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v5.4
  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
 
 
 
 
 
 
 
 
 45static ssize_t msr_read(struct file *file, char __user *buf,
 46			size_t count, loff_t *ppos)
 47{
 48	u32 __user *tmp = (u32 __user *) buf;
 49	u32 data[2];
 50	u32 reg = *ppos;
 51	int cpu = iminor(file_inode(file));
 52	int err = 0;
 53	ssize_t bytes = 0;
 54
 55	if (count % 8)
 56		return -EINVAL;	/* Invalid chunk size */
 57
 58	for (; count; count -= 8) {
 59		err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
 60		if (err)
 61			break;
 62		if (copy_to_user(tmp, &data, 8)) {
 63			err = -EFAULT;
 64			break;
 65		}
 66		tmp += 2;
 67		bytes += 8;
 68	}
 69
 70	return bytes ? bytes : err;
 71}
 72
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 73static ssize_t msr_write(struct file *file, const char __user *buf,
 74			 size_t count, loff_t *ppos)
 75{
 76	const u32 __user *tmp = (const u32 __user *)buf;
 77	u32 data[2];
 78	u32 reg = *ppos;
 79	int cpu = iminor(file_inode(file));
 80	int err = 0;
 81	ssize_t bytes = 0;
 82
 83	err = security_locked_down(LOCKDOWN_MSR);
 84	if (err)
 85		return err;
 86
 
 
 
 
 87	if (count % 8)
 88		return -EINVAL;	/* Invalid chunk size */
 89
 90	for (; count; count -= 8) {
 91		if (copy_from_user(&data, tmp, 8)) {
 92			err = -EFAULT;
 93			break;
 94		}
 
 
 
 95		err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
 96		if (err)
 97			break;
 
 98		tmp += 2;
 99		bytes += 8;
100	}
101
102	return bytes ? bytes : err;
103}
104
105static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
106{
107	u32 __user *uregs = (u32 __user *)arg;
108	u32 regs[8];
109	int cpu = iminor(file_inode(file));
110	int err;
111
112	switch (ioc) {
113	case X86_IOC_RDMSR_REGS:
114		if (!(file->f_mode & FMODE_READ)) {
115			err = -EBADF;
116			break;
117		}
118		if (copy_from_user(&regs, uregs, sizeof(regs))) {
119			err = -EFAULT;
120			break;
121		}
122		err = rdmsr_safe_regs_on_cpu(cpu, regs);
123		if (err)
124			break;
125		if (copy_to_user(uregs, &regs, sizeof(regs)))
126			err = -EFAULT;
127		break;
128
129	case X86_IOC_WRMSR_REGS:
130		if (!(file->f_mode & FMODE_WRITE)) {
131			err = -EBADF;
132			break;
133		}
134		if (copy_from_user(&regs, uregs, sizeof(regs))) {
135			err = -EFAULT;
136			break;
137		}
138		err = security_locked_down(LOCKDOWN_MSR);
139		if (err)
140			break;
141		err = wrmsr_safe_regs_on_cpu(cpu, regs);
142		if (err)
143			break;
144		if (copy_to_user(uregs, &regs, sizeof(regs)))
145			err = -EFAULT;
146		break;
147
148	default:
149		err = -ENOTTY;
150		break;
151	}
152
153	return err;
154}
155
156static int msr_open(struct inode *inode, struct file *file)
157{
158	unsigned int cpu = iminor(file_inode(file));
159	struct cpuinfo_x86 *c;
160
161	if (!capable(CAP_SYS_RAWIO))
162		return -EPERM;
163
164	if (cpu >= nr_cpu_ids || !cpu_online(cpu))
165		return -ENXIO;	/* No such CPU */
166
167	c = &cpu_data(cpu);
168	if (!cpu_has(c, X86_FEATURE_MSR))
169		return -EIO;	/* MSR not supported */
170
171	return 0;
172}
173
174/*
175 * File operations we support
176 */
177static const struct file_operations msr_fops = {
178	.owner = THIS_MODULE,
179	.llseek = no_seek_end_llseek,
180	.read = msr_read,
181	.write = msr_write,
182	.open = msr_open,
183	.unlocked_ioctl = msr_ioctl,
184	.compat_ioctl = msr_ioctl,
185};
186
187static int msr_device_create(unsigned int cpu)
188{
189	struct device *dev;
190
191	dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
192			    "msr%d", cpu);
193	return PTR_ERR_OR_ZERO(dev);
194}
195
196static int msr_device_destroy(unsigned int cpu)
197{
198	device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
199	return 0;
200}
201
202static char *msr_devnode(struct device *dev, umode_t *mode)
203{
204	return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
205}
206
207static int __init msr_init(void)
208{
209	int err;
210
211	if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
212		pr_err("unable to get major %d for msr\n", MSR_MAJOR);
213		return -EBUSY;
214	}
215	msr_class = class_create(THIS_MODULE, "msr");
216	if (IS_ERR(msr_class)) {
217		err = PTR_ERR(msr_class);
218		goto out_chrdev;
219	}
220	msr_class->devnode = msr_devnode;
221
222	err  = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
223				 msr_device_create, msr_device_destroy);
224	if (err < 0)
225		goto out_class;
226	cpuhp_msr_state = err;
227	return 0;
228
229out_class:
230	class_destroy(msr_class);
231out_chrdev:
232	__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
233	return err;
234}
235module_init(msr_init);
236
237static void __exit msr_exit(void)
238{
239	cpuhp_remove_state(cpuhp_msr_state);
240	class_destroy(msr_class);
241	__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
242}
243module_exit(msr_exit)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
244
245MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
246MODULE_DESCRIPTION("x86 generic MSR driver");
247MODULE_LICENSE("GPL");
v5.9
  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(&regs, 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, &regs, 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(&regs, 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, &regs, 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");