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0020 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0021
0022 #include <linux/module.h>
0023
0024 #include <linux/types.h>
0025 #include <linux/errno.h>
0026 #include <linux/fcntl.h>
0027 #include <linux/init.h>
0028 #include <linux/poll.h>
0029 #include <linux/smp.h>
0030 #include <linux/major.h>
0031 #include <linux/fs.h>
0032 #include <linux/device.h>
0033 #include <linux/cpu.h>
0034 #include <linux/notifier.h>
0035 #include <linux/uaccess.h>
0036 #include <linux/gfp.h>
0037 #include <linux/security.h>
0038
0039 #include <asm/cpufeature.h>
0040 #include <asm/msr.h>
0041
0042 static struct class *msr_class;
0043 static enum cpuhp_state cpuhp_msr_state;
0044
0045 enum allow_write_msrs {
0046 MSR_WRITES_ON,
0047 MSR_WRITES_OFF,
0048 MSR_WRITES_DEFAULT,
0049 };
0050
0051 static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT;
0052
0053 static ssize_t msr_read(struct file *file, char __user *buf,
0054 size_t count, loff_t *ppos)
0055 {
0056 u32 __user *tmp = (u32 __user *) buf;
0057 u32 data[2];
0058 u32 reg = *ppos;
0059 int cpu = iminor(file_inode(file));
0060 int err = 0;
0061 ssize_t bytes = 0;
0062
0063 if (count % 8)
0064 return -EINVAL;
0065
0066 for (; count; count -= 8) {
0067 err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
0068 if (err)
0069 break;
0070 if (copy_to_user(tmp, &data, 8)) {
0071 err = -EFAULT;
0072 break;
0073 }
0074 tmp += 2;
0075 bytes += 8;
0076 }
0077
0078 return bytes ? bytes : err;
0079 }
0080
0081 static int filter_write(u32 reg)
0082 {
0083
0084
0085
0086
0087
0088
0089
0090
0091 static DEFINE_RATELIMIT_STATE(fw_rs, 30 * HZ, 1);
0092
0093 switch (allow_writes) {
0094 case MSR_WRITES_ON: return 0;
0095 case MSR_WRITES_OFF: return -EPERM;
0096 default: break;
0097 }
0098
0099 if (!__ratelimit(&fw_rs))
0100 return 0;
0101
0102 pr_warn("Write to unrecognized MSR 0x%x by %s (pid: %d).\n",
0103 reg, current->comm, current->pid);
0104 pr_warn("See https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/about for details.\n");
0105
0106 return 0;
0107 }
0108
0109 static ssize_t msr_write(struct file *file, const char __user *buf,
0110 size_t count, loff_t *ppos)
0111 {
0112 const u32 __user *tmp = (const u32 __user *)buf;
0113 u32 data[2];
0114 u32 reg = *ppos;
0115 int cpu = iminor(file_inode(file));
0116 int err = 0;
0117 ssize_t bytes = 0;
0118
0119 err = security_locked_down(LOCKDOWN_MSR);
0120 if (err)
0121 return err;
0122
0123 err = filter_write(reg);
0124 if (err)
0125 return err;
0126
0127 if (count % 8)
0128 return -EINVAL;
0129
0130 for (; count; count -= 8) {
0131 if (copy_from_user(&data, tmp, 8)) {
0132 err = -EFAULT;
0133 break;
0134 }
0135
0136 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
0137
0138 err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
0139 if (err)
0140 break;
0141
0142 tmp += 2;
0143 bytes += 8;
0144 }
0145
0146 return bytes ? bytes : err;
0147 }
0148
0149 static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
0150 {
0151 u32 __user *uregs = (u32 __user *)arg;
0152 u32 regs[8];
0153 int cpu = iminor(file_inode(file));
0154 int err;
0155
0156 switch (ioc) {
0157 case X86_IOC_RDMSR_REGS:
0158 if (!(file->f_mode & FMODE_READ)) {
0159 err = -EBADF;
0160 break;
0161 }
0162 if (copy_from_user(®s, uregs, sizeof(regs))) {
0163 err = -EFAULT;
0164 break;
0165 }
0166 err = rdmsr_safe_regs_on_cpu(cpu, regs);
0167 if (err)
0168 break;
0169 if (copy_to_user(uregs, ®s, sizeof(regs)))
0170 err = -EFAULT;
0171 break;
0172
0173 case X86_IOC_WRMSR_REGS:
0174 if (!(file->f_mode & FMODE_WRITE)) {
0175 err = -EBADF;
0176 break;
0177 }
0178 if (copy_from_user(®s, uregs, sizeof(regs))) {
0179 err = -EFAULT;
