
>  kernel/kprobes.c            | 46 ++++++++++++++++++++++---------------
>  kernel/trace/trace_kprobe.c | 15 ++++++++++--
>  3 files changed, 41 insertions(+), 22 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 85bb59f7b8c07..0df2c88547b3c 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -52,7 +52,7 @@ config GENERIC_ENTRY
>  
>  config KPROBES
>  	bool "Kprobes"
> -	depends on MODULES
> +	depends on MODULES || HAVE_KPROBES_ALLOC
>  	depends on HAVE_KPROBES
>  	select KALLSYMS
>  	select TASKS_RCU if PREEMPTION
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index fa2ee4e59eca2..ec4493a41b505 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1594,6 +1594,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  			goto out;
>  		}
>  
> +#ifdef CONFIG_MODULES
>  		/*
>  		 * If the module freed '.init.text', we couldn't insert
>  		 * kprobes in there.
> @@ -1604,7 +1605,9 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  			*probed_mod = NULL;
>  			ret = -ENOENT;
>  		}
> +#endif /* CONFIG_MODULES */
>  	}
> +
>  out:
>  	preempt_enable();
>  	jump_label_unlock();
> @@ -2484,24 +2487,6 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
>  	return 0;
>  }
>  
> -/* Remove all symbols in given area from kprobe blacklist */
> -static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> -{
> -	struct kprobe_blacklist_entry *ent, *n;
> -
> -	list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> -		if (ent->start_addr < start || ent->start_addr >= end)
> -			continue;
> -		list_del(&ent->list);
> -		kfree(ent);
> -	}
> -}
> -
> -static void kprobe_remove_ksym_blacklist(unsigned long entry)
> -{
> -	kprobe_remove_area_blacklist(entry, entry + 1);
> -}
> -
>  int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
>  				   char *type, char *sym)
>  {
> @@ -2566,6 +2551,25 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
>  	return ret ? : arch_populate_kprobe_blacklist();
>  }
>  
> +#ifdef CONFIG_MODULES
> +/* Remove all symbols in given area from kprobe blacklist */
> +static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> +{
> +	struct kprobe_blacklist_entry *ent, *n;
> +
> +	list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
> +		if (ent->start_addr < start || ent->start_addr >= end)
> +			continue;
> +		list_del(&ent->list);
> +		kfree(ent);
> +	}
> +}
> +
> +static void kprobe_remove_ksym_blacklist(unsigned long entry)
> +{
> +	kprobe_remove_area_blacklist(entry, entry + 1);
> +}
> +
>  static void add_module_kprobe_blacklist(struct module *mod)
>  {
>  	unsigned long start, end;
> @@ -2662,6 +2666,9 @@ static int kprobes_module_callback(struct notifier_block *nb,
>  	mutex_unlock(&kprobe_mutex);
>  	return NOTIFY_DONE;
>  }
> +#else
> +#define kprobes_module_callback	(NULL)
> +#endif /* CONFIG_MODULES */
>  
>  static struct notifier_block kprobe_module_nb = {
>  	.notifier_call = kprobes_module_callback,
> @@ -2726,7 +2733,8 @@ 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);
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 14099cc17fc9e..c509ba776e679 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -111,6 +111,7 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
>  	return strncmp(module_name(mod), name, len) == 0 && name[len] == ':';
>  }
>  
> +#ifdef CONFIG_MODULES
>  static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
>  {
>  	char *p;
> @@ -129,6 +130,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
>  
>  	return ret;
>  }
> +#else
> +#define trace_kprobe_module_exist(tk) false /* aka a module never exists */
> +#endif /* CONFIG_MODULES */
>  
>  static bool trace_kprobe_is_busy(struct dyn_event *ev)
>  {
> @@ -670,6 +674,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
>  	return ret;
>  }
>  
> +#ifdef CONFIG_MODULES
>  /* Module notifier call back, checking event on the module */
>  static int trace_kprobe_module_callback(struct notifier_block *nb,
>  				       unsigned long val, void *data)
> @@ -699,6 +704,9 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
>  
>  	return NOTIFY_DONE;
>  }
> +#else
> +#define trace_kprobe_module_callback (NULL)
> +#endif /* CONFIG_MODULES */
>  
>  static struct notifier_block trace_kprobe_module_nb = {
>  	.notifier_call = trace_kprobe_module_callback,
> @@ -1933,8 +1941,11 @@ static __init int init_kprobe_trace_early(void)
>  	if (ret)
>  		return ret;
>  
> -	if (register_module_notifier(&trace_kprobe_module_nb))
> -		return -EINVAL;
> +	if (IS_ENABLED(CONFIG_MODULES)) {
> +		ret = register_module_notifier(&trace_kprobe_module_nb);
> +		if (ret)
> +			return -EINVAL;
> +	}
>  
>  	return 0;
>  }

2/4, 3/4, 4/4:

Tested-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> # arch/riscv

BR, Jarkko