arch/x86/kernel/msr.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* ----------------------------------------------------------------------- *
   3  *
   4  *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
   5  *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
   6  *
   7  * ----------------------------------------------------------------------- */
   8
   9 /*
  10  * x86 MSR access device
  11  *
  12  * This device is accessed by lseek() to the appropriate register number
  13  * and then read/write in chunks of 8 bytes.  A larger size means multiple
  14  * reads or writes of the same register.
  15  *
  16  * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on
  17  * an SMP box will direct the access to CPU %d.
  18  */
  19
  20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  21
  22 #include <linux/module.h>
  23
  24 #include <linux/types.h>
  25 #include <linux/errno.h>
  26 #include <linux/fcntl.h>
  27 #include <linux/init.h>
  28 #include <linux/poll.h>
  29 #include <linux/smp.h>
  30 #include <linux/major.h>
  31 #include <linux/fs.h>
  32 #include <linux/device.h>
  33 #include <linux/cpu.h>
  34 #include <linux/notifier.h>
  35 #include <linux/uaccess.h>
  36 #include <linux/gfp.h>
  37 #include <linux/security.h>
  38
  39 #include <asm/cpufeature.h>
  40 #include <asm/msr.h>
  41
  42 static struct class *msr_class;
  43 static enum cpuhp_state cpuhp_msr_state;
  44
  45 static ssize_t msr_read(struct file *file, char __user *buf,
  46                         size_t count, loff_t *ppos)
  47 {
  48         u32 __user *tmp = (u32 __user *) buf;
  49         u32 data[2];
  50         u32 reg = *ppos;
  51         int cpu = iminor(file_inode(file));
  52         int err = 0;
  53         ssize_t bytes = 0;
  54
  55         if (count % 8)
  56                 return -EINVAL; /* Invalid chunk size */
  57
  58         for (; count; count -= 8) {
  59                 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
  60                 if (err)
  61                         break;
  62                 if (copy_to_user(tmp, &data, 8)) {
  63                         err = -EFAULT;
  64                         break;
  65                 }
  66                 tmp += 2;
  67                 bytes += 8;
  68         }
  69
  70         return bytes ? bytes : err;
  71 }
  72
  73 static ssize_t msr_write(struct file *file, const char __user *buf,
  74                          size_t count, loff_t *ppos)
  75 {
  76         const u32 __user *tmp = (const u32 __user *)buf;
  77         u32 data[2];
  78         u32 reg = *ppos;
  79         int cpu = iminor(file_inode(file));
  80         int err = 0;
  81         ssize_t bytes = 0;
  82
  83         err = security_locked_down(LOCKDOWN_MSR);
  84         if (err)
  85                 return err;
  86
  87         if (count % 8)
  88                 return -EINVAL; /* Invalid chunk size */
  89
  90         for (; count; count -= 8) {
  91                 if (copy_from_user(&data, tmp, 8)) {
  92                         err = -EFAULT;
  93                         break;
  94                 }
  95                 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
  96                 if (err)
  97                         break;
  98                 tmp += 2;
  99                 bytes += 8;
 100         }
 101
 102         return bytes ? bytes : err;
 103 }
 104
 105 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 106 {
 107         u32 __user *uregs = (u32 __user *)arg;
 108         u32 regs[8];
 109         int cpu = iminor(file_inode(file));
 110         int err;
 111
 112         switch (ioc) {
 113         case X86_IOC_RDMSR_REGS:
 114                 if (!(file->f_mode & FMODE_READ)) {
 115                         err = -EBADF;
 116                         break;
 117                 }
 118                 if (copy_from_user(&regs, uregs, sizeof(regs))) {
 119                         err = -EFAULT;
 120                         break;
 121                 }
 122                 err = rdmsr_safe_regs_on_cpu(cpu, regs);
 123                 if (err)
 124                         break;
 125                 if (copy_to_user(uregs, &regs, sizeof(regs)))
 126                         err = -EFAULT;
 127                 break;
 128
 129         case X86_IOC_WRMSR_REGS:
 130                 if (!(file->f_mode & FMODE_WRITE)) {
 131                         err = -EBADF;
 132                         break;
 133                 }
 134                 if (copy_from_user(&regs, uregs, sizeof(regs))) {
 135                         err = -EFAULT;
 136                         break;
 137                 }
 138                 err = security_locked_down(LOCKDOWN_MSR);
 139                 if (err)
 140                         break;
 141                 err = wrmsr_safe_regs_on_cpu(cpu, regs);
 142                 if (err)
 143                         break;
 144                 if (copy_to_user(uregs, &regs, sizeof(regs)))
 145                         err = -EFAULT;
 146                 break;
 147
 148         default:
 149                 err = -ENOTTY;
 150                 break;
 151         }
 152
 153         return err;
 154 }
 155
 156 static int msr_open(struct inode *inode, struct file *file)
 157 {
 158         unsigned int cpu = iminor(file_inode(file));
 159         struct cpuinfo_x86 *c;
 160
 161         if (!capable(CAP_SYS_RAWIO))
 162                 return -EPERM;
 163
 164         if (cpu >= nr_cpu_ids || !cpu_online(cpu))
 165                 return -ENXIO;  /* No such CPU */
 166
 167         c = &cpu_data(cpu);
 168         if (!cpu_has(c, X86_FEATURE_MSR))
 169                 return -EIO;    /* MSR not supported */
 170
 171         return 0;
 172 }
 173
 174 /*
 175  * File operations we support
 176  */
 177 static const struct file_operations msr_fops = {
 178         .owner = THIS_MODULE,
 179         .llseek = no_seek_end_llseek,
 180         .read = msr_read,
 181         .write = msr_write,
 182         .open = msr_open,
 183         .unlocked_ioctl = msr_ioctl,
 184         .compat_ioctl = msr_ioctl,
 185 };
 186
 187 static int msr_device_create(unsigned int cpu)
 188 {
 189         struct device *dev;
 190
 191         dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
 192                             "msr%d", cpu);
 193         return PTR_ERR_OR_ZERO(dev);
 194 }
 195
 196 static int msr_device_destroy(unsigned int cpu)
 197 {
 198         device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
 199         return 0;
 200 }
 201
 202 static char *msr_devnode(struct device *dev, umode_t *mode)
 203 {
 204         return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
 205 }
 206
 207 static int __init msr_init(void)
 208 {
 209         int err;
 210
 211         if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
 212                 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
 213                 return -EBUSY;
 214         }
 215         msr_class = class_create(THIS_MODULE, "msr");
 216         if (IS_ERR(msr_class)) {
 217                 err = PTR_ERR(msr_class);
 218                 goto out_chrdev;
 219         }
 220         msr_class->devnode = msr_devnode;
 221
 222         err  = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
 223                                  msr_device_create, msr_device_destroy);
 224         if (err < 0)
 225                 goto out_class;
 226         cpuhp_msr_state = err;
 227         return 0;
 228
 229 out_class:
 230         class_destroy(msr_class);
 231 out_chrdev:
 232         __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
 233         return err;
 234 }
 235 module_init(msr_init);
 236
 237 static void __exit msr_exit(void)
 238 {
 239         cpuhp_remove_state(cpuhp_msr_state);
 240         class_destroy(msr_class);
 241         __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
 242 }
 243 module_exit(msr_exit)
 244
 245 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
 246 MODULE_DESCRIPTION("x86 generic MSR driver");
 247 MODULE_LICENSE("GPL");