diff options
Diffstat (limited to '')
| -rw-r--r-- | arch/x86/kernel/msr.c | 333 |
1 files changed, 333 insertions, 0 deletions
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c new file mode 100644 index 000000000..ed8ac6bcb --- /dev/null +++ b/arch/x86/kernel/msr.c @@ -0,0 +1,333 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* ----------------------------------------------------------------------- * + * + * Copyright 2000-2008 H. Peter Anvin - All Rights Reserved + * Copyright 2009 Intel Corporation; author: H. Peter Anvin + * + * ----------------------------------------------------------------------- */ + +/* + * x86 MSR access device + * + * This device is accessed by lseek() to the appropriate register number + * and then read/write in chunks of 8 bytes. A larger size means multiple + * reads or writes of the same register. + * + * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on + * an SMP box will direct the access to CPU %d. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/module.h> + +#include <linux/types.h> +#include <linux/errno.h> +#include <linux/fcntl.h> +#include <linux/init.h> +#include <linux/poll.h> +#include <linux/smp.h> +#include <linux/major.h> +#include <linux/fs.h> +#include <linux/device.h> +#include <linux/cpu.h> +#include <linux/notifier.h> +#include <linux/uaccess.h> +#include <linux/gfp.h> +#include <linux/security.h> + +#include <asm/cpufeature.h> +#include <asm/msr.h> + +static struct class *msr_class; +static enum cpuhp_state cpuhp_msr_state; + +enum allow_write_msrs { + MSR_WRITES_ON, + MSR_WRITES_OFF, + MSR_WRITES_DEFAULT, +}; + +static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT; + +static ssize_t msr_read(struct file *file, char __user *buf, + size_t count, loff_t *ppos) +{ + u32 __user *tmp = (u32 __user *) buf; + u32 data[2]; + u32 reg = *ppos; + int cpu = iminor(file_inode(file)); + int err = 0; + ssize_t bytes = 0; + + if (count % 8) + return -EINVAL; /* Invalid chunk size */ + + for (; count; count -= 8) { + err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]); + if (err) + break; + if (copy_to_user(tmp, &data, 8)) { + err = -EFAULT; + break; + } + tmp += 2; + bytes += 8; + } + + return bytes ? bytes : err; +} + +static int filter_write(u32 reg) +{ + /* + * MSRs writes usually happen all at once, and can easily saturate kmsg. + * Only allow one message every 30 seconds. + * + * It's possible to be smarter here and do it (for example) per-MSR, but + * it would certainly be more complex, and this is enough at least to + * avoid saturating the ring buffer. + */ + static DEFINE_RATELIMIT_STATE(fw_rs, 30 * HZ, 1); + + switch (allow_writes) { + case MSR_WRITES_ON: return 0; + case MSR_WRITES_OFF: return -EPERM; + default: break; + } + + if (!__ratelimit(&fw_rs)) + return 0; + + pr_warn("Write to unrecognized MSR 0x%x by %s (pid: %d).\n", + reg, current->comm, current->pid); + pr_warn("See https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/about for details.\n"); + + return 0; +} + +static ssize_t msr_write(struct file *file, const char __user *buf, + size_t count, loff_t *ppos) +{ + const u32 __user *tmp = (const u32 __user *)buf; + u32 data[2]; + u32 reg = *ppos; + int cpu = iminor(file_inode(file)); + int err = 0; + ssize_t bytes = 0; + + err = security_locked_down(LOCKDOWN_MSR); + if (err) + return err; + + err = filter_write(reg); + if (err) + return err; + + if (count % 8) + return -EINVAL; /* Invalid chunk size */ + + for (; count; count -= 8) { + if (copy_from_user(&data, tmp, 8)) { + err = -EFAULT; + break; + } + + add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK); + + err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]); + if (err) + break; + + tmp += 2; + bytes += 8; + } + + return bytes ? bytes : err; +} + +static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) +{ + u32 __user *uregs = (u32 __user *)arg; + u32 regs[8]; + int cpu = iminor(file_inode(file)); + int err; + + switch (ioc) { + case X86_IOC_RDMSR_REGS: + if (!