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 enum allow_write_msrs { 46 MSR_WRITES_ON, 47 MSR_WRITES_OFF, 48 MSR_WRITES_DEFAULT, 49 }; 50 51 static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT; 52 53 static ssize_t msr_read(struct file *file, char __user *buf, 54 size_t count, loff_t *ppos) 55 { 56 u32 __user *tmp = (u32 __user *) buf; 57 u32 data[2]; 58 u32 reg = *ppos; 59 int cpu = iminor(file_inode(file)); 60 int err = 0; 61 ssize_t bytes = 0; 62 63 if (count % 8) 64 return -EINVAL; /* Invalid chunk size */ 65 66 for (; count; count -= 8) { 67 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]); 68 if (err) 69 break; 70 if (copy_to_user(tmp, &data, 8)) { 71 err = -EFAULT; 72 break; 73 } 74 tmp += 2; 75 bytes += 8; 76 } 77 78 return bytes ? bytes : err; 79 } 80 81 static int filter_write(u32 reg) 82 { 83 switch (allow_writes) { 84 case MSR_WRITES_ON: return 0; 85 case MSR_WRITES_OFF: return -EPERM; 86 default: break; 87 } 88 89 if (reg == MSR_IA32_ENERGY_PERF_BIAS) 90 return 0; 91 92 pr_err_ratelimited("Write to unrecognized MSR 0x%x by %s\n" 93 "Please report to x86@kernel.org\n", 94 reg, current->comm); 95 96 return 0; 97 } 98 99 static ssize_t msr_write(struct file *file, const char __user *buf, 100 size_t count, loff_t *ppos) 101 { 102 const u32 __user *tmp = (const u32 __user *)buf; 103 u32 data[2]; 104 u32 reg = *ppos; 105 int cpu = iminor(file_inode(file)); 106 int err = 0; 107 ssize_t bytes = 0; 108 109 err = security_locked_down(LOCKDOWN_MSR); 110 if (err) 111 return err; 112 113 err = filter_write(reg); 114 if (err) 115 return err; 116 117 if (count % 8) 118 return -EINVAL; /* Invalid chunk size */ 119 120 for (; count; count -= 8) { 121 if (copy_from_user(&data, tmp, 8)) { 122 err = -EFAULT; 123 break; 124 } 125 126 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK); 127 128 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]); 129 if (err) 130 break; 131 132 tmp += 2; 133 bytes += 8; 134 } 135 136 return bytes ? bytes : err; 137 } 138 139 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) 140 { 141 u32 __user *uregs = (u32 __user *)arg; 142 u32 regs[8]; 143 int cpu = iminor(file_inode(file)); 144 int err; 145 146 switch (ioc) { 147 case X86_IOC_RDMSR_REGS: 148 if (!(file->f_mode & FMODE_READ)) { 149 err = -EBADF; 150 break; 151 } 152 if (copy_from_user(®s, uregs, sizeof(regs))) { 153 err = -EFAULT; 154 break; 155 } 156 err = rdmsr_safe_regs_on_cpu(cpu, regs); 157 if (err) 158 break; 159 if (copy_to_user(uregs, ®s, sizeof(regs))) 160 err = -EFAULT; 161 break; 162 163 case X86_IOC_WRMSR_REGS: 164 if (!(file->f_mode & FMODE_WRITE)) { 165 err = -EBADF; 166 break; 167 } 168 if (copy_from_user(®s, uregs, sizeof(regs))) { 169 err = -EFAULT; 170 break; 171 } 172 err = security_locked_down(LOCKDOWN_MSR); 173 if (err) 174 break; 175 err = wrmsr_safe_regs_on_cpu(cpu, regs); 176 if (err) 177 break; 178 if (copy_to_user(uregs, ®s, sizeof(regs))) 179 err = -EFAULT; 180 break; 181 182 default: 183 err = -ENOTTY; 184 break; 185 } 186 187 return err; 188 } 189 190 static int msr_open(struct inode *inode, struct file *file) 191 { 192 unsigned int cpu = iminor(file_inode(file)); 193 struct cpuinfo_x86 *c; 194 195 if (!capable(CAP_SYS_RAWIO)) 196 return -EPERM; 197 198 if (cpu >= nr_cpu_ids || !cpu_online(cpu)) 199 return -ENXIO; /* No such CPU */ 200 201 c = &cpu_data(cpu); 202 if (!cpu_has(c, X86_FEATURE_MSR)) 203 return -EIO; /* MSR not supported */ 204 205 return 0; 206 } 207 208 /* 209 * File operations we support 210 */ 211 static const struct file_operations msr_fops = { 212 .owner = THIS_MODULE, 213 .llseek = no_seek_end_llseek, 214 .read = msr_read, 215 .write = msr_write, 216 .open = msr_open, 217 .unlocked_ioctl = msr_ioctl, 218 .compat_ioctl = msr_ioctl, 219 }; 220 221 static int msr_device_create(unsigned int cpu) 222 { 223 struct device *dev; 224 225 dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL, 226 "msr%d", cpu); 227 return PTR_ERR_OR_ZERO(dev); 228 } 229 230 static int msr_device_destroy(unsigned int cpu) 231 { 232 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu)); 233 return 0; 234 } 235 236 static char *msr_devnode(struct device *dev, umode_t *mode) 237 { 238 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt)); 239 } 240 241 static int __init msr_init(void) 242 { 243 int err; 244 245 if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) { 246 pr_err("unable to get major %d for msr\n", MSR_MAJOR); 247 return -EBUSY; 248 } 249 msr_class = class_create(THIS_MODULE, "msr"); 250 if (IS_ERR(msr_class)) { 251 err = PTR_ERR(msr_class); 252 goto out_chrdev; 253 } 254 msr_class->devnode = msr_devnode; 255 256 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online", 257 msr_device_create, msr_device_destroy); 258 if (err < 0) 259 goto out_class; 260 cpuhp_msr_state = err; 261 return 0; 262 263 out_class: 264 class_destroy(msr_class); 265 out_chrdev: 266 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); 267 return err; 268 } 269 module_init(msr_init); 270 271 static void __exit msr_exit(void) 272 { 273 cpuhp_remove_state(cpuhp_msr_state); 274 class_destroy(msr_class); 275 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); 276 } 277 module_exit(msr_exit) 278 279 static int set_allow_writes(const char *val, const struct kernel_param *cp) 280 { 281 /* val is NUL-terminated, see kernfs_fop_write() */ 282 char *s = strstrip((char *)val); 283 284 if (!strcmp(s, "on")) 285 allow_writes = MSR_WRITES_ON; 286 else if (!strcmp(s, "off")) 287 allow_writes = MSR_WRITES_OFF; 288 else 289 allow_writes = MSR_WRITES_DEFAULT; 290 291 return 0; 292 } 293 294 static int get_allow_writes(char *buf, const struct kernel_param *kp) 295 { 296 const char *res; 297 298 switch (allow_writes) { 299 case MSR_WRITES_ON: res = "on"; break; 300 case MSR_WRITES_OFF: res = "off"; break; 301 default: res = "default"; break; 302 } 303 304 return sprintf(buf, "%s\n", res); 305 } 306 307 static const struct kernel_param_ops allow_writes_ops = { 308 .set = set_allow_writes, 309 .get = get_allow_writes 310 }; 311 312 module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600); 313 314 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>"); 315 MODULE_DESCRIPTION("x86 generic MSR driver"); 316 MODULE_LICENSE("GPL"); 317