// SPDX-License-Identifier: GPL-2.0-only
/*
 * /dev/mcelog driver
 *
 * K8 parts Copyright 2002,2003 Andi Kleen, SuSE Labs.
 * Rest from unknown author(s).
 * 2004 Andi Kleen. Rewrote most of it.
 * Copyright 2008 Intel Corporation
 * Author: Andi Kleen
 */

#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/poll.h>

#include "internal.h"

static BLOCKING_NOTIFIER_HEAD(mce_injector_chain);

static DEFINE_MUTEX(mce_chrdev_read_mutex);

static char mce_helper[128];
static char *mce_helper_argv[2] = { mce_helper, NULL };

/*
 * Lockless MCE logging infrastructure.
 * This avoids deadlocks on printk locks without having to break locks. Also
 * separate MCEs from kernel messages to avoid bogus bug reports.
 */

static struct mce_log_buffer *mcelog;

static DECLARE_WAIT_QUEUE_HEAD(mce_chrdev_wait);

static int dev_mce_log(struct notifier_block *nb, unsigned long val,
                                void *data)
{
        struct mce *mce = (struct mce *)data;
        unsigned int entry;

        if (mce->kflags & MCE_HANDLED_CEC)
                return NOTIFY_DONE;

        mutex_lock(&mce_chrdev_read_mutex);

        entry = mcelog->next;

        /*
         * When the buffer fills up discard new entries. Assume that the
         * earlier errors are the more interesting ones:
         */
        if (entry >= mcelog->len) {
                set_bit(MCE_OVERFLOW, (unsigned long *)&mcelog->flags);
                goto unlock;
        }

        mcelog->next = entry + 1;

        memcpy(mcelog->entry + entry, mce, sizeof(struct mce));
        mcelog->entry[entry].finished = 1;
        mcelog->entry[entry].kflags = 0;

        /* wake processes polling /dev/mcelog */
        wake_up_interruptible(&mce_chrdev_wait);

unlock:
        mutex_unlock(&mce_chrdev_read_mutex);

        if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
                mce->kflags |= MCE_HANDLED_MCELOG;

        return NOTIFY_OK;
}

static struct notifier_block dev_mcelog_nb = {
        .notifier_call  = dev_mce_log,
        .priority       = MCE_PRIO_MCELOG,
};

static void mce_do_trigger(struct work_struct *work)
{
        call_usermodehelper(mce_helper, mce_helper_argv, NULL, UMH_NO_WAIT);
}

static DECLARE_WORK(mce_trigger_work, mce_do_trigger);


void mce_work_trigger(void)
{
        if (mce_helper[0])
                schedule_work(&mce_trigger_work);
}

static ssize_t
show_trigger(struct device *s, struct device_attribute *attr, char *buf)
{
        strcpy(buf, mce_helper);
        strcat(buf, "\n");
        return strlen(mce_helper) + 1;
}

static ssize_t set_trigger(struct device *s, struct device_attribute *attr,
                                const char *buf, size_t siz)
{
        char *p;

        strscpy(mce_helper, buf, sizeof(mce_helper));
        p = strchr(mce_helper, '\n');

        if (p)
                *p = 0;

        return strlen(mce_helper) + !!p;
}

DEVICE_ATTR(trigger, 0644, show_trigger, set_trigger);

/*
 * mce_chrdev: Character device /dev/mcelog to read and clear the MCE log.
 */

static DEFINE_SPINLOCK(mce_chrdev_state_lock);
static int mce_chrdev_open_count;       /* #times opened */
static int mce_chrdev_open_exclu;       /* already open exclusive? */

static int mce_chrdev_open(struct inode *inode, struct file *file)
{
        spin_lock(&mce_chrdev_state_lock);

        if (mce_chrdev_open_exclu ||
            (mce_chrdev_open_count && (file->f_flags & O_EXCL))) {
                spin_unlock(&mce_chrdev_state_lock);

                return -EBUSY;
        }

        if (file->f_flags & O_EXCL)
                mce_chrdev_open_exclu = 1;
        mce_chrdev_open_count++;

        spin_unlock(&mce_chrdev_state_lock);

        return nonseekable_open(inode, file);
}

static int mce_chrdev_release(struct inode *inode, struct file *file)
{
        spin_lock(&mce_chrdev_state_lock);

        mce_chrdev_open_count--;
        mce_chrdev_open_exclu = 0;

        spin_unlock(&mce_chrdev_state_lock);

        return 0;
}

static int mce_apei_read_done;

