Re: [PATCH] kprobe: initialize kprobe_blacklist when it is used firstly

[Masami Hiramatsu]

Hi,

(2013/04/01 15:55), Joonsoo Kim wrote:
> Currently, initializing kprobe_blacklist is done during boot process.
> It takes 230 ms on our android platform and this is significant amount
> for our use case. We can disable CONFIG_KPROBES for production kernel,
> but it is hassle. This kprobe functionality is not commonly used,
> so we don't need to pay this cost at all times. With this rationale,
> change code to initialize kprobe_blacklist when it is used firstly.

I saw similar patch from Oskar and Toby, and I decided to wait
until his blacklist separating work. I'd like to ask Oskar
how the patch is going first.

Thank you,

> 
> Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
> I fotgot to add lkml.
> Sorry for noise.
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index e35be53..5e90092 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -101,6 +101,7 @@ static struct kprobe_blackpoint kprobe_blacklist[] = {
>  	{"mcount",},	/* mcount can be called from everywhere */
>  	{NULL}    /* Terminator */
>  };
> +static bool kprobe_blacklist_initialized;
>  
>  #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
>  /*
> @@ -1324,6 +1325,49 @@ out:
>  	return ret;
>  }
>  
> +static void __kprobes init_kprobe_blacklist(void)
> +{
> +	unsigned long offset = 0, size = 0;
> +	char *modname, namebuf[128];
> +	const char *symbol_name;
> +	void *addr;
> +	struct kprobe_blackpoint *kb;
> +
> +	mutex_lock(&kprobe_mutex);
> +	if (kprobe_blacklist_initialized)
> +		goto out;
> +
> +	/*
> +	 * Lookup and populate the kprobe_blacklist.
> +	 *
> +	 * Unlike the kretprobe blacklist, we'll need to determine
> +	 * the range of addresses that belong to the said functions,
> +	 * since a kprobe need not necessarily be at the beginning
> +	 * of a function.
> +	 */
> +	for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
> +		kprobe_lookup_name(kb->name, addr);
> +		if (!addr)
> +			continue;
> +
> +		kb->start_addr = (unsigned long)addr;
> +		symbol_name = kallsyms_lookup(kb->start_addr,
> +				&size, &offset, &modname, namebuf);
> +		if (!symbol_name)
> +			kb->range = 0;
> +		else
> +			kb->range = size;
> +	}
> +
> +	/* This guarantee that who see initilized will
> +	 * get a updated data of kprobe_blacklist */
> +	smp_wmb();
> +	kprobe_blacklist_initialized = true;
> +
> +out:
> +	mutex_unlock(&kprobe_mutex);
> +}
> +
>  static int __kprobes in_kprobes_functions(unsigned long addr)
>  {
>  	struct kprobe_blackpoint *kb;
> @@ -1331,6 +1375,7 @@ static int __kprobes in_kprobes_functions(unsigned long addr)
>  	if (addr >= (unsigned long)__kprobes_text_start &&
>  	    addr < (unsigned long)__kprobes_text_end)
>  		return -EINVAL;
> +
>  	/*
>  	 * If there exists a kprobe_blacklist, verify and
>  	 * fail any probe registration in the prohibited area
> @@ -1476,6 +1521,9 @@ int __kprobes register_kprobe(struct kprobe *p)
>  	struct module *probed_mod;
>  	kprobe_opcode_t *addr;
>  
> +	if (unlikely(!kprobe_blacklist_initialized))
> +		init_kprobe_blacklist();
> +
>  	/* Adjust probe address from symbol */
>  	addr = kprobe_addr(p);
>  	if (IS_ERR(addr))
> @@ -2065,11 +2113,6 @@ static struct notifier_block kprobe_module_nb = {
>  static int __init init_kprobes(void)
>  {
>  	int i, err = 0;
> -	unsigned long offset = 0, size = 0;
> -	char *modname, namebuf[128];
> -	const char *symbol_name;
> -	void *addr;
> -	struct kprobe_blackpoint *kb;
>  
>  	/* FIXME allocate the probe table, currently defined statically */
>  	/* initialize all list heads */
> @@ -2079,28 +2122,6 @@ static int __init init_kprobes(void)
>  		raw_spin_lock_init(&(kretprobe_table_locks[i].lock));
>  	}
>  
> -	/*
> -	 * Lookup and populate the kprobe_blacklist.
> -	 *
> -	 * Unlike the kretprobe blacklist, we'll need to determine
> -	 * the range of addresses that belong to the said functions,
> -	 * since a kprobe need not necessarily be at the beginning
> -	 * of a function.
> -	 */
> -	for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
> -		kprobe_lookup_name(kb->name, addr);
> -		if (!addr)
> -			continue;
> -
> -		kb->start_addr = (unsigned long)addr;
> -		symbol_name = kallsyms_lookup(kb->start_addr,
> -				&size, &offset, &modname, namebuf);
> -		if (!symbol_name)
> -			kb->range = 0;
> -		else
> -			kb->range = size;
> -	}
> -
>  	if (kretprobe_blacklist_size) {
>  		/* lookup the function address from its name */
>  		for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx


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