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// 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;
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 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;
if (count % 8)
return -EINVAL; /* Invalid chunk size */
for (; count; count -= 8) {
if (copy_from_user(&data, tmp, 8)) {
err = -EFAULT;
break;
}
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 = 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)
MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
MODULE_DESCRIPTION("x86 generic MSR driver");
MODULE_LICENSE("GPL");
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