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 enum cpuhp_state cpuhp_msr_state; 43 44 enum allow_write_msrs { 45 MSR_WRITES_ON, 46 MSR_WRITES_OFF, 47 MSR_WRITES_DEFAULT, 48 }; 49 50 static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT; 51 52 static ssize_t msr_read(struct file *file, char __user *buf, 53 size_t count, loff_t *ppos) 54 { 55 u32 __user *tmp = (u32 __user *) buf; 56 u32 data[2]; 57 u32 reg = *ppos; 58 int cpu = iminor(file_inode(file)); 59 int err = 0; 60 ssize_t bytes = 0; 61 62 if (count % 8) 63 return -EINVAL; /* Invalid chunk size */ 64 65 for (; count; count -= 8) { 66 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]); 67 if (err) 68 break; 69 if (copy_to_user(tmp, &data, 8)) { 70 err = -EFAULT; 71 break; 72 } 73 tmp += 2; 74 bytes += 8; 75 } 76 77 return bytes ? bytes : err; 78 } 79 80 static int filter_write(u32 reg) 81 { 82 /* 83 * MSRs writes usually happen all at once, and can easily saturate kmsg. 84 * Only allow one message every 30 seconds. 85 * 86 * It's possible to be smarter here and do it (for example) per-MSR, but 87 * it would certainly be more complex, and this is enough at least to 88 * avoid saturating the ring buffer. 89 */ 90 static DEFINE_RATELIMIT_STATE(fw_rs, 30 * HZ, 1); 91 92 switch (allow_writes) { 93 case MSR_WRITES_ON: return 0; 94 case MSR_WRITES_OFF: return -EPERM; 95 default: break; 96 } 97 98 if (!__ratelimit(&fw_rs)) 99 return 0; 100 101 pr_warn("Write to unrecognized MSR 0x%x by %s (pid: %d).\n", 102 reg, current->comm, current->pid); 103 pr_warn("See https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/about for details.\n"); 104 105 return 0; 106 } 107 108 static ssize_t msr_write(struct file *file, const char __user *buf, 109 size_t count, loff_t *ppos) 110 { 111 const u32 __user *tmp = (const u32 __user *)buf; 112 u32 data[2]; 113 u32 reg = *ppos; 114 int cpu = iminor(file_inode(file)); 115 int err = 0; 116 ssize_t bytes = 0; 117 118 err = security_locked_down(LOCKDOWN_MSR); 119 if (err) 120 return err; 121 122 err = filter_write(reg); 123 if (err) 124 return err; 125 126 if (count % 8) 127 return -EINVAL; /* Invalid chunk size */ 128 129 for (; count; count -= 8) { 130 if (copy_from_user(&data, tmp, 8)) { 131 err = -EFAULT; 132 break; 133 } 134 135 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK); 136 137 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]); 138 if (err) 139 break; 140 141 tmp += 2; 142 bytes += 8; 143 } 144 145 return bytes ? bytes : err; 146 } 147 148 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) 149 { 150 u32 __user *uregs = (u32 __user *)arg; 151 u32 regs[8]; 152 int cpu = iminor(file_inode(file)); 153 int err; 154 155 switch (ioc) { 156 case X86_IOC_RDMSR_REGS: 157 if (!(file->f_mode & FMODE_READ)) { 158 err = -EBADF; 159 break; 160 } 161 if (copy_from_user(®s, uregs, sizeof(regs))) { 162 err = -EFAULT; 163 break; 164 } 165 err = rdmsr_safe_regs_on_cpu(cpu, regs); 166 if (err) 167 break; 168 if (copy_to_user(uregs, ®s, sizeof(regs))) 169 err = -EFAULT; 170 break; 171 172 case X86_IOC_WRMSR_REGS: 173 if (!