1 files changed, 334 insertions, 0 deletions
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
new file mode 100644
index 000000000..e17c16c54
--- /dev/null
+++ b/arch/x86/kernel/msr.c
@@ -0,0 +1,334 @@
+// 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 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(&regs, uregs, sizeof(regs))) {
+			err = -EFAULT;
+			break;
+		}
+		err = rdmsr_safe_regs_on_cpu(cpu, regs);
+		if (err)
+			break;
+		if (copy_to_user(uregs, &regs, sizeof(regs)))
+			err = -EFAULT;
+		break;
+
+	case X86_IOC_WRMSR_REGS:
+		if (!(file->f_mode & FMODE_WRITE)) {
+			err = -EBADF;
+			break;
+		}
+		if (copy_from_user(&regs, 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, &regs, 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 char *msr_devnode(const struct device *dev, umode_t *mode)
+{
+	return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
+}
+
+static const struct class msr_class = {
+	.name		= "msr",
+	.devnode	= msr_devnode,
+};
+
+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 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;
+	}
+	err = class_register(&msr_class);
+	if (err)
+		goto out_chrdev;
+
+	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_unregister(&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_unregister(&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");