// SPDX-License-Identifier: GPL-2.0
// error-inject.c: Function-level error injection table
#include <linux/error-injection.h>
#include <linux/debugfs.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <asm/sections.h>

/* Whitelist of symbols that can be overridden for error injection. */
static LIST_HEAD(error_injection_list);
static DEFINE_MUTEX(ei_mutex);
struct ei_entry {
        struct list_head list;
        unsigned long start_addr;
        unsigned long end_addr;
        int etype;
        void *priv;
};

bool within_error_injection_list(unsigned long addr)
{
        struct ei_entry *ent;
        bool ret = false;

        mutex_lock(&ei_mutex);
        list_for_each_entry(ent, &error_injection_list, list) {
                if (addr >= ent->start_addr && addr < ent->end_addr) {
                        ret = true;
                        break;
                }
        }
        mutex_unlock(&ei_mutex);
        return ret;
}

int get_injectable_error_type(unsigned long addr)
{
        struct ei_entry *ent;
        int ei_type = -EINVAL;

        mutex_lock(&ei_mutex);
        list_for_each_entry(ent, &error_injection_list, list) {
                if (addr >= ent->start_addr && addr < ent->end_addr) {
                        ei_type = ent->etype;
                        break;
                }
        }
        mutex_unlock(&ei_mutex);

        return ei_type;
}

/*
 * Lookup and populate the error_injection_list.
 *
 * For safety reasons we only allow certain functions to be overridden with
 * bpf_error_injection, so we need to populate the list of the symbols that have
 * been marked as safe for overriding.
 */
static void populate_error_injection_list(struct error_injection_entry *start,
                                          struct error_injection_entry *end,
                                          void *priv)
{
        struct error_injection_entry *iter;
        struct ei_entry *ent;
        unsigned long entry, offset = 0, size = 0;

        mutex_lock(&ei_mutex);
        for (iter = start; iter < end; iter++) {
                entry = (unsigned long)dereference_symbol_descriptor((void *)iter->addr);

                if (!kernel_text_address(entry) ||
                    !kallsyms_lookup_size_offset(entry, &size, &offset)) {
                        pr_err("Failed to find error inject entry at %p\n",
                                (void *)entry);
                        continue;
                }

                ent = kmalloc_obj(*ent);
                if (!ent)
                        break;
                ent->start_addr = entry;
                ent->end_addr = entry + size;
                ent->etype = iter->etype;
                ent->priv = priv;
                INIT_LIST_HEAD(&ent->list);
                list_add_tail(&ent->list, &error_injection_list);
        }
        mutex_unlock(&ei_mutex);
}

/* Markers of the _error_inject_whitelist section */
extern struct error_injection_entry __start_error_injection_whitelist[];
extern struct error_injection_entry __stop_error_injection_whitelist[];

static void __init populate_kernel_ei_list(void)
{
        populate_error_injection_list(__start_error_injection_whitelist,
                                      __stop_error_injection_whitelist,
                                      NULL);
}

#ifdef CONFIG_MODULES
static void module_load_ei_list(struct module *mod)
{
        if (!mod->num_ei_funcs)
                return;

        populate_error_injection_list(mod->ei_funcs,
                                      mod->ei_funcs + mod->num_ei_funcs, mod);
}

static void module_unload_ei_list(struct module *mod)
{
        struct ei_entry *ent, *n;

        if (!mod->num_ei_funcs)
                return;

        mutex_lock(&ei_mutex);
        list_for_each_entry_safe(ent, n, &error_injection_list, list) {
                if (ent->priv == mod) {
                        list_del_init(&ent->list);
                        kfree(ent);
                }
        }
        mutex_unlock(&ei_mutex);
}

/* Module notifier call back, checking error injection table on the module */
static int ei_module_callback(struct notifier_block *nb,
                              unsigned long val, void *data)
{
        struct module *mod = data;

        if (val == MODULE_STATE_COMING)
                module_load_ei_list(mod);
        else if (val == MODULE_STATE_GOING)
                module_unload_ei_list(mod);

        return NOTIFY_DONE;
}

static struct notifier_block ei_module_nb = {
        .notifier_call = ei_module_callback,
        .priority = 0
};

static __init int module_ei_init(void)
{
        return register_module_notifier(&ei_module_nb);
}
#else /* !CONFIG_MODULES */
#define module_ei_init()        (0)
#endif

/*
 * error_injection/whitelist -- shows which functions can be overridden for
 * error injection.
 */
static void *ei_seq_start(struct seq_file *m, loff_t *pos)
{
        mutex_lock(&ei_mutex);
        return seq_list_start(&error_injection_list, *pos);
}

static void ei_seq_stop(struct seq_file *m, void *v)
{
        mutex_unlock(&ei_mutex);
}

static void *ei_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
        return seq_list_next(v, &error_injection_list, pos);
}

static const char *error_type_string(int etype)
{
        switch (etype) {
        case EI_ETYPE_NULL:
                return "NULL";
        case EI_ETYPE_ERRNO:
                return "ERRNO";
        case EI_ETYPE_ERRNO_NULL:
                return "ERRNO_NULL";
        case EI_ETYPE_TRUE:
                return "TRUE";
        default:
                return "(unknown)";
        }
}

static int ei_seq_show(struct seq_file *m, void *v)
{
        struct ei_entry *ent = list_entry(v, struct ei_entry, list);

        seq_printf(m, "%ps\t%s\n", (void *)ent->start_addr,
                   error_type_string(ent->etype));
        return 0;
}

static const struct seq_operations ei_sops = {
        .start = ei_seq_start,
        .next  = ei_seq_next,
        .stop  = ei_seq_stop,
        .show  = ei_seq_show,
};

DEFINE_SEQ_ATTRIBUTE(ei);

static int __init ei_debugfs_init(void)
{
        struct dentry *dir, *file;

        dir = debugfs_create_dir("error_injection", NULL);

        file = debugfs_create_file("list", 0444, dir, NULL, &ei_fops);
        if (!file) {
                debugfs_remove(dir);
                return -ENOMEM;
        }

        return 0;
}

static int __init init_error_injection(void)
{
        populate_kernel_ei_list();

        if (!module_ei_init())
                ei_debugfs_init();

        return 0;
}
late_initcall(init_error_injection);