kprobe 模块在执行 "echo 0 > /proc/sys/kernel/ftrace_enabled " 后无法工作
kprobe modules cannot work after execute "echo 0 > /proc/sys/kernel/ftrace_enabled "
只是研究一下 ftrace。
TCP 回显程序 运行 在两个主机之间。
当我关闭大开关(echo 0 > /proc/sys/kernel/ftrace_enabled
)时,我自己的kprobe模块也无法工作。在内核日志文件中看不到 printk 消息。此外,pkt 修改操作失败,可以成功接收 pkt。
真的让我很困惑。
我的测试 kprobe 模块在这里:
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/skbuff.h>
#include <linux/inet.h>
/* For each probe you need to allocate a kprobe structure */
static struct kprobe kp = {
.symbol_name = "ip_rcv",
};
/* kprobe pre_handler: called just before the probed instruction is executed */
static int handler_pre(struct kprobe *p, struct pt_regs *regs)
{
struct sk_buff * skb = (struct sk_buff *)(regs->di);
u16 dst_port;
dst_port = ntohs(*((u16*)(skb->head + skb->transport_header + 2)));
if(dst_port == 50000){ //50000 is the TCP port
printk(KERN_INFO "post handler addr 0x%p skb is 0x%d\n",p->addr, regs->di);
// modify one byte to make TCP checksum wrong and drop the pkt.
*((u8*)(skb->head + skb->network_header +7))=0xab;
}
return 0;
}
/* kprobe post_handler: called after the probed instruction is executed */
static void handler_post(struct kprobe *p, struct pt_regs *regs,
unsigned long flags)
{
//printk(KERN_INFO "post handler addr 0x%p skb is 0x%d\n",p->addr, regs->di);
}
/*
* fault_handler: this is called if an exception is generated for any
* instruction within the pre- or post-handler, or when Kprobes
* single-steps the probed instruction.
*/
static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
{
printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
p->addr, trapnr);
/* Return 0 because we don't handle the fault. */
return 0;
}
static int __init kprobe_init(void)
{
int ret;
kp.pre_handler = handler_pre;
kp.post_handler = handler_post;
kp.fault_handler = handler_fault;
ret = register_kprobe(&kp);
if (ret < 0) {
printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
return ret;
}
printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
return 0;
}
static void __exit kprobe_exit(void)
{
unregister_kprobe(&kp);
printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
}
module_init(kprobe_init)
module_exit(kprobe_exit)
MODULE_LICENSE("GPL");
问题已关闭。
其实在sys/kernel/debug/kprobes/list
我们可以得到注册的kprobe列表。我得到这个 xxxxxxxxxxx k ip_rcv+0x0 [FTRACE]
,这意味着这个 kprobe 是 ftrace-based。 ftrace-based 如果禁用 ftrace,kprobe 将无法工作。
只是研究一下 ftrace。
TCP 回显程序 运行 在两个主机之间。
当我关闭大开关(echo 0 > /proc/sys/kernel/ftrace_enabled
)时,我自己的kprobe模块也无法工作。在内核日志文件中看不到 printk 消息。此外,pkt 修改操作失败,可以成功接收 pkt。
真的让我很困惑。
我的测试 kprobe 模块在这里:
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/skbuff.h>
#include <linux/inet.h>
/* For each probe you need to allocate a kprobe structure */
static struct kprobe kp = {
.symbol_name = "ip_rcv",
};
/* kprobe pre_handler: called just before the probed instruction is executed */
static int handler_pre(struct kprobe *p, struct pt_regs *regs)
{
struct sk_buff * skb = (struct sk_buff *)(regs->di);
u16 dst_port;
dst_port = ntohs(*((u16*)(skb->head + skb->transport_header + 2)));
if(dst_port == 50000){ //50000 is the TCP port
printk(KERN_INFO "post handler addr 0x%p skb is 0x%d\n",p->addr, regs->di);
// modify one byte to make TCP checksum wrong and drop the pkt.
*((u8*)(skb->head + skb->network_header +7))=0xab;
}
return 0;
}
/* kprobe post_handler: called after the probed instruction is executed */
static void handler_post(struct kprobe *p, struct pt_regs *regs,
unsigned long flags)
{
//printk(KERN_INFO "post handler addr 0x%p skb is 0x%d\n",p->addr, regs->di);
}
/*
* fault_handler: this is called if an exception is generated for any
* instruction within the pre- or post-handler, or when Kprobes
* single-steps the probed instruction.
*/
static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
{
printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
p->addr, trapnr);
/* Return 0 because we don't handle the fault. */
return 0;
}
static int __init kprobe_init(void)
{
int ret;
kp.pre_handler = handler_pre;
kp.post_handler = handler_post;
kp.fault_handler = handler_fault;
ret = register_kprobe(&kp);
if (ret < 0) {
printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
return ret;
}
printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
return 0;
}
static void __exit kprobe_exit(void)
{
unregister_kprobe(&kp);
printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
}
module_init(kprobe_init)
module_exit(kprobe_exit)
MODULE_LICENSE("GPL");
问题已关闭。
其实在sys/kernel/debug/kprobes/list
我们可以得到注册的kprobe列表。我得到这个 xxxxxxxxxxx k ip_rcv+0x0 [FTRACE]
,这意味着这个 kprobe 是 ftrace-based。 ftrace-based 如果禁用 ftrace,kprobe 将无法工作。