0180 break;
0181 }
0182 err = security_locked_down(LOCKDOWN_MSR);
0183 if (err)
0184 break;
0185
0186 err = filter_write(regs[1]);
0187 if (err)
0188 return err;
0189
0190 add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
0191
0192 err = wrmsr_safe_regs_on_cpu(cpu, regs);
0193 if (err)
0194 break;
0195 if (copy_to_user(uregs, ®s, sizeof(regs)))
0196 err = -EFAULT;
0197 break;
0198
0199 default:
0200 err = -ENOTTY;
0201 break;
0202 }
0203
0204 return err;
0205 }
0206
0207 static int msr_open(struct inode *inode, struct file *file)
0208 {
0209 unsigned int cpu = iminor(file_inode(file));
0210 struct cpuinfo_x86 *c;
0211
0212 if (!capable(CAP_SYS_RAWIO))
0213 return -EPERM;
0214
0215 if (cpu >= nr_cpu_ids || !cpu_online(cpu))
0216 return -ENXIO;
0217
0218 c = &cpu_data(cpu);
0219 if (!cpu_has(c, X86_FEATURE_MSR))
0220 return -EIO;
0221
0222 return 0;
0223 }
0224
0225
0226
0227
0228 static const struct file_operations msr_fops = {
0229 .owner = THIS_MODULE,
0230 .llseek = no_seek_end_llseek,
0231 .read = msr_read,
0232 .write = msr_write,
0233 .open = msr_open,
0234 .unlocked_ioctl = msr_ioctl,
0235 .compat_ioctl = msr_ioctl,
0236 };
0237
0238 static int msr_device_create(unsigned int cpu)
0239 {
0240 struct device *dev;
0241
0242 dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
0243 "msr%d", cpu);
0244 return PTR_ERR_OR_ZERO(dev);
0245 }
0246
0247 static int msr_device_destroy(unsigned int cpu)
0248 {
0249 device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
0250 return 0;
0251 }
0252
0253 static char *msr_devnode(struct device *dev, umode_t *mode)
0254 {
0255 return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
0256 }
0257
0258 static int __init msr_init(void)
0259 {
0260 int err;
0261
0262 if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
0263 pr_err("unable to get major %d for msr\n", MSR_MAJOR);
0264 return -EBUSY;
0265 }
0266 msr_class = class_create(THIS_MODULE, "msr");
0267 if (IS_ERR(msr_class)) {
0268 err = PTR_ERR(msr_class);
0269 goto out_chrdev;
0270 }
0271 msr_class->devnode = msr_devnode;
0272
0273 err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
0274 msr_device_create, msr_device_destroy);
0275 if (err < 0)
0276 goto out_class;
0277 cpuhp_msr_state = err;
0278 return 0;
0279
0280 out_class:
0281 class_destroy(msr_class);
0282 out_chrdev:
0283 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
0284 return err;
0285 }
0286 module_init(msr_init);
0287
0288 static void __exit msr_exit(void)
0289 {
0290 cpuhp_remove_state(cpuhp_msr_state);
0291 class_destroy(msr_class);
0292 __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
0293 }
0294 module_exit(msr_exit)
0295
0296 static int set_allow_writes(const char *val, const struct kernel_param *cp)
0297 {
0298
0299 char *s = strstrip((char *)val);
0300
0301 if (!strcmp(s, "on"))
0302 allow_writes = MSR_WRITES_ON;
0303 else if (!strcmp(s, "off"))
0304 allow_writes = MSR_WRITES_OFF;
0305 else
0306 allow_writes = MSR_WRITES_DEFAULT;
0307
0308 return 0;
0309 }
0310
0311 static int get_allow_writes(char *buf, const struct kernel_param *kp)
0312 {
0313 const char *res;
0314
0315 switch (allow_writes) {
0316 case MSR_WRITES_ON: res = "on"; break;
0317 case MSR_WRITES_OFF: res = "off"; break;
0318 default: res = "default"; break;
0319 }
0320
0321 return sprintf(buf, "%s\n", res);
0322 }
0323
0324 static const struct kernel_param_ops allow_writes_ops = {
0325 .set = set_allow_writes,
0326 .get = get_allow_writes
0327 };
0328
0329 module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600);
0330
0331 MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
0332 MODULE_DESCRIPTION("x86 generic MSR driver");
0333 MODULE_LICENSE("GPL");