1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * /dev/mcelog driver
  4 *
  5 * K8 parts Copyright 2002,2003 Andi Kleen, SuSE Labs.
  6 * Rest from unknown author(s).
  7 * 2004 Andi Kleen. Rewrote most of it.
  8 * Copyright 2008 Intel Corporation
  9 * Author: Andi Kleen
 10 */
 11
 12#include <linux/miscdevice.h>
 13#include <linux/slab.h>
 14#include <linux/kmod.h>
 15#include <linux/poll.h>
 16
 17#include "internal.h"
 18
 19static BLOCKING_NOTIFIER_HEAD(mce_injector_chain);
 20
 21static DEFINE_MUTEX(mce_chrdev_read_mutex);
 22
 23static char mce_helper[128];
 24static char *mce_helper_argv[2] = { mce_helper, NULL };
 25
 26/*
 27 * Lockless MCE logging infrastructure.
 28 * This avoids deadlocks on printk locks without having to break locks. Also
 29 * separate MCEs from kernel messages to avoid bogus bug reports.
 30 */
 31
 32static struct mce_log_buffer mcelog = {
 33	.signature	= MCE_LOG_SIGNATURE,
 34	.len		= MCE_LOG_LEN,
 35	.recordlen	= sizeof(struct mce),
 36};
 37
 38static DECLARE_WAIT_QUEUE_HEAD(mce_chrdev_wait);
 39
 40static int dev_mce_log(struct notifier_block *nb, unsigned long val,
 41				void *data)
 42{
 43	struct mce *mce = (struct mce *)data;
 44	unsigned int entry;
 45
 46	mutex_lock(&mce_chrdev_read_mutex);
 47
 48	entry = mcelog.next;
 49
 50	/*
 51	 * When the buffer fills up discard new entries. Assume that the
 52	 * earlier errors are the more interesting ones:
 53	 */
 54	if (entry >= MCE_LOG_LEN) {
 55		set_bit(MCE_OVERFLOW, (unsigned long *)&mcelog.flags);
 56		goto unlock;
 57	}
 58
 59	mcelog.next = entry + 1;
 60
 61	memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
 62	mcelog.entry[entry].finished = 1;
 63
 64	/* wake processes polling /dev/mcelog */
 65	wake_up_interruptible(&mce_chrdev_wait);
 66
 67unlock:
 68	mutex_unlock(&mce_chrdev_read_mutex);
 69
 70	return NOTIFY_OK;
 71}
 72
 73static struct notifier_block dev_mcelog_nb = {
 74	.notifier_call	= dev_mce_log,
 75	.priority	= MCE_PRIO_MCELOG,
 76};
 77
 78static void mce_do_trigger(struct work_struct *work)
 79{
 80	call_usermodehelper(mce_helper, mce_helper_argv, NULL, UMH_NO_WAIT);
 81}
 82
 83static DECLARE_WORK(mce_trigger_work, mce_do_trigger);
 84
 85
 86void mce_work_trigger(void)
 87{
 88	if (mce_helper[0])
 89		schedule_work(&mce_trigger_work);
 90}
 91
 92static ssize_t
 93show_trigger(struct device *s, struct device_attribute *attr, char *buf)
 94{
 95	strcpy(buf, mce_helper);
 96	strcat(buf, "\n");
 97	return strlen(mce_helper) + 1;
 98}
 99
100static ssize_t set_trigger(struct device *s, struct device_attribute *attr,
101				const char *buf, size_t siz)
102{
103	char *p;
104
105	strncpy(mce_helper, buf, sizeof(mce_helper));
106	mce_helper[sizeof(mce_helper)-1] = 0;
107	p = strchr(mce_helper, '\n');
108
109	if (p)
110		*p = 0;
111
112	return strlen(mce_helper) + !!p;
113}
114
115DEVICE_ATTR(trigger, 0644, show_trigger, set_trigger);
116
117/*
118 * mce_chrdev: Character device /dev/mcelog to read and clear the MCE log.
119 */
120
121static DEFINE_SPINLOCK(mce_chrdev_state_lock);
122static int mce_chrdev_open_count;	/* #times opened */
123static int mce_chrdev_open_exclu;	/* already open exclusive? */
124
125static int mce_chrdev_open(struct inode *inode, struct file *file)
126{
127	spin_lock(&mce_chrdev_state_lock);
128
129	if (mce_chrdev_open_exclu ||
130	    (mce_chrdev_open_count && (file->f_flags & O_EXCL))) {
131		spin_unlock(&mce_chrdev_state_lock);
132
133		return -EBUSY;
134	}
135
136	if (file->f_flags & O_EXCL)
137		mce_chrdev_open_exclu = 1;
138	mce_chrdev_open_count++;
139
140	spin_unlock(&mce_chrdev_state_lock);
141
142	return nonseekable_open(inode, file);
143}
144
145static int mce_chrdev_release(struct inode *inode, struct file *file)
146{
147	spin_lock(&mce_chrdev_state_lock);
148
149	mce_chrdev_open_count--;
150	mce_chrdev_open_exclu = 0;
151
152	spin_unlock(&mce_chrdev_state_lock);
153
154	return 0;
155}
156
157static int mce_apei_read_done;
158
159/* Collect MCE record of previous boot in persistent storage via APEI ERST. */
160static int __mce_read_apei(char __user **ubuf, size_t usize)
161{
162	int rc;
163	u64 record_id;
164	struct mce m;
165
166	if (usize < sizeof(struct mce))
167		return -EINVAL;
168
169	rc = apei_read_mce(&m, &record_id);
170	/* Error or no more MCE record */
171	if (rc <= 0) {
172		mce_apei_read_done = 1;
173		/*
174		 * When ERST is disabled, mce_chrdev_read() should return
175		 * "no record" instead of "no device."
