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
msr_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)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
filter_write(u32 reg)81 static int filter_write(u32 reg)
82 {
83 /*
84 * MSRs writes usually happen all at once, and can easily saturate kmsg.
85 * Only allow one message every 30 seconds.
86 *
87 * It's possible to be smarter here and do it (for example) per-MSR, but
88 * it would certainly be more complex, and this is enough at least to
89 * avoid saturating the ring buffer.
90 */
91 static DEFINE_RATELIMIT_STATE(fw_rs, 30 * HZ, 1);
92
93 switch (allow_writes) {
94 case MSR_WRITES_ON: return 0;
95 case MSR_WRITES_OFF: return -EPERM;
96 default: break;
97 }
98
99 if (!__ratelimit(&fw_rs))
100 return 0;
101
102 if (reg == MSR_IA32_ENERGY_PERF_BIAS)
103 return 0;
104
105 pr_err("Write to unrecognized MSR 0x%x by %s (pid: %d). Please report to x86@kernel.org.\n",
106 reg, current->comm, current->pid);
107
108 return 0;
109 }
110
msr_write(struct file * file,const char __user * buf,size_t count,loff_t * ppos)111 static ssize_t msr_write(struct file *file, const char __user *buf,
112 size_t count, loff_t *ppos)
113 {
114 const u32 __user *tmp = (const u32 __user *)buf;
115 u32 data[2];
116 u32 reg = *ppos;
117 int cpu = iminor(file_inode(file));
118 int err = 0;
119 ssize_t bytes = 0;
120
121 err = security_locked_down(LOCKDOWN_MSR);
122 if (err)
123 return err;
124
125 err = filter_write(reg);
126 if (err)
127 return err;
128
129 if (count % 8)
130 return -EINVAL; /* Invalid chunk size */
131
132 for (; count; count -= 8) {
133 if (copy_from_user(&data, tmp, 8)) {
134 err = -EFAULT;
135 break;
136 }
137
138 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
139
140 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
141 if (err)
142 break;
143
144 tmp += 2;
145 bytes += 8;
146 }
147
148 return bytes ? bytes : err;
149 }
150
msr_ioctl(struct file * file,unsigned int ioc,unsigned long arg)151 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
152 {
153 u32 __user *uregs = (u32 __user *)arg;
154 u32 regs[8];
155 int cpu = iminor(file_inode(file));
156 int err;
157
158 switch (ioc) {
159 case X86_IOC_RDMSR_REGS:
160 if (!(file->f_mode & FMODE_READ)) {
161 err = -EBADF;
162 break;
163 }
164 if (copy_from_user(®s, uregs, sizeof(regs))) {
165 err = -EFAULT;
166 break;
167 }
168 err = rdmsr_safe_regs_on_cpu(cpu, regs);
169 if (err)
170 break;
171 if (copy_to_user(uregs, ®s, sizeof(regs)))
172 err = -EFAULT;
173 break;
174
175 case X86_IOC_WRMSR_REGS:
176 if (!(file->f_mode & FMODE_WRITE)) {
177 err = -EBADF;
178 break;
179 }
180 if (copy_from_user(®s, uregs, sizeof(regs))) {
181 err = -EFAULT;
182 break;
183 }
184 err = security_locked_down(LOCKDOWN_MSR);
185 if (err)
186 break;
187
188 err = filter_write(regs[1]);
189 if (err)
190 return err;
191
192 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
193
194 err = wrmsr_safe_regs_on_cpu(cpu, regs);
195 if (err)
196 break;
197 if (copy_to_user(uregs, ®s, sizeof(regs)))
198 err = -EFAULT;
199 break;
200
201 default:
202 err = -ENOTTY;
203 break;
204 }
205
206 return err;
207 }
208
msr_open(struct inode * inode,struct file * file)209 static int msr_open(struct inode *inode, struct file *file)
210 {
211 unsigned int cpu = iminor(file_inode(file));
212 struct cpuinfo_x86 *c;
213
214 if (!capable(CAP_SYS_RAWIO))
215 return -EPERM;
216
217 if (cpu >= nr_cpu_ids || !cpu_online(cpu))
218 return -ENXIO; /* No such CPU */
219
220 c = &cpu_data(cpu);
221 if (!cpu_has(c, X86_FEATURE_MSR))
222 return -EIO; /* MSR not supported */
223
224 return 0;
225 }
226
227 /*
228 * File operations we support
229 */
230 static const struct file_operations msr_fops = {
231 .owner = THIS_MODULE,
232 .llseek = no_seek_end_llseek,
233 .read = msr_read,
234 .write = msr_write,
235 .open = msr_open,
236 .unlocked_ioctl = msr_ioctl,
237 .compat_ioctl = msr_ioctl,
238 };
239
msr_device_create(unsigned int cpu)240 static int msr_device_create(unsigned int cpu)
241 {
242 struct device *dev;
243
244 dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
245 "msr%d", cpu);
246 return PTR_ERR_OR_ZERO(dev);
247 }
248
msr_device_destroy(unsigned int cpu)249 static int msr_device_destroy(unsigned int cpu)
250 {
251 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
252 return 0;
253 }
254
msr_devnode(struct device * dev,umode_t * mode)255 static char *msr_devnode(struct device *dev, umode_t *mode)
256 {
257 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
258 }
259
msr_init(void)260 static int __init msr_init(void)
261 {
262 int err;
263
264 if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
265 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
266 return -EBUSY;
267 }
268 msr_class = class_create(THIS_MODULE, "msr");
269 if (IS_ERR(msr_class)) {
270 err = PTR_ERR(msr_class);
271 goto out_chrdev;
272 }
273 msr_class->devnode = msr_devnode;
274
275 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
276 msr_device_create, msr_device_destroy);
277 if (err < 0)
278 goto out_class;
279 cpuhp_msr_state = err;
280 return 0;
281
282 out_class:
283 class_destroy(msr_class);
284 out_chrdev:
285 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
286 return err;
287 }
288 module_init(msr_init);
289
msr_exit(void)290 static void __exit msr_exit(void)
291 {
292 cpuhp_remove_state(cpuhp_msr_state);
293 class_destroy(msr_class);
294 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
295 }
module_exit(msr_exit)296 module_exit(msr_exit)
297
298 static int set_allow_writes(const char *val, const struct kernel_param *cp)
299 {
300 /* val is NUL-terminated, see kernfs_fop_write() */
301 char *s = strstrip((char *)val);
302
303 if (!strcmp(s, "on"))
304 allow_writes = MSR_WRITES_ON;
305 else if (!strcmp(s, "off"))
306 allow_writes = MSR_WRITES_OFF;
307 else
308 allow_writes = MSR_WRITES_DEFAULT;
309
310 return 0;
311 }
312
get_allow_writes(char * buf,const struct kernel_param * kp)313 static int get_allow_writes(char *buf, const struct kernel_param *kp)
314 {
315 const char *res;
316
317 switch (allow_writes) {
318 case MSR_WRITES_ON: res = "on"; break;
319 case MSR_WRITES_OFF: res = "off"; break;
320 default: res = "default"; break;
321 }
322
323 return sprintf(buf, "%s\n", res);
324 }
325
326 static const struct kernel_param_ops allow_writes_ops = {
327 .set = set_allow_writes,
328 .get = get_allow_writes
329 };
330
331 module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600);
332
333 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
334 MODULE_DESCRIPTION("x86 generic MSR driver");
335 MODULE_LICENSE("GPL");
336