Continuing Linux Kernel Development - My second Linux Kernel Module (LKM) - Adding parameters

In the previous post, I had a basic module without any parameters. In this second post, I have modified the code in the previous post to accommodate parameters.

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/* * This is my second crack at writing a Linux Kernel Module (LKM) * This file accommodates parameters * Author: Nik Alleyne * Blog: www.securitynik.com * File: helloWorld-parmameters.c */ // init.h needed for entry and exit macros #include <linux/init.h> // Remember every module needs module linux/module.h #include <linux/module.h> // kernel.h is needed for printk() in this example #include <linux/kernel.h> #include <asm/current.h> // Specify the license information. License choice impacts the way the kernel treats your module. MODULE_LICENSE("GPL v2"); MODULE_AUTHOR("Nik Alleyne - www.securitynik.com"); MODULE_DESCRIPTION("My Second shot at Kernel Module (LKM) \n\t\tRequires 2 parameters: name and count"); MODULE_VERSION("0.2"); MODULE_ALIAS("SecurityNik Hello World with parameters"); /* * Here is where this program differs from the one in the previous post * Below represents the declaration of the arguments via the module_param() macro * S_IRUGO permission allows the parameter to be read by the world but not changed */ // Setup for the name parameter static char *fname = "SecurityNik"; module_param(fname, charp, S_IRUGO); MODULE_PARM_DESC(fname, " Specify a fist name for the user"); static char *lname = "SecurityNik"; module_param(lname, charp, S_IRUGO); MODULE_PARM_DESC(lname, " Specify a last name for the user"); // Setup the initialization module. Basically what the LKM does at startup static int __init hello_init(void) { printk(KERN_INFO "[*] WELCOME!! '%s %s' to SecurityNik LKM World! \n Enjoy your stay!", fname, lname); printk(KERN_INFO "[*] The current process is [%s] with PID[%i]\n", current->comm, current->pid); // Always return 0 to show success. // If a non-zero value is returned it more than likely means an error occurred while loading return 0; } // Setup the cleanup module. Basically what the LKM does upon exit static void __exit hello_exit(void) { printk(KERN_INFO "[*] THANK YOU!! '%s %s' for visiting. See ya ...\n", fname, lname); } // Now tell the system which module to load upon initialization module_init(hello_init); // Which module to call upon exit module_exit(hello_exit); /* * References: * https://elixir.bootlin.com/linux/latest/source/include/linux/module.h * https://elixir.bootlin.com/linux/latest/source/include/linux/kernel.h * https://elixir.bootlin.com/linux/latest/source/include/linux/printk.h * https://elixir.bootlin.com/linux/latest/source/include/linux/tty.h * http://www.makelinux.net/ldd3/chp-2-sect-8.shtml */

Perform the make similar to what was done before and created the following files:

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kali@securitynik:~/rootkits/HelloWorld2$ make all make --directory=/lib/modules/5.5.0-kali2-amd64/build/ M=/home/kali/rootkits/HelloWorld2 modules make[1]: Entering directory '/usr/src/linux-headers-5.5.0-kali2-amd64' CC [M] /home/kali/rootkits/HelloWorld2/helloWorld-parmameters.o Building modules, stage 2. MODPOST 1 modules CC [M] /home/kali/rootkits/HelloWorld2/helloWorld-parmameters.mod.o LD [M] /home/kali/rootkits/HelloWorld2/helloWorld-parmameters.ko make[1]: Leaving directory '/usr/src/linux-headers-5.5.0-kali2-amd64'

Peeking into the module before installing it and we see the two parameters below in the last two lines.

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kali@securitynik:~/rootkits/HelloWorld2$ sudo modinfo helloWorld-parmameters.ko filename: /home/kali/rootkits/HelloWorld2/helloWorld-parmameters.ko alias: SecurityNik Hello World with parameters version: 0.2 description: My Second shot at Kernel Module (LKM) Requires 2 parameters: name and count author: Nik Alleyne - www.securitynik.com license: GPL v2 srcversion: 49300DF20231CF765D9471F depends: retpoline: Y name: helloWorld_parmameters vermagic: 5.5.0-kali2-amd64 SMP mod_unload modversions parm: fname: Specify a fist name for the user (charp) parm: lname: Specify a last name for the user (charp)

Now I install the module, using the two parameters.

1	kali@securitynik:~/rootkits/HelloWorld2$ sudo insmod helloWorld-parmameters.ko fname="Nik" lname="Alleyne"

Let's confirm the module was installed

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kali@securitynik:~/rootkits/HelloWorld2$ sudo lsmod Module Size Used by helloWorld_parmameters 16384 0 tcp_diag 16384 0 inet_diag 20480 1 tcp_diag ....

Let's now uninstall the module

1	kali@securitynik:~/rootkits/HelloWorld2$ sudo rmmod helloWorld_parmameters

Let's now confirm the first and last name was successfully written via "dmesg --ctime".

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[Sun Jul 5 21:50:10 2020] [*] WELCOME!! 'Nik Alleyne' to SecurityNik LKM World! Enjoy your stay! [Sun Jul 5 21:50:10 2020] [*] The current process is [insmod] with PID[34871] [Sun Jul 5 21:53:22 2020] [*] THANK YOU!! 'Nik Alleyne' for visiting. See ya ...

Looks good and looks like I am making progress. Join me in the next post where I learn a bit more about processes.