(file->f_mode & FMODE_READ)) { + err = -EBADF; + break; + } + if (copy_from_user(®s, uregs, sizeof(regs))) { + err = -EFAULT; + break; + } + err = rdmsr_safe_regs_on_cpu(cpu, regs); + if (err) + break; + if (copy_to_user(uregs, ®s, sizeof(regs))) + err = -EFAULT; + break; + + case X86_IOC_WRMSR_REGS: + if (!(file->f_mode & FMODE_WRITE)) { + err = -EBADF; + break; + } + if (copy_from_user(®s, uregs, sizeof(regs))) { + err = -EFAULT; + break; + } + err = security_locked_down(LOCKDOWN_MSR); + if (err) + break; + + err = filter_write(regs[1]); + if (err) + return err; + + add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK); + + err = wrmsr_safe_regs_on_cpu(cpu, regs); + if (err) + break; + if (copy_to_user(uregs, ®s, sizeof(regs))) + err = -EFAULT; + break; + + default: + err = -ENOTTY; + break; + } + + return err; +} + +static int msr_open(struct inode *inode, struct file *file) +{ + unsigned int cpu = iminor(file_inode(file)); + struct cpuinfo_x86 *c; + + if (!capable(CAP_SYS_RAWIO)) + return -EPERM; + + if (cpu >= nr_cpu_ids || !cpu_online(cpu)) + return -ENXIO; /* No such CPU */ + + c = &cpu_data(cpu); + if (!cpu_has(c, X86_FEATURE_MSR)) + return -EIO; /* MSR not supported */ + + return 0; +} + +/* + * File operations we support + */ +static const struct file_operations msr_fops = { + .owner = THIS_MODULE, + .llseek = no_seek_end_llseek, + .read = msr_read, + .write = msr_write, + .open = msr_open, + .unlocked_ioctl = msr_ioctl, + .compat_ioctl = msr_ioctl, +}; + +static int msr_device_create(unsigned int cpu) +{ + struct device *dev; + + dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL, + "msr%d", cpu); + return PTR_ERR_OR_ZERO(dev); +} + +static int msr_device_destroy(unsigned int cpu) +{ + device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu)); + return 0; +} + +static char *msr_devnode(struct device *dev, umode_t *mode) +{ + return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt)); +} + +static int __init msr_init(void) +{ + int err; + + if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) { + pr_err("unable to get major %d for msr\n", MSR_MAJOR); + return -EBUSY; + } + msr_class = class_create(THIS_MODULE, "msr"); + if (IS_ERR(msr_class)) { + err = PTR_ERR(msr_class); + goto out_chrdev; + } + msr_class->devnode = msr_devnode; + + err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online", + msr_device_create, msr_device_destroy); + if (err < 0) + goto out_class; + cpuhp_msr_state = err; + return 0; + +out_class: + class_destroy(msr_class); +out_chrdev: + __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); + return err; +} +module_init(msr_init); + +static void __exit msr_exit(void) +{ + cpuhp_remove_state(cpuhp_msr_state); + class_destroy(msr_class); + __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); +} +module_exit(msr_exit) + +static int set_allow_writes(const char *val, const struct kernel_param *cp) +{ + /* val is NUL-terminated, see kernfs_fop_write() */ + char *s = strstrip((char *)val); + + if (!strcmp(s, "on")) + allow_writes = MSR_WRITES_ON; + else if (!strcmp(s, "off")) + allow_writes = MSR_WRITES_OFF; + else + allow_writes = MSR_WRITES_DEFAULT; + + return 0; +} + +static int get_allow_writes(char *buf, const struct kernel_param *kp) +{ + const char *res; + + switch (allow_writes) { + case MSR_WRITES_ON: res = "on"; break; + case MSR_WRITES_OFF: res = "off"; break; + default: res = "default"; break; + } + + return sprintf(buf, "%s\n", res); +} + +static const struct kernel_param_ops allow_writes_ops = { + .set = set_allow_writes, + .get = get_allow_writes +}; + +module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600); + +MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>"); +MODULE_DESCRIPTION("x86 generic MSR driver"); +MODULE_LICENSE("GPL"); |