linux-kernel - Re: [PATCH v2 2/4] kprobes: split blacklist into common and arch

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Date:	Fri, 05 Apr 2013 11:34:27 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Oskar Andero <oskar.andero@...ymobile.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	davem@...emloft.net, anil.s.keshavamurthy@...el.com,
	ananth@...ibm.com, radovan.lekanovic@...ymobile.com,
	bjorn.davidsson@...ymobile.com,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: [PATCH v2 2/4] kprobes: split blacklist into common and arch

(2013/04/04 21:51), Oskar Andero wrote:
> Some blackpoints are only valid for specific architectures. To let each
> architecture specify its own blackpoints the list has been split in two
> lists: common and arch. The common list is kept in kernel/kprobes.c and
> the arch list is kept in the arch/ directory.
> 

Here I missed one racing issue.

> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 0a270e5..7654278 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
[...]
>  
>  /* 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;
> +	int i, j = 0;
>  
>  	mutex_lock(&kprobe_mutex);
> -	if (kprobe_blacklist_initialized)
> +	if (kprobe_blacklist)
>  		goto out;
>  
> +	kprobe_blacklist_size = common_kprobes_blacksyms_size +
> +				arch_kprobes_blacksyms_size;
> +	kprobe_blacklist = kzalloc(sizeof(*kprobe_blacklist) *
> +				   kprobe_blacklist_size, GFP_KERNEL);

If you'd like to use kprobe_blacklist itself as an initialized flag,
you must prepare the "blacklist" local pointer to allocate and
initialize entries.

> @@ -151,7 +175,6 @@ static void init_kprobe_blacklist(void)
>  				       kretprobe_blacklist[i].name);
>  		}
>  	}
> -	kprobe_blacklist_initialized = 1;

And after initialized, assign blacklist to kprobe_blacklist.

Without that, other thread may refer the uninitialized (but allocated)
black list.

Thank you,

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


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