summaryrefslogtreecommitdiff
path: root/arch/x86/kernel/msr.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/kernel/msr.c')
-rw-r--r--arch/x86/kernel/msr.c233
1 files changed, 132 insertions, 101 deletions
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index ce130493b802..4469c784eaa0 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -1,14 +1,9 @@
+// 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
*
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
- * USA; either version 2 of the License, or (at your option) any later
- * version; incorporated herein by reference.
- *
* ----------------------------------------------------------------------- */
/*
@@ -22,6 +17,8 @@
* 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>
@@ -37,33 +34,20 @@
#include <linux/notifier.h>
#include <linux/uaccess.h>
#include <linux/gfp.h>
+#include <linux/security.h>
-#include <asm/processor.h>
+#include <asm/cpufeature.h>
#include <asm/msr.h>
-static struct class *msr_class;
+static enum cpuhp_state cpuhp_msr_state;
-static loff_t msr_seek(struct file *file, loff_t offset, int orig)
-{
- loff_t ret;
- struct inode *inode = file->f_mapping->host;
-
- mutex_lock(&inode->i_mutex);
- switch (orig) {
- case 0:
- file->f_pos = offset;
- ret = file->f_pos;
- break;
- case 1:
- file->f_pos += offset;
- ret = file->f_pos;
- break;
- default:
- ret = -EINVAL;
- }
- mutex_unlock(&inode->i_mutex);
- return ret;
-}
+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)
@@ -93,6 +77,34 @@ static ssize_t msr_read(struct file *file, char __user *buf,
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), tainting CPU_OUT_OF_SPEC.\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)
{
@@ -103,6 +115,14 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
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 */
@@ -111,9 +131,13 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
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;
}
@@ -134,14 +158,14 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
err = -EBADF;
break;
}
- if (copy_from_user(&regs, uregs, sizeof regs)) {
+ 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))
+ if (copy_to_user(uregs, &regs, sizeof(regs)))
err = -EFAULT;
break;
@@ -150,14 +174,24 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
err = -EBADF;
break;
}
- if (copy_from_user(&regs, uregs, sizeof regs)) {
+ 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))
+ if (copy_to_user(uregs, &regs, sizeof(regs)))
err = -EFAULT;
break;
@@ -192,7 +226,7 @@ static int msr_open(struct inode *inode, struct file *file)
*/
static const struct file_operations msr_fops = {
.owner = THIS_MODULE,
- .llseek = msr_seek,
+ .llseek = no_seek_end_llseek,
.read = msr_read,
.write = msr_write,
.open = msr_open,
@@ -200,104 +234,101 @@ static const struct file_operations msr_fops = {
.compat_ioctl = msr_ioctl,
};
-static int __cpuinit msr_device_create(int cpu)
+static char *msr_devnode(const struct device *dev, umode_t *mode)
{
- struct device *dev;
-
- dev = device_create(msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
- "msr%d", cpu);
- return IS_ERR(dev) ? PTR_ERR(dev) : 0;
+ return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
}
-static void msr_device_destroy(int cpu)
-{
- device_destroy(msr_class, MKDEV(MSR_MAJOR, cpu));
-}
+static const struct class msr_class = {
+ .name = "msr",
+ .devnode = msr_devnode,
+};
-static int __cpuinit msr_class_cpu_callback(struct notifier_block *nfb,
- unsigned long action, void *hcpu)
+static int msr_device_create(unsigned int cpu)
{
- unsigned int cpu = (unsigned long)hcpu;
- int err = 0;
+ struct device *dev;
- switch (action) {
- case CPU_UP_PREPARE:
- err = msr_device_create(cpu);
- break;
- case CPU_UP_CANCELED:
- case CPU_UP_CANCELED_FROZEN:
- case CPU_DEAD:
- msr_device_destroy(cpu);
- break;
- }
- return notifier_from_errno(err);
+ dev = device_create(&msr_class, NULL, MKDEV(MSR_MAJOR, cpu), NULL,
+ "msr%d", cpu);
+ return PTR_ERR_OR_ZERO(dev);
}
-static struct notifier_block __refdata msr_class_cpu_notifier = {
- .notifier_call = msr_class_cpu_callback,
-};
-
-static char *msr_devnode(struct device *dev, umode_t *mode)
+static int msr_device_destroy(unsigned int cpu)
{
- return kasprintf(GFP_KERNEL, "cpu/%u/msr", MINOR(dev->devt));
+ device_destroy(&msr_class, MKDEV(MSR_MAJOR, cpu));
+ return 0;
}
static int __init msr_init(void)
{
- int i, err = 0;
- i = 0;
+ int err;
if (__register_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr", &msr_fops)) {
- printk(KERN_ERR "msr: unable to get major %d for msr\n",
- MSR_MAJOR);
- err = -EBUSY;
- goto out;
+ 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);
+ err = class_register(&msr_class);
+ if (err)
goto out_chrdev;
- }
- msr_class->devnode = msr_devnode;
- get_online_cpus();
- for_each_online_cpu(i) {
- err = msr_device_create(i);
- if (err != 0)
- goto out_class;
- }
- register_hotcpu_notifier(&msr_class_cpu_notifier);
- put_online_cpus();
- err = 0;
- goto out;
+ 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:
- i = 0;
- for_each_online_cpu(i)
- msr_device_destroy(i);
- put_online_cpus();
- class_destroy(msr_class);
+ class_unregister(&msr_class);
out_chrdev:
__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
-out:
return err;
}
+module_init(msr_init);
static void __exit msr_exit(void)
{
- int cpu = 0;
- get_online_cpus();
- for_each_online_cpu(cpu)
- msr_device_destroy(cpu);
- class_destroy(msr_class);
+ cpuhp_remove_state(cpuhp_msr_state);
+ class_unregister(&msr_class);
__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
- unregister_hotcpu_notifier(&msr_class_cpu_notifier);
- put_online_cpus();
}
-
-module_init(msr_init);
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");
generated by cgit (git 2.34.1) at 2025-12-25 06:17:43 +0000