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Diffstat (limited to 'arch/x86/kernel/msr.c')
-rw-r--r--arch/x86/kernel/msr.c140
1 files changed, 115 insertions, 25 deletions
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index ef688804f80d..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.
- *
* ----------------------------------------------------------------------- */
/*
@@ -39,13 +34,21 @@
#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)
{
@@ -74,6 +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)
{
@@ -84,6 +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 */
@@ -92,9 +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;
}
@@ -115,14 +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;
@@ -131,14 +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;
@@ -181,26 +234,31 @@ static const struct file_operations msr_fops = {
.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,
+ 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));
+ 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;
@@ -209,12 +267,9 @@ static int __init msr_init(void)
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;
err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/msr:online",
msr_device_create, msr_device_destroy);
@@ -224,7 +279,7 @@ static int __init msr_init(void)
return 0;
out_class:
- class_destroy(msr_class);
+ class_unregister(&msr_class);
out_chrdev:
__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
return err;
@@ -234,11 +289,46 @@ module_init(msr_init);
static void __exit msr_exit(void)
{
cpuhp_remove_state(cpuhp_msr_state);
- class_destroy(msr_class);
+ 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");
generated by cgit (git 2.34.1) at 2025-12-25 08:06:00 +0000