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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
42static struct class *msr_class;
43static enum cpuhp_state cpuhp_msr_state;
44
45enum allow_write_msrs {
46 MSR_WRITES_ON,
47 MSR_WRITES_OFF,
48 MSR_WRITES_DEFAULT,
49};
50
51static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT;
52
53static 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
81static 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 pr_warn("Write to unrecognized MSR 0x%x by %s (pid: %d).\n",
103 reg, current->comm, current->pid);
104 pr_warn("See https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/about for details.\n");
105
106 return 0;
107}
108
109static ssize_t msr_write(struct file *file, const char __user *buf,
110 size_t count, loff_t *ppos)
111{
112 const u32 __user *tmp = (const u32 __user *)buf;
113 u32 data[2];
114 u32 reg = *ppos;
115 int cpu = iminor(file_inode(file));
116 int err = 0;
117 ssize_t bytes = 0;
118
119 err = security_locked_down(LOCKDOWN_MSR);
120 if (err)
121 return err;
122
123 err = filter_write(reg);
124 if (err)
125 return err;
126
127 if (count % 8)
128 return -EINVAL; /* Invalid chunk size */
129
130 for (; count; count -= 8) {
131 if (copy_from_user(&data, tmp, 8)) {
132 err = -EFAULT;
133 break;
134 }
135
136 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
137
138 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
139 if (err)
140 break;
141
142 tmp += 2;
143 bytes += 8;
144 }
145
146 return bytes ? bytes : err;
147}
148
149static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
150{
151 u32 __user *uregs = (u32 __user *)arg;
152 u32 regs[8];
153 int cpu = iminor(file_inode(file));
154 int err;
155
156 switch (ioc) {
157 case X86_IOC_RDMSR_REGS:
158 if (!(file->f_mode & FMODE_READ)) {
159 err = -EBADF;
160 break;
161 }
162 if (copy_from_user(®s, uregs, sizeof(regs))) {
163 err = -EFAULT;
164 break;
165 }
166 err = rdmsr_safe_regs_on_cpu(cpu, regs);
167 if (err)
168 break;
169 if (copy_to_user(uregs, ®s, sizeof(regs)))
170 err = -EFAULT;
171 break;
172
173 case X86_IOC_WRMSR_REGS:
174 if (!(file->f_mode & FMODE_WRITE)) {
175 err = -EBADF;
176 break;
177 }
178 if (copy_from_user(®s, uregs, sizeof(regs))) {
179 err = -EFAULT;
180 break;
181 }
182 err = security_locked_down(LOCKDOWN_MSR);
183 if (err)
184 break;
185
186 err = filter_write(regs[1]);
187 if (err)
188 return err;
189
190 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
191
192 err = wrmsr_safe_regs_on_cpu(cpu, regs);
193 if (err)
194 break;
195 if (copy_to_user(uregs, ®s, sizeof(regs)))
196 err = -EFAULT;
197 break;
198
199 default:
200 err = -ENOTTY;
201 break;
202 }
203
204 return err;
205}
206
207static int msr_open(struct inode *inode, struct file *file)
208{
209 unsigned int cpu = iminor(file_inode(file));
210 struct cpuinfo_x86 *c;
211
212 if (!capable(CAP_SYS_RAWIO))
213 return -EPERM;
214
215 if (cpu >= nr_cpu_ids || !cpu_online(cpu))
216 return -ENXIO; /* No such CPU */
217
218 c = &cpu_data(cpu);
219 if (!cpu_has(c, X86_FEATURE_MSR))
220 return -EIO; /* MSR not supported */
221
222 return 0;
223}
224
225/*
226 * File operations we support
227 */
228static const struct file_operations msr_fops = {
229 .owner = THIS_MODULE,
230 .llseek = no_seek_end_llseek,
231 .read = msr_read,
232 .write = msr_write,
233 .open = msr_open,
234 .unlocked_ioctl = msr_ioctl,
235 .compat_ioctl = msr_ioctl,
236};
237
238static int msr_device_create(unsigned int cpu)
239{
240 struct device *dev;
241
242 dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
243 "msr%d", cpu);
244 return PTR_ERR_OR_ZERO(dev);
245}
246
247static int msr_device_destroy(unsigned int cpu)
248{
249 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
250 return 0;
251}
252
253static char *msr_devnode(struct device *dev, umode_t *mode)
254{
255 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
256}
257
258static int __init msr_init(void)
259{
260 int err;
261
262 if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
263 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
264 return -EBUSY;
265 }
266 msr_class = class_create(THIS_MODULE, "msr");
267 if (IS_ERR(msr_class)) {
268 err = PTR_ERR(msr_class);
269 goto out_chrdev;
270 }
271 msr_class->devnode = msr_devnode;
272
273 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
274 msr_device_create, msr_device_destroy);
275 if (err < 0)
276 goto out_class;
277 cpuhp_msr_state = err;
278 return 0;
279
280out_class:
281 class_destroy(msr_class);
282out_chrdev:
283 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
284 return err;
285}
286module_init(msr_init);
287
288static void __exit msr_exit(void)
289{
290 cpuhp_remove_state(cpuhp_msr_state);
291 class_destroy(msr_class);
292 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
293}
294module_exit(msr_exit)
295
296static int set_allow_writes(const char *val, const struct kernel_param *cp)
297{
298 /* val is NUL-terminated, see kernfs_fop_write() */
299 char *s = strstrip((char *)val);
300
301 if (!strcmp(s, "on"))
302 allow_writes = MSR_WRITES_ON;
303 else if (!strcmp(s, "off"))
304 allow_writes = MSR_WRITES_OFF;
305 else
306 allow_writes = MSR_WRITES_DEFAULT;
307
308 return 0;
309}
310
311static int get_allow_writes(char *buf, const struct kernel_param *kp)
312{
313 const char *res;
314
315 switch (allow_writes) {
316 case MSR_WRITES_ON: res = "on"; break;
317 case MSR_WRITES_OFF: res = "off"; break;
318 default: res = "default"; break;
319 }
320
321 return sprintf(buf, "%s\n", res);
322}
323
324static const struct kernel_param_ops allow_writes_ops = {
325 .set = set_allow_writes,
326 .get = get_allow_writes
327};
328
329module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600);
330
331MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
332MODULE_DESCRIPTION("x86 generic MSR driver");
333MODULE_LICENSE("GPL");
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
42static struct class *msr_class;
43static enum cpuhp_state cpuhp_msr_state;
44
45enum allow_write_msrs {
46 MSR_WRITES_ON,
47 MSR_WRITES_OFF,
48 MSR_WRITES_DEFAULT,
49};
50
51static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT;
52
53static 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
81static 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
99static 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
139static 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
190static 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 */
211static 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
221static 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
230static int msr_device_destroy(unsigned int cpu)
231{
232 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
233 return 0;
234}
235
236static char *msr_devnode(struct device *dev, umode_t *mode)
237{
238 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
239}
240
241static 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
263out_class:
264 class_destroy(msr_class);
265out_chrdev:
266 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
267 return err;
268}
269module_init(msr_init);
270
271static 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}
277module_exit(msr_exit)
278
279static 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
294static 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
307static const struct kernel_param_ops allow_writes_ops = {
308 .set = set_allow_writes,
309 .get = get_allow_writes
310};
311
312module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600);
313
314MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
315MODULE_DESCRIPTION("x86 generic MSR driver");
316MODULE_LICENSE("GPL");