arch/x86/kernel/msr.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2000-2008 H. Peter Anvin - All Rights Reserved
   4  *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
   5  *
   6  *   This program is free software; you can redistribute it and/or modify
   7  *   it under the terms of the GNU General Public License as published by
   8  *   the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
   9  *   USA; either version 2 of the License, or (at your option) any later
  10  *   version; incorporated herein by reference.
  11  *
  12  * ----------------------------------------------------------------------- */
  13
  14 /*
  15  * x86 MSR access device
  16  *
  17  * This device is accessed by lseek() to the appropriate register number
  18  * and then read/write in chunks of 8 bytes.  A larger size means multiple
  19  * reads or writes of the same register.
  20  *
  21  * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on
  22  * an SMP box will direct the access to CPU %d.
  23  */
  24
  25 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  26
  27 #include <linux/module.h>
  28
  29 #include <linux/types.h>
  30 #include <linux/errno.h>
  31 #include <linux/fcntl.h>
  32 #include <linux/init.h>
  33 #include <linux/poll.h>
  34 #include <linux/smp.h>
  35 #include <linux/major.h>
  36 #include <linux/fs.h>
  37 #include <linux/device.h>
  38 #include <linux/cpu.h>
  39 #include <linux/notifier.h>
  40 #include <linux/uaccess.h>
  41 #include <linux/gfp.h>
  42
  43 #include <asm/cpufeature.h>
  44 #include <asm/msr.h>
  45
  46 static struct class *msr_class;
  47 static enum cpuhp_state cpuhp_msr_state;
  48
  49 static ssize_t msr_read(struct file *file, char __user *buf,
  50                         size_t count, loff_t *ppos)
  51 {
  52         u32 __user *tmp = (u32 __user *) buf;
  53         u32 data[2];
  54         u32 reg = *ppos;
  55         int cpu = iminor(file_inode(file));
  56         int err = 0;
  57         ssize_t bytes = 0;
  58
  59         if (count % 8)
  60                 return -EINVAL; /* Invalid chunk size */
  61
  62         for (; count; count -= 8) {
  63                 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
  64                 if (err)
  65                         break;
  66                 if (copy_to_user(tmp, &data, 8)) {
  67                         err = -EFAULT;
  68                         break;
  69                 }
  70                 tmp += 2;
  71                 bytes += 8;
  72         }
  73
  74         return bytes ? bytes : err;
  75 }
  76
  77 static ssize_t msr_write(struct file *file, const char __user *buf,
  78                          size_t count, loff_t *ppos)
  79 {
  80         const u32 __user *tmp = (const u32 __user *)buf;
  81         u32 data[2];
  82         u32 reg = *ppos;
  83         int cpu = iminor(file_inode(file));
  84         int err = 0;
  85         ssize_t bytes = 0;
  86
  87         if (kernel_is_locked_down("Direct MSR access")) {
  88                 pr_info("Direct access to MSR %x\n", reg);
  89                 return -EPERM;
  90         }
  91
  92         if (count % 8)
  93                 return -EINVAL; /* Invalid chunk size */
  94
  95         for (; count; count -= 8) {
  96                 if (copy_from_user(&data, tmp, 8)) {
  97                         err = -EFAULT;
  98                         break;
  99                 }
 100                 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
 101                 if (err)
 102                         break;
 103                 tmp += 2;
 104                 bytes += 8;
 105         }
 106
 107         return bytes ? bytes : err;
 108 }
 109
 110 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 111 {
 112         u32 __user *uregs = (u32 __user *)arg;
 113         u32 regs[8];
 114         int cpu = iminor(file_inode(file));
 115         int err;
 116
 117         switch (ioc) {
 118         case X86_IOC_RDMSR_REGS:
 119                 if (!(file->f_mode & FMODE_READ)) {
 120                         err = -EBADF;
 121                         break;
 122                 }
 123                 if (copy_from_user(&regs, uregs, sizeof regs)) {
 124                         err = -EFAULT;