176		 */
177		if (rc == -ENODEV)
178			return 0;
179		return rc;
180	}
181	rc = -EFAULT;
182	if (copy_to_user(*ubuf, &m, sizeof(struct mce)))
183		return rc;
184	/*
185	 * In fact, we should have cleared the record after that has
186	 * been flushed to the disk or sent to network in
187	 * /sbin/mcelog, but we have no interface to support that now,
188	 * so just clear it to avoid duplication.
189	 */
190	rc = apei_clear_mce(record_id);
191	if (rc) {
192		mce_apei_read_done = 1;
193		return rc;
194	}
195	*ubuf += sizeof(struct mce);
196
197	return 0;
198}
199
200static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
201				size_t usize, loff_t *off)
202{
203	char __user *buf = ubuf;
204	unsigned next;
205	int i, err;
206
207	mutex_lock(&mce_chrdev_read_mutex);
208
209	if (!mce_apei_read_done) {
210		err = __mce_read_apei(&buf, usize);
211		if (err || buf != ubuf)
212			goto out;
213	}
214
215	/* Only supports full reads right now */
216	err = -EINVAL;
217	if (*off != 0 || usize < MCE_LOG_LEN*sizeof(struct mce))
218		goto out;
219
220	next = mcelog.next;
221	err = 0;
222
223	for (i = 0; i < next; i++) {
224		struct mce *m = &mcelog.entry[i];
225
226		err |= copy_to_user(buf, m, sizeof(*m));
227		buf += sizeof(*m);
228	}
229
230	memset(mcelog.entry, 0, next * sizeof(struct mce));
231	mcelog.next = 0;
232
233	if (err)
234		err = -EFAULT;
235
236out:
237	mutex_unlock(&mce_chrdev_read_mutex);
238
239	return err ? err : buf - ubuf;
240}
241
242static __poll_t mce_chrdev_poll(struct file *file, poll_table *wait)
243{
244	poll_wait(file, &mce_chrdev_wait, wait);
245	if (READ_ONCE(mcelog.next))
246		return EPOLLIN | EPOLLRDNORM;
247	if (!mce_apei_read_done && apei_check_mce())
248		return EPOLLIN | EPOLLRDNORM;
249	return 0;
250}
251
252static long mce_chrdev_ioctl(struct file *f, unsigned int cmd,
253				unsigned long arg)
254{
255	int __user *p = (int __user *)arg;
256
257	if (!capable(CAP_SYS_ADMIN))
258		return -EPERM;
259
260	switch (cmd) {
261	case MCE_GET_RECORD_LEN:
262		return put_user(sizeof(struct mce), p);
263	case MCE_GET_LOG_LEN:
264		return put_user(MCE_LOG_LEN, p);
265	case MCE_GETCLEAR_FLAGS: {
266		unsigned flags;
267
268		do {
269			flags = mcelog.flags;
270		} while (cmpxchg(&mcelog.flags, flags, 0) != flags);
271
272		return put_user(flags, p);
273	}
274	default:
275		return -ENOTTY;
276	}
277}
278
279void mce_register_injector_chain(struct notifier_block *nb)
280{
281	blocking_notifier_chain_register(&mce_injector_chain, nb);
282}
283EXPORT_SYMBOL_GPL(mce_register_injector_chain);
284
285void mce_unregister_injector_chain(struct notifier_block *nb)
286{
287	blocking_notifier_chain_unregister(&mce_injector_chain, nb);
288}
289EXPORT_SYMBOL_GPL(mce_unregister_injector_chain);
290
291static ssize_t mce_chrdev_write(struct file *filp, const char __user *ubuf,
292				size_t usize, loff_t *off)
293{
294	struct mce m;
295
296	if (!capable(CAP_SYS_ADMIN))
297		return -EPERM;
298	/*
299	 * There are some cases where real MSR reads could slip
300	 * through.
301	 */
302	if (!boot_cpu_has(X86_FEATURE_MCE) || !boot_cpu_has(X86_FEATURE_MCA))
303		return -EIO;
304
305	if ((unsigned long)usize > sizeof(struct mce))
306		usize = sizeof(struct mce);
307	if (copy_from_user(&m, ubuf, usize))
308		return -EFAULT;
309
310	if (m.extcpu >= num_possible_cpus() || !cpu_online(m.extcpu))
311		return -EINVAL;
312
313	/*
314	 * Need to give user space some time to set everything up,
315	 * so do it a jiffie or two later everywhere.
316	 */
317	schedule_timeout(2);
318
319	blocking_notifier_call_chain(&mce_injector_chain, 0, &m);
320
321	return usize;
322}
323
324static const struct file_operations mce_chrdev_ops = {
325	.open			= mce_chrdev_open,
326	.release		= mce_chrdev_release,
327	.read			= mce_chrdev_read,
328	.write			= mce_chrdev_write,
329	.poll			= mce_chrdev_poll,
330	.unlocked_ioctl		= mce_chrdev_ioctl,
331	.llseek			= no_llseek,
332};
333
334static struct miscdevice mce_chrdev_device = {
335	MISC_MCELOG_MINOR,
336	"mcelog",
337	&mce_chrdev_ops,
338};
339
340static __init int dev_mcelog_init_device(void)
341{
342	int err;
343
344	/* register character device /dev/mcelog */
345	err = misc_register(&mce_chrdev_device);
346	if (err) {
347		if (err == -EBUSY)
348			/* Xen dom0 might have registered the device already. */
349			pr_info("Unable to init device /dev/mcelog, already registered");
350		else
351			pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);
352
353		return err;
354	}
355
356	mce_register_decode_chain(&dev_mcelog_nb);
357	return 0;
358}
359device_initcall_sync(dev_mcelog_init_device);