如何替换内核 5.10.x 模块驱动程序版本的 set_fs(KERNEL_DS)

Question

我一直在将自定义模块驱动程序更新到 5.10.x Linux 内核版本。我的驱动程序在 cdc-acm 设备上添加了一层。为了复制该行为，使用下一个小驱动程序。

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/tty.h>
#include <linux/version.h>
#include <linux/uaccess.h>



/* Device major umber */
static int major;

/* ttyACM file descriptor */
static struct file *fd;


/* Private functions ---------------------------------------------------------*/
static int usbox_serial_baudrate_set(struct file *fd)
{
    int ret;
    mm_segment_t old_fs;
    struct termios newtio;
    //struct termios __user newtio;
    //void __user *unewtio = (void __user *) &newtio;

    memset(&newtio, 0, sizeof(newtio));
    newtio.c_cflag = (B115200 | CS8 | CLOCAL | CREAD);

#if LINUX_VERSION_CODE < KERNEL_VERSION(5,0,0)
    old_fs = get_fs();
    set_fs( get_ds() );
#elif LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
    old_fs = get_fs();
    set_fs( KERNEL_DS );
#else
    old_fs = force_uaccess_begin();
#endif

    if (fd->f_op->unlocked_ioctl) {
        ret = fd->f_op->unlocked_ioctl(fd, TCSETS, (unsigned long int) &newtio);
        pr_info("_unlocked_ioctl: %d\n", ret);
    } else {
        ret = -ENOTTY;
    }

#if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
    set_fs(old_fs);
#else
    force_uaccess_end(old_fs);
#endif

    pr_info("ret: %d\n", ret );
    return ret;
}


/* Driver Methods ------------------------------------------------------------*/
static ssize_t testdrv_read(struct file *filp,
               char __user *buf, size_t count, loff_t *ppos)
{
    return 0;
}

static ssize_t testdrv_write(struct file *filp,
                const char __user *buf, size_t count, loff_t *ppos)
{
    return 0;
}

static int testdrv_open(struct inode *inode, struct file *filp)
{
    pr_info("testdrv_open\n");

    fd = filp_open( "/dev/ttyACM0", O_RDWR|O_NOCTTY, 0);
    if (IS_ERR(fd)) {
        pr_info("error from filp_open()\n");
        return -ENODEV;
    }

    pr_info ("fd      : %p\n", fd);
    pr_info ("fd->f_op: %p\n", fd->f_op);
    pr_info ("ioctl   : %p\n", fd->f_op->unlocked_ioctl);

    if ((fd->f_op == NULL) || (fd->f_op->unlocked_ioctl == NULL)) {
        pr_info("errno: ENODEV\n");
        return -ENODEV;
    }

    // Set baudrate.
    if (usbox_serial_baudrate_set(fd) != 0 ) {
        filp_close(fd, NULL);
        pr_info("errno: EINVAL\n");
        return -EINVAL;
    }

    return 0;
}

static int testdrv_release(struct inode *inode, struct file *filp)
{
    pr_info("testdrv_release\n");

    if (fd != NULL) {
        filp_close(fd, NULL);
        fd = NULL;
    }

    return 0;
}

static struct file_operations testdrv_fops = {
    .owner      = THIS_MODULE,
    .read       = testdrv_read,
    .write      = testdrv_write,
    .open       = testdrv_open,
    .release    = testdrv_release
};


/* Module stuff --------------------------------------------------------------*/

static int __init testdrv_init(void)
{
    int ret;

    ret = register_chrdev(0, "testdrv", &testdrv_fops);
    if (ret < 0) {
        pr_err("Error %d\n", ret);
        return ret;
    }
    major = ret;
    fd = NULL;
    pr_info("Major %d\n", major);

    return 0;
}

static void __exit testdrv_exit(void)
{
    unregister_chrdev(major, "testdrv");
}

module_init(testdrv_init);
module_exit(testdrv_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Unknonw");
MODULE_DESCRIPTION("testdrv");

这里，当testdrv打开时，驱动会打开ttyACM相关。然后它调用“usbox_serial_baudrate_set”来设置波特率。该函数从填充描述符中调用“unlocked_ioctl”。为了能够使用这个电话，我必须使用

#if LINUX_VERSION_CODE < KERNEL_VERSION(5,0,0)
    old_fs = get_fs();
    set_fs( get_ds() );
#elif LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
    old_fs = get_fs();
    set_fs( KERNEL_DS );
#else
    old_fs = force_uaccess_begin();
#endif
...
        ret = fd->f_op->unlocked_ioctl(fd, TCSETS, (unsigned long int) &newtio);
...
#if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
    set_fs(old_fs);
#else
    force_uaccess_end(old_fs);
#endif

在 5.10.x 之前，此代码可以正常工作。我必须使用 KERNEL_DS 对 5.4.x 进行一些小的更改，但现在我总是从“unlocked_ioctl”中得到 EFAULT。我尝试删除“force_uaccess_begin/force_uaccess_end”但没有成功。 'unlocked_ioctl' 最终调用 /drivers/tty/tty_ioctl.c 'set_termios' 函数，但失败：

#ifdef TCGETS2
    } else if (opt & TERMIOS_OLD) {
        if (user_termios_to_kernel_termios_1(&tmp_termios,
                        (struct termios __user *)arg))
            return -EFAULT;
    } else {

函数“user_termios_to_kernel_termios_1”是一个宏

#define user_termios_to_kernel_termios_1(k, u) copy_from_user(k, u, sizeof(struct termios))

使用 4.15.0 内核，插入模块并查找相关设备后，我会在 dmesg 中收到下一条消息：

[370099.242677] testdrv:testdrv_init: Major 237
[370103.032357] testdrv:testdrv_open: testdrv_open
[370103.032635] testdrv:testdrv_open: fd      : 0000000034db75d4
[370103.032637] testdrv:testdrv_open: fd->f_op: 00000000c761e065
[370103.032638] testdrv:testdrv_open: ioctl   : 00000000608ed60c
[370103.032643] testdrv:usbox_serial_baudrate_set: _unlocked_ioctl: 0
[370103.032645] testdrv:usbox_serial_baudrate_set: ret: 0
[370103.032685] testdrv:testdrv_release: testdrv_release

并使用 5.10.1

[  294.418308] testdrv:testdrv_init: got major 244
[  296.574583] testdrv:testdrv_open: testdrv_open
[  296.575949] testdrv:testdrv_open: fd      : 00000000c35e59c0
[  296.575955] testdrv:testdrv_open: fd->f_op: 0000000041840a0e
[  296.575957] testdrv:testdrv_open: ioctl   : 000000005e21689c
[  296.575965] testdrv:usbox_serial_baudrate_set: _unlocked_ioctl: -14
[  296.575967] testdrv:usbox_serial_baudrate_set: ret: -14
[  296.575970] testdrv:testdrv_open: errno: EINVAL

任何人都可以帮助我了解发生了什么事吗？混合用户空间/内核空间数据有问题吗？我该如何解决？

Answer 1

您可以使用 CONFIG_SET_FS=y (uaccess.h) 构建内核。至少应该是 5.10 的选项。