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