my_syscall.zip_my_syscall_syscall_内核模块_系统调用

#include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> #include <linux/proc_fs.h> #include <linux/sched.h> #include <linux/time.h> #include <asm/uaccess.h> #define __NR_mysyscall 2 MODULE_DESCRIPTION("my system call"); MODULE_AUTHOR("jerry"); MODULE_LICENSE("Dual BSD/GPL"); #define MODULE_NAME "mysystemcall" static int (*anything_saved)(void); static void try_write_file(const char* filename, const void* data, int len); /** * clear WP bit of CR0, and return the original value */ unsigned int clear_and_return_cr0(void) { unsigned int cr0 = 0; unsigned int ret; asm volatile ("movl %%cr0, %%eax" : "=a"(cr0) ); ret = cr0; /* clear the 20 bit of CR0, a.k.a WP bit */ cr0 &= 0xfffeffff; asm volatile ("movl %%eax, %%cr0" : : "a"(cr0) ); return ret; } /** set CR0 with new value * * @val : new value to set in cr0 */ void setback_cr0(unsigned int val) { asm volatile ("movl %%eax, %%cr0" : : "a"(val) ); } static asmlinkage int sys_mycall(int flag, struct timeval *current_time){ struct timeval temp; try_module_get(THIS_MODULE); do_gettimeofday(&temp); if(copy_to_user(current_time,&temp,sizeof(temp))){ module_put(THIS_MODULE); return -EFAULT; } if(flag){ char buffer[100]; sprintf(buffer, "Current time:\t%lds, %ldus.\n", temp.tv_sec, temp.tv_usec); try_write_file("/dev/tty", buffer, strlen(buffer)); } module_put(THIS_MODULE); return 0; } int __init init_addsyscall(void){ unsigned int returnN; returnN = clear_and_return_cr0(); long *systable; systable=(long*)0xc03868a0; anything_saved=(int(*)(void))(systable[__NR_mysyscall]); systable[__NR_mysyscall]=(unsigned long)sys_mycall; setback_cr0(returnN); return 0; } void __exit exit_addsyscall(void){ unsigned int returnN; returnN = clear_and_return_cr0(); long *systable; systable=(long*)0xc03868a0; //extern long sys_call_table[]; systable[__NR_mysyscall] = (unsigned long)anything_saved; setback_cr0(returnN); } module_init(init_addsyscall); module_exit(exit_addsyscall); void try_write_file(const char* filename, const void* data, int len){ mm_segment_t old_fs; struct file* file = filp_open(filename, O_RDONLY, 0); if(IS_ERR(file)) return; if((!file-> f_op)||(!file->f_op->write)){ filp_close(file, NULL); return; } old_fs = get_fs(); set_fs(get_ds()); file->f_op->write(file, data, len, &file->f_pos); set_fs(old_fs); }