 125                         break;
 126                 }
 127                 err = rdmsr_safe_regs_on_cpu(cpu, regs);
 128                 if (err)
 129                         break;
 130                 if (copy_to_user(uregs, &regs, sizeof regs))
 131                         err = -EFAULT;
 132                 break;
 133
 134         case X86_IOC_WRMSR_REGS:
 135                 if (!(file->f_mode & FMODE_WRITE)) {
 136                         err = -EBADF;
 137                         break;
 138                 }
 139                 if (copy_from_user(&regs, uregs, sizeof regs)) {
 140                         err = -EFAULT;
 141                         break;
 142                 }
 143                 if (kernel_is_locked_down("Direct MSR access")) {
 144                         pr_info("Direct access to MSR %x\n", regs[1]); /* Display %ecx */
 145                         err = -EPERM;
 146                         break;
 147                 }
 148                 err = wrmsr_safe_regs_on_cpu(cpu, regs);
 149                 if (err)
 150                         break;
 151                 if (copy_to_user(uregs, &regs, sizeof regs))
 152                         err = -EFAULT;
 153                 break;
 154
 155         default:
 156                 err = -ENOTTY;
 157                 break;
 158         }
 159
 160         return err;
 161 }
 162
 163 static int msr_open(struct inode *inode, struct file *file)
 164 {
 165         unsigned int cpu = iminor(file_inode(file));
 166         struct cpuinfo_x86 *c;
 167
 168         if (!capable(CAP_SYS_RAWIO))
 169                 return -EPERM;
 170
 171         if (cpu >= nr_cpu_ids || !cpu_online(cpu))
 172                 return -ENXIO;  /* No such CPU */
 173
 174         c = &cpu_data(cpu);
 175         if (!cpu_has(c, X86_FEATURE_MSR))
 176                 return -EIO;    /* MSR not supported */
 177
 178         return 0;
 179 }
 180
 181 /*
 182  * File operations we support
 183  */
 184 static const struct file_operations msr_fops = {
 185         .owner = THIS_MODULE,
 186         .llseek = no_seek_end_llseek,
 187         .read = msr_read,
 188         .write = msr_write,
 189         .open = msr_open,
 190         .unlocked_ioctl = msr_ioctl,
 191         .compat_ioctl = msr_ioctl,
 192 };
 193
 194 static int msr_device_create(unsigned int cpu)
 195 {
 196         struct device *dev;
 197
 198         dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
 199                             "msr%d", cpu);
 200         return PTR_ERR_OR_ZERO(dev);
 201 }
 202
 203 static int msr_device_destroy(unsigned int cpu)
 204 {
 205         device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
 206         return 0;
 207 }
 208
 209 static char *msr_devnode(struct device *dev, umode_t *mode)
 210 {
 211         return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
 212 }
 213
 214 static int __init msr_init(void)
 215 {
 216         int err;
 217
 218         if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
 219                 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
 220                 return -EBUSY;
 221         }
 222         msr_class = class_create(THIS_MODULE, "msr");
 223         if (IS_ERR(msr_class)) {
 224                 err = PTR_ERR(msr_class);
 225                 goto out_chrdev;
 226         }
 227         msr_class->devnode = msr_devnode;
 228
 229         err  = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
 230                                  msr_device_create, msr_device_destroy);
 231         if (err < 0)
 232                 goto out_class;
 233         cpuhp_msr_state = err;
 234         return 0;
 235
 236 out_class:
 237         class_destroy(msr_class);
 238 out_chrdev:
 239         __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
 240         return err;
 241 }
 242 module_init(msr_init);
 243
 244 static void __exit msr_exit(void)
 245 {
 246         cpuhp_remove_state(cpuhp_msr_state);
 247         class_destroy(msr_class);
 248         __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
 249 }
 250 module_exit(msr_exit)
 251
 252 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
 253 MODULE_DESCRIPTION("x86 generic MSR driver");
 254 MODULE_LICENSE("GPL");