linux-kernel - Re: [PATCH] kprobes: Fix random address output of blacklist file

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Date:   Thu, 26 Apr 2018 17:01:44 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Thomas Richter <tmricht@...ux.ibm.com>
Cc:     ananth@...ux.vnet.ibm.com, anil.s.keshavamurthy@...el.com,
        davem@...emloft.net, akpm@...ux-foundation.org, acme@...nel.org,
        rostedt@...dmis.org, brueckner@...ux.vnet.ibm.com,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes: Fix random address output of blacklist file

On Thu, 26 Apr 2018 09:19:59 +0200
Thomas Richter <tmricht@...ux.ibm.com> wrote:

> File /sys/kernel/debug/kprobes/blacklist displays random addresses:
> 
> [root@...60046 linux]# cat /sys/kernel/debug/kprobes/blacklist
> 0x0000000047149a90-0x00000000bfcb099a	print_type_x8
> ....
> 
> This breaks 'perf probe' which uses the blacklist file to prohibit
> probes on certain functions by checking the address range.
> 
> Fix this by printing the correct (unhashed) address.

Yeah, but I'm not sure recent "%px" policy. I think if the user can
dump kallsyms, this also can be dumped. But kallsyms seems different
policy...

Anyway, please check my series.

https://patchwork.kernel.org/patch/10183629/

It uses to check the kallsyms policy function to check.

Unfortunately, this is not merged. Anyway, I'll repost it (on the top of tip tree)

> 
> The file mode is read all but this is not an issue as the file
> hierarchy points out:
>  # ls -ld /sys/ /sys/kernel/ /sys/kernel/debug/ /sys/kernel/debug/kprobes/
> 	/sys/kernel/debug/kprobes/blacklist
> dr-xr-xr-x 12 root root 0 Apr 19 07:56 /sys/
> drwxr-xr-x  8 root root 0 Apr 19 07:56 /sys/kernel/
> drwx------ 16 root root 0 Apr 19 06:56 /sys/kernel/debug/
> drwxr-xr-x  2 root root 0 Apr 19 06:56 /sys/kernel/debug/kprobes/
> -r--r--r--  1 root root 0 Apr 19 06:56 /sys/kernel/debug/kprobes/blacklist
> 
> Everything in and below /sys/kernel/debug is rwx to root only,
> no group or others have access.
> 
> Background:
> Directory /sys/kernel/debug/kprobes is created by debugfs_create_dir()
> which sets the mode bits to rwxr-xr-x. Maybe change that to use the
> parent's directory mode bits instead?

Good catch! Yes, it should be hardened. 
Anyway, that is out of this topic. I just change blacklist file mode bits
in my series.

Thank you,

> 
> Fixes: ad67b74d2469 ("printk: hash addresses printed with %p")
> Cc: <stable@...r.kernel.org> # v4.15+
> Cc: <linux-kernel@...r.kernel.org>
> To: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
> To: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
> To: David S Miller <davem@...emloft.net>
> To: Masami Hiramatsu <mhiramat@...nel.org>
> To: Andrew Morton <akpm@...ux-foundation.org>
> To: acme@...nel.org
> To: Steven Rostedt <rostedt@...dmis.org>
> 
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> ---
>  kernel/kprobes.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 102160ff5c66..ea619021d901 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2428,7 +2428,7 @@ static int kprobe_blacklist_seq_show(struct seq_file *m, void *v)
>  	struct kprobe_blacklist_entry *ent =
>  		list_entry(v, struct kprobe_blacklist_entry, list);
>  
> -	seq_printf(m, "0x%p-0x%p\t%ps\n", (void *)ent->start_addr,
> +	seq_printf(m, "0x%px-0x%px\t%ps\n", (void *)ent->start_addr,
>  		   (void *)ent->end_addr, (void *)ent->start_addr);
>  	return 0;
>  }
> -- 
> 2.14.3
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>