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

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Message-Id: <20180419105556.86664-1-tmricht@linux.ibm.com>
Date:   Thu, 19 Apr 2018 12:55:56 +0200
From:   Thomas Richter <tmricht@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     heiko.carstens@...ibm.com, brueckner@...ux.vnet.ibm.com,
        schwidefsky@...ibm.com, Thomas Richter <tmricht@...ux.ibm.com>,
        stable@...r.kernel.org,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        David S Miller <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>, acme@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH] kprobes: Fix random address output of blacklist file

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.

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?

Fixes: ad67b74d2469 ("printk: hash addresses printed with %p")
Cc: <stable@...r.kernel.org> # v4.15+
Cc: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Cc: David S Miller <davem@...emloft.net>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: acme@...nel.org
Cc: 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