(file->f_mode & FMODE_WRITE)) { 174 err = -EBADF; 175 break; 176 } 177 if (copy_from_user(®s, uregs, sizeof(regs))) { 178 err = -EFAULT; 179 break; 180 } 181 err = security_locked_down(LOCKDOWN_MSR); 182 if (err) 183 break; 184 185 err = filter_write(regs[1]); 186 if (err) 187 return err; 188 189 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK); 190 191 err = wrmsr_safe_regs_on_cpu(cpu, regs); 192 if (err) 193 break; 194 if (copy_to_user(uregs, ®s, sizeof(regs))) 195 err = -EFAULT; 196 break; 197 198 default: 199 err = -ENOTTY; 200 break; 201 } 202 203 return err; 204 } 205 206 static int msr_open(struct inode *inode, struct file *file) 207 { 208 unsigned int cpu = iminor(file_inode(file)); 209 struct cpuinfo_x86 *c; 210 211 if (!capable(CAP_SYS_RAWIO)) 212 return -EPERM; 213 214 if (cpu >= nr_cpu_ids || !cpu_online(cpu)) 215 return -ENXIO; /* No such CPU */ 216 217 c = &cpu_data(cpu); 218 if (!cpu_has(c, X86_FEATURE_MSR)) 219 return -EIO; /* MSR not supported */ 220 221 return 0; 222 } 223 224 /* 225 * File operations we support 226 */ 227 static const struct file_operations msr_fops = { 228 .owner = THIS_MODULE, 229 .llseek = no_seek_end_llseek, 230 .read = msr_read, 231 .write = msr_write, 232 .open = msr_open, 233 .unlocked_ioctl = msr_ioctl, 234 .compat_ioctl = msr_ioctl, 235 }; 236 237 static char *msr_devnode(const struct device *dev, umode_t *mode) 238 { 239 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt)); 240 } 241 242 static const struct class msr_class = { 243 .name = "msr", 244 .devnode = msr_devnode, 245 }; 246 247 static int msr_device_create(unsigned int cpu) 248 { 249 struct device *dev; 250 251 dev = device_create(&msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL, 252 "msr%d", cpu); 253 return PTR_ERR_OR_ZERO(dev); 254 } 255 256 static int msr_device_destroy(unsigned int cpu) 257 { 258 device_destroy(&msr_class, MKDEV(MSR_MAJOR, cpu)); 259 return 0; 260 } 261 262 static int __init msr_init(void) 263 { 264 int err; 265 266 if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) { 267 pr_err("unable to get major %d for msr\n", MSR_MAJOR); 268 return -EBUSY; 269 } 270 err = class_register(&msr_class); 271 if (err) 272 goto out_chrdev; 273 274 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online", 275 msr_device_create, msr_device_destroy); 276 if (err < 0) 277 goto out_class; 278 cpuhp_msr_state = err; 279 return 0; 280 281 out_class: 282 class_unregister(&msr_class); 283 out_chrdev: 284 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); 285 return err; 286 } 287 module_init(msr_init); 288 289 static void __exit msr_exit(void) 290 { 291 cpuhp_remove_state(cpuhp_msr_state); 292 class_unregister(&msr_class); 293 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); 294 } 295 module_exit(msr_exit) 296 297 static int set_allow_writes(const char *val, const struct kernel_param *cp) 298 { 299 /* val is NUL-terminated, see kernfs_fop_write() */ 300 char *s = strstrip((char *)val); 301 302 if (!strcmp(s, "on")) 303 allow_writes = MSR_WRITES_ON; 304 else if (!strcmp(s, "off")) 305 allow_writes = MSR_WRITES_OFF; 306 else 307 allow_writes = MSR_WRITES_DEFAULT; 308 309 return 0; 310 } 311 312 static int get_allow_writes(char *buf, const struct kernel_param *kp) 313 { 314 const char *res; 315 316 switch (allow_writes) { 317 case MSR_WRITES_ON: res = "on"; break; 318 case MSR_WRITES_OFF: res = "off"; break; 319 default: res = "default"; break; 320 } 321 322 return sprintf(buf, "%s\n", res); 323 } 324 325 static const struct kernel_param_ops allow_writes_ops = { 326 .set = set_allow_writes, 327 .get = get_allow_writes 328 }; 329 330 module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600); 331 332 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>"); 333 MODULE_DESCRIPTION("x86 generic MSR driver"); 334 MODULE_LICENSE("GPL"); 335