[RFC][kprobe](djprobe) djprobe examples

[Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>]

Hi,

I also updated djprobe example code.
I attached it and a helper script.

NOTE:
Currently, this helper script can ONLY measure the *LENGTH* of the
instruction-block which will be overwritten by a jump code. It can
*NOT CHECK* whether this instruction-block can be executed out of
line (relocatable) and no branch jumps into the target area.
However, now we're developing more useful helper tool which can
check it.

Here is the example of usage;
1) Analyze the kernel code by using the helper script.
$ ./disym.sh sys_symlink
sys_symlink
0xc017bbe0

/lib/modules/2.6.19-rc1-mm1/build/vmlinux:     file format elf32-i386

Disassembly of section .text:

c017bbe0 <sys_symlink>:
c017bbe0:       83 ec 0c                sub    $0xc,%esp
c017bbe3:       8b 44 24 14             mov    0x14(%esp),%eax

Please be sure that the above-disassembled instructions are relocatable.
Parameter: addr=0xc017bbe0 size=7


2) If the instructions can be executed out of line (ex. load/store,
 compare, add/sub, etc.) and no branch jumps into it (you can dump whole
 of the function by using disym.sh with '-a' option),
 Install the example module with the above parameters.

$ sudo /sbin/insmod ./djprobe_ex.ko addr=0xc017bbe0 size=7


3) and test it.

$ ln -s foo bar
$ dmesg | tail -n 4
probe install at c017bbe0, size 7
Stopping tasks: =======================================|
Restarting tasks... done
probe call:c017bbe0, caller:c01030c5

$ rm bar
$ ln -s foo bar
$ dmesg | tail -n 5
probe install at c017bbe0, size 7
Stopping tasks: =======================================|
Restarting tasks... done
probe call:c017bbe0, caller:c01030c5
probe call:c017bbe0, caller:c01030c5

4) Finally, remove the module.

$ sudo /sbin/rmmod djprobe_ex.ko
$ dmesg | tail -n 8
probe install at c017bbe0, size 7
Stopping tasks: =======================================|
Restarting tasks... done
probe call:c017bbe0, caller:c01030c5
probe call:c017bbe0, caller:c01030c5
probe uninstall at c017bbe0
Stopping tasks: =======================================|
Restarting tasks... done


Thanks,

-- 
Masami HIRAMATSU
Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com

#!/bin/sh
# Copyright (C) HITACHI, Ltd. 2005
# Created by M.Hiramatsu <hiramatu@sdl.hitachi.co.jp>

[ $# -gt 3 -o $# -lt 1 ] && echo "usage: disym.sh [-a] <kernel_symbol> [kernel-version]" && exit 0

DISALL=0
if [ $1 = "-a" ] ;then
DISALL=1
shift 1
fi

SYM=$1
KVER=$2
[ -z "$KVER" ] && KVER=`uname -r`

function cntarg () {
return $#
}

SYSMAP=/lib/modules/$KVER/build/System.map
[ -f $SYSMAP ] || SYSMAP=/boot/System.map-`uname -r`
[ -f $SYSMAP ] || SYSMAP=/proc/kallsyms

VMLINUX=/lib/modules/$KVER/build/vmlinux
[ -f $VMLINUX ] || VMLINUX=/boot/vmlinux-`uname -r`
[ -f $VMLINUX ] || VMLINUX=/usr/lib/debug/lib/modules/$KVER/vmlinux

setaddrs () {
XADDR=$1
XEADDR=$2
}

echo $SYM
case $SYM in
	0x*)
	XADDR=$SYM
	SADDR=`printf "%d" $SYM`
	EADDR=`expr $SADDR + 5`
	;;
	*)
	if [ $DISALL -eq 1 ] ;then
	setaddrs `sort $SYSMAP | grep -A1 " $SYM"$  | cut -f 1 -d\ `
	if [ -z "$XADDR" ] ; then 
		echo "Error : $SYM was not found in "$SYSMAP
		exit 0;
	fi
	XADDR=0x$XADDR
	XEADDR=0x$XEADDR
	SADDR=`printf "%d" $XADDR` 
	EADDR=`printf "%d" $XEADDR` 
	else
	XADDR=0x`grep " $SYM"$ $SYSMAP | cut -f 1 -d\ `
	if [ "$XADDR" = "0x" ] ; then 
		echo "Error : $SYM was not found in "$SYSMAP
		exit 0;
	fi
	SADDR=`printf "%d" $XADDR` 
	EADDR=`expr $SADDR + 5`
	fi
	;;
esac
echo $XADDR

objdump -w --start-address=$SADDR --stop-address=$EADDR -j ".text" -d $VMLINUX
echo 
LLINE=`objdump -w --start-address=$SADDR --stop-address=$EADDR -j ".text" -d $VMLINUX | tail -n 1 | sed s/"	"/\:/g`
EXADDR=`echo $LLINE | cut -f 1 -d:`
cntarg `echo $LLINE | cut -f 3 -d:`
DIFF=$?
EADDR=`printf "%d" 0x$EXADDR`
SIZE=`expr $EADDR - $SADDR + $DIFF`
echo "Please be sure that the above-disassembled instructions are relocatable."
echo "Parameter: addr=$XADDR size=$SIZE"

/* 
 djprobe_ex.c -- Direct Jump Probe Example
 Copyright (c) 2005,2006 Hitachi,Ltd.,
 Created by Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 2 of the License, or
 (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
#include <linux/version.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/rcupdate.h>
#include <linux/kprobes.h>

static long addr=0;
module_param(addr, long, 0444);
static long offs=0;
module_param(offs, long, 0444);
static long size=0;
module_param(size, long, 0444);
static long show_arg=0;
module_param(show_arg, long, 0444);

#define CALLER(regs) (((unsigned long *)&regs->esp)[0])
#define ARG(n,regs) (((unsigned long *)&regs->esp)[n]) /*arg1: ARG(1,stadr)*/

static int probe_func(struct kprobe *kp, struct pt_regs *regs)
{
	int i;
	printk("probe call:%p, caller:%lx", 
	       (void*)kp->addr, CALLER(regs));
	for (i = 1; i <= show_arg; i++) {
		printk(" arg[%d]:%lx", i, ARG(i, regs));
	}
	printk("\n");
	return 0;
}

static struct kprobe kp;

static int install_probe(void) 
{
	if (addr == 0) {
		return -EINVAL;
	}
	printk("probe install at 0x%p+0x%lx, size %ld\n", 
	       (void*)addr, offs, size);

	kp.pre_handler = probe_func;
	kp.addr = (void *)addr;
	kp.length = size;
	if (register_kprobe(&kp) != 0) return -1;
	commit_kprobes();
	return 0;
}

static void uninstall_probe(void)
{
	unregister_kprobe(&kp);
	printk("probe uninstall at %p\n", (void*)addr);
	commit_kprobes();	/* commit for safety */
}

module_init(install_probe);
module_exit(uninstall_probe);
MODULE_AUTHOR("M.Hiramatsu <masami.hiramatsu.pt@hitachi.com>");
MODULE_LICENSE("GPL");