[PATCH] Implement uhook(call kernel func from userspace) driver

[Peiyong Feng]

Hi all,

This patch implement the uhook kernel driver. Here are some ideals and
explanations:

1. What is uhook

uhook(userspace kernel hook) means call kernel function from
userspace. That is to say, we can

write a function in kernel space and call it in userspace while the
kernel Image is running. For example:


I write  a function in kernel, like following:

+int uhook_unlock(void)
+{
+       printk(KERN_INFO"Unlock mutex\n");
+       mutex_unlock(&uhook_global->mutex);
+       return -1;
+}
+EXPORT_SYMBOL_GPL(uhook_test);

I can call it from userspace using uhook application:

uhook --type run uhook_test


2. What we can do with uhook

The most exciting feature of uhook is that we call kernel function in
userspace while kernel is running.
So,

A. We can using uhook to dump value of kernel argument when some thing
goes wrong. Especially when
the device driver cannot work correctly, we can dump some device
registers to examine what is going on.

B. We can implement some switch in kernel to control if branch. For example:

if (branch_control) {
     balabalabala......
     .....
}

We can dynamic change the value of branch_control to let kernel run
the specific code or not.

C. Whatever you want kernel do.



3. Compare to /proc or /sys file system

Kernel has some component like /proc and /sys file system to perform
the communication between kernel
and user space. But they are so complex that we must write some code
very time we want to use them. However,
with uhook, we just need to insmod the uhook.ko, then call the kernel
function whenever and wherever.


4. TODO

A. This version of uhook, can just support kernel function prototype
like int func(void). I donot know how to deal
with the function that has many argument and variable return type.

B. The user space applicantion: uhook, is just a test, so poor, cannot
process complex command option, I am still
working on it



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