/* Collect MCE record of previous boot in persistent storage via APEI ERST. */
static int __mce_read_apei(char __user **ubuf, size_t usize)
{
        int rc;
        u64 record_id;
        struct mce m;

        if (usize < sizeof(struct mce))
                return -EINVAL;

        rc = apei_read_mce(&m, &record_id);
        /* Error or no more MCE record */
        if (rc <= 0) {
                mce_apei_read_done = 1;
                /*
                 * When ERST is disabled, mce_chrdev_read() should return
                 * "no record" instead of "no device."
                 */
                if (rc == -ENODEV)
                        return 0;
                return rc;
        }
        rc = -EFAULT;
        if (copy_to_user(*ubuf, &m, sizeof(struct mce)))
                return rc;
        /*
         * In fact, we should have cleared the record after that has
         * been flushed to the disk or sent to network in
         * /sbin/mcelog, but we have no interface to support that now,
         * so just clear it to avoid duplication.
         */
        rc = apei_clear_mce(record_id);
        if (rc) {
                mce_apei_read_done = 1;
                return rc;
        }
        *ubuf += sizeof(struct mce);

        return 0;
}

static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
                                size_t usize, loff_t *off)
{
        char __user *buf = ubuf;
        unsigned next;
        int i, err;

        mutex_lock(&mce_chrdev_read_mutex);

        if (!mce_apei_read_done) {
                err = __mce_read_apei(&buf, usize);
                if (err || buf != ubuf)
                        goto out;
        }

        /* Only supports full reads right now */
        err = -EINVAL;
        if (*off != 0 || usize < mcelog->len * sizeof(struct mce))
                goto out;

        next = mcelog->next;
        err = 0;

        for (i = 0; i < next; i++) {
                struct mce *m = &mcelog->entry[i];

                err |= copy_to_user(buf, m, sizeof(*m));
                buf += sizeof(*m);
        }

        memset(mcelog->entry, 0, next * sizeof(struct mce));
        mcelog->next = 0;

        if (err)
                err = -EFAULT;

out:
        mutex_unlock(&mce_chrdev_read_mutex);

        return err ? err : buf - ubuf;
}

static __poll_t mce_chrdev_poll(struct file *file, poll_table *wait)
{
        poll_wait(file, &mce_chrdev_wait, wait);
        if (READ_ONCE(mcelog->next))
                return EPOLLIN | EPOLLRDNORM;
        if (!mce_apei_read_done && apei_check_mce())
                return EPOLLIN | EPOLLRDNORM;
        return 0;
}

static long mce_chrdev_ioctl(struct file *f, unsigned int cmd,
                                unsigned long arg)
{
        int __user *p = (int __user *)arg;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        switch (cmd) {
        case MCE_GET_RECORD_LEN:
                return put_user(sizeof(struct mce), p);
        case MCE_GET_LOG_LEN:
                return put_user(mcelog->len, p);
        case MCE_GETCLEAR_FLAGS:
                return put_user(xchg(&mcelog->flags, 0), p);
        default:
                return -ENOTTY;
        }
}

void mce_register_injector_chain(struct notifier_block *nb)
{
        blocking_notifier_chain_register(&mce_injector_chain, nb);
}
EXPORT_SYMBOL_GPL(mce_register_injector_chain);

void mce_unregister_injector_chain(struct notifier_block *nb)
{
        blocking_notifier_chain_unregister(&mce_injector_chain, nb);
}
EXPORT_SYMBOL_GPL(mce_unregister_injector_chain);

static ssize_t mce_chrdev_write(struct file *filp, const char __user *ubuf,
                                size_t usize, loff_t *off)
{
        struct mce m;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
        /*
         * There are some cases where real MSR reads could slip
         * through.
         */
        if (!boot_cpu_has(X86_FEATURE_MCE) || !boot_cpu_has(X86_FEATURE_MCA))
                return -EIO;

        if ((unsigned long)usize > sizeof(struct mce))
                usize = sizeof(struct mce);
        if (copy_from_user(&m, ubuf, usize))
                return -EFAULT;

        if (m.extcpu >= num_possible_cpus() || !cpu_online(m.extcpu))
                return -EINVAL;

        /*
         * Need to give user space some time to set everything up,
         * so do it a jiffy or two later everywhere.
         */
        schedule_timeout(2);

        blocking_notifier_call_chain(&mce_injector_chain, 0, &m);

        return usize;
}

static const struct file_operations mce_chrdev_ops = {
        .open                   = mce_chrdev_open,
        .release                = mce_chrdev_release,
        .read                   = mce_chrdev_read,
        .write                  = mce_chrdev_write,
        .poll                   = mce_chrdev_poll,
        .unlocked_ioctl         = mce_chrdev_ioctl,
        .compat_ioctl           = compat_ptr_ioctl,
};

static struct miscdevice mce_chrdev_device = {
        MISC_MCELOG_MINOR,
        "mcelog",
        &mce_chrdev_ops,
};

static __init int dev_mcelog_init_device(void)
{
        int mce_log_len;
        int err;

        mce_log_len = max(MCE_LOG_MIN_LEN, num_online_cpus());
        mcelog = kzalloc_flex(*mcelog, entry, mce_log_len);
        if (!mcelog)
                return -ENOMEM;

        memcpy(mcelog->signature, MCE_LOG_SIGNATURE, sizeof(mcelog->signature));
        mcelog->len = mce_log_len;
        mcelog->recordlen = sizeof(struct mce);

        /* register character device /dev/mcelog */
        err = misc_register(&mce_chrdev_device);
        if (err) {
                if (err == -EBUSY)
                        /* Xen dom0 might have registered the device already. */
                        pr_info("Unable to init device /dev/mcelog, already registered");
                else
                        pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);

                kfree(mcelog);
                return err;
        }

        mce_register_decode_chain(&dev_mcelog_nb);
        return 0;
}
device_initcall_sync(dev_mcelog_init_device);