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I have always been told(In books and tutorials) that while copying data from kernel space to user space, we should use copy_to_user() and using memcpy() would cause problems to the system. Recently by mistake i have used memcpy() and it worked perfectly fine with out any problems. Why is that we should use copy_to_user instead of memcpy() My test code(Kernel module) is something like this: static ssize_t test_read(struct file *file, char __user * buf, size_t len, loff_t * offset) { char ani[100]; if (!*offset) { memset(ani, 'A', 100); if (memcpy(buf, ani, 100)) return -EFAULT; *offset = 100; return *offset; } return 0; } struct file_operations test_fops = { .owner = THIS_MODULE, .read = test_read, }; static int __init my_module_init(void) { struct proc_dir_entry *entry; printk("We are testing now!!\n"); entry = create_proc_entry("test", S_IFREG | S_IRUGO, NULL); if (!entry) printk("Failed to creats proc entry test\n"); entry->proc_fops = &test_fops; return 0; } module_init(my_module_init); From user-space app, i am reading my /proc entry and everything works fine. A look at source code of copy_to_user() says that it is also simple memcpy() where we are just trying to check if the pointer is valid or not with access_ok and doing memcpy. So my understanding currently is that, if we are sure about the pointer we are passing, memcpy() can always be used in place of copy_to_user . Please correct me if my understanding is incorrect and also, any example where copy_to_user works and memcpy() fails would be very useful . Thanks.

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