Re: [PATCH v2 1/4] kprobes: delay blacklist symbol lookup until we actually need it

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

Hello, Oskar.

On Thu, Apr 04, 2013 at 02:51:26PM +0200, Oskar Andero wrote:
> From: Toby Collett <toby.collett@sonymobile.com>
> 
> The symbol lookup can take a long time and kprobes is
> initialised very early in boot, so delay symbol lookup
> until the blacklist is first used.
> 
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: David S. Miller <davem@davemloft.net>
> Reviewed-by: Radovan Lekanovic <radovan.lekanovic@sonymobile.com>
> Signed-off-by: Toby Collett <toby.collett@sonymobile.com>
> Signed-off-by: Oskar Andero <oskar.andero@sonymobile.com>
> ---
>  kernel/kprobes.c | 98 ++++++++++++++++++++++++++++++++++----------------------
>  1 file changed, 60 insertions(+), 38 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index e35be53..0a270e5 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -68,6 +68,7 @@
>  #endif
>  
>  static int kprobes_initialized;
> +static int kprobe_blacklist_initialized;
>  static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
>  static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
>  
> @@ -102,6 +103,60 @@ static struct kprobe_blackpoint kprobe_blacklist[] = {
>  	{NULL}    /* Terminator */
>  };
>  
> +/* it can take some time ( > 100ms ) to initialise the
> + * blacklist so we delay this until we actually need it
> + */
> +static void init_kprobe_blacklist(void)
> +{
> +	int i;
> +	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;
> +	}
> +
> +	if (kretprobe_blacklist_size) {
> +		/* lookup the function address from its name */
> +		for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
> +			kprobe_lookup_name(kretprobe_blacklist[i].name,
> +					   kretprobe_blacklist[i].addr);
> +			if (!kretprobe_blacklist[i].addr)
> +				printk("kretprobe: lookup failed: %s\n",
> +				       kretprobe_blacklist[i].name);
> +		}
> +	}
> +	kprobe_blacklist_initialized = 1;

You need smp_wmb() before assigning 'kprobe_blacklist_initialized = 1'.
This guarantee that who see kprobe_blacklist_initialized = 1 will get
updated data of kprobe_blacklist.

Please refer my previous patch once more :)

And How about define kprobe_blacklist_initialized as boolean?

Thanks.

> +
> +out:
> +	mutex_unlock(&kprobe_mutex);
> +}
> +
>  #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
>  /*
>   * kprobe->ainsn.insn points to the copy of the instruction to be
> @@ -1331,6 +1386,9 @@ 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 (unlikely(!kprobe_blacklist_initialized))
> +		init_kprobe_blacklist();
>  	/*
>  	 * If there exists a kprobe_blacklist, verify and
>  	 * fail any probe registration in the prohibited area
> @@ -1816,6 +1874,8 @@ int __kprobes register_kretprobe(struct kretprobe *rp)
>  	void *addr;
>  
>  	if (kretprobe_blacklist_size) {
> +		if (unlikely(!kprobe_blacklist_initialized))
> +			init_kprobe_blacklist();
>  		addr = kprobe_addr(&rp->kp);
>  		if (IS_ERR(addr))
>  			return PTR_ERR(addr);
> @@ -2065,11 +2125,6 @@ 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 */
> @@ -2079,39 +2134,6 @@ 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++) {
> -			kprobe_lookup_name(kretprobe_blacklist[i].name,
> -					   kretprobe_blacklist[i].addr);
> -			if (!kretprobe_blacklist[i].addr)
> -				printk("kretprobe: lookup failed: %s\n",
> -				       kretprobe_blacklist[i].name);
> -		}
> -	}
> -
>  #if defined(CONFIG_OPTPROBES)
>  #if defined(__ARCH_WANT_KPROBES_INSN_SLOT)
>  	/* Init kprobe_optinsn_slots */
> -- 
> 1.8.1.5
> 
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