kernel/fail_function.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fail_function.c: Function-based error injection
   4  */
   5 #include <linux/error-injection.h>
   6 #include <linux/debugfs.h>
   7 #include <linux/fault-inject.h>
   8 #include <linux/kallsyms.h>
   9 #include <linux/kprobes.h>
  10 #include <linux/module.h>
  11 #include <linux/mutex.h>
  12 #include <linux/slab.h>
  13 #include <linux/uaccess.h>
  14
  15 static int fei_kprobe_handler(struct kprobe *kp, struct pt_regs *regs);
  16
  17 static void fei_post_handler(struct kprobe *kp, struct pt_regs *regs,
  18                              unsigned long flags)
  19 {
  20         /*
  21          * A dummy post handler is required to prohibit optimizing, because
  22          * jump optimization does not support execution path overriding.
  23          */
  24 }
  25
  26 struct fei_attr {
  27         struct list_head list;
  28         struct kprobe kp;
  29         unsigned long retval;
  30 };
  31 static DEFINE_MUTEX(fei_lock);
  32 static LIST_HEAD(fei_attr_list);
  33 static DECLARE_FAULT_ATTR(fei_fault_attr);
  34 static struct dentry *fei_debugfs_dir;
  35
  36 static unsigned long adjust_error_retval(unsigned long addr, unsigned long retv)
  37 {
  38         switch (get_injectable_error_type(addr)) {
  39         case EI_ETYPE_NULL:
  40                 if (retv != 0)
  41                         return 0;
  42                 break;
  43         case EI_ETYPE_ERRNO:
  44                 if (retv < (unsigned long)-MAX_ERRNO)
  45                         return (unsigned long)-EINVAL;
  46                 break;
  47         case EI_ETYPE_ERRNO_NULL:
  48                 if (retv != 0 && retv < (unsigned long)-MAX_ERRNO)
  49                         return (unsigned long)-EINVAL;
  50                 break;
  51         }
  52
  53         return retv;
  54 }
  55
  56 static struct fei_attr *fei_attr_new(const char *sym, unsigned long addr)
  57 {
  58         struct fei_attr *attr;
  59
  60         attr = kzalloc(sizeof(*attr), GFP_KERNEL);
  61         if (attr) {
  62                 attr->kp.symbol_name = kstrdup(sym, GFP_KERNEL);
  63                 if (!attr->kp.symbol_name) {
  64                         kfree(attr);
  65                         return NULL;
  66                 }
  67                 attr->kp.pre_handler = fei_kprobe_handler;
  68                 attr->kp.post_handler = fei_post_handler;
  69                 attr->retval = adjust_error_retval(addr, 0);
  70                 INIT_LIST_HEAD(&attr->list);
  71         }
  72         return attr;
  73 }
  74
  75 static void fei_attr_free(struct fei_attr *attr)
  76 {
  77         if (attr) {
  78                 kfree(attr->kp.symbol_name);
  79                 kfree(attr);
  80         }
  81 }
  82
  83 static struct fei_attr *fei_attr_lookup(const char *sym)
  84 {
  85         struct fei_attr *attr;
  86
  87         list_for_each_entry(attr, &fei_attr_list, list) {
  88                 if (!strcmp(attr->kp.symbol_name, sym))
  89                         return attr;
  90         }
  91
  92         return NULL;
  93 }
  94
  95 static bool fei_attr_is_valid(struct fei_attr *_attr)
  96 {
  97         struct fei_attr *attr;
  98
  99         list_for_each_entry(attr, &fei_attr_list, list) {
 100                 if (attr == _attr)
 101                         return true;
 102         }
 103
 104         return false;
 105 }
 106
 107 static int fei_retval_set(void *data, u64 val)
 108 {
 109         struct fei_attr *attr = data;
 110         unsigned long retv = (unsigned long)val;
 111         int err = 0;
 112
 113         mutex_lock(&fei_lock);
 114         /*
 115          * Since this operation can be done after retval file is removed,
 116          * It is safer to check the attr is still valid before accessing
 117          * its member.
 118          */
 119         if (!fei_attr_is_valid(attr)) {
 120                 err = -ENOENT;
 121                 goto out;
 122         }
 123
 124         if (attr->kp.addr) {
 125                 if (adjust_error_retval((unsigned long)attr->kp.addr,
 126                                         val) != retv)
 127                         err = -EINVAL;
 128         }
 129         if (!err)
 130                 attr->retval = val;
 131 out:
 132         mutex_unlock(&fei_lock);
 133
 134         return err;
 135 }
 136
 137 static int fei_retval_get(void *data, u64 *val)
 138 {
 139         struct fei_attr *attr = data;
 140         int err = 0;
 141
 142         mutex_lock(&fei_lock);
 143         /* Here we also validate @attr to ensure it still exists. */
 144         if (!fei_attr_is_valid(attr))
 145                 err = -ENOENT;
 146         else
 147                 *val = attr->retval;
 148         mutex_unlock(&fei_lock);
 149
 150         return err;
 151 }
 152 DEFINE_DEBUGFS_ATTRIBUTE(fei_retval_ops, fei_retval_get, fei_retval_set,
 153                          "%llx\n");
 154
 155 static int fei_debugfs_add_attr(struct fei_attr *attr)
 156 {
 157         struct dentry *dir;
 158
 159         dir = debugfs_create_dir(attr->kp.symbol_name, fei_debugfs_dir);
 160         if (!dir)
 161                 return -ENOMEM;
 162
 163         if (!debugfs_create_file("retval", 0600, dir, attr, &fei_retval_ops)) {
 164                 debugfs_remove_recursive(dir);
 165                 return -ENOMEM;
 166         }
 167
 168         return 0;
 169 }
 170
 171 static void fei_debugfs_remove_attr(struct fei_attr *attr)
 172 {
 173         struct dentry *dir;
 174
 175         dir = debugfs_lookup(attr->kp.symbol_name, fei_debugfs_dir);
 176         if (dir)
 177                 debugfs_remove_recursive(dir);
 178 }
 179
 180 static int fei_kprobe_handler(struct kprobe *kp, struct pt_regs *regs)
 181 {
 182         struct fei_attr *attr = container_of(kp, struct fei_attr, kp);
 183
 184         if (should_fail(&fei_fault_attr, 1)) {
 185                 regs_set_return_value(regs, attr->retval);
 186                 override_function_with_return(regs);
 187                 /* Kprobe specific fixup */
 188                 reset_current_kprobe();
 189                 preempt_enable_no_resched();
 190                 return 1;
 191         }
 192
 193         return 0;
 194 }
 195 NOKPROBE_SYMBOL(fei_kprobe_handler)
 196
 197 static void *fei_seq_start(struct seq_file *m, loff_t *pos)
 198 {
 199         mutex_lock(&fei_lock);
 200         return seq_list_start(&fei_attr_list, *pos);
 201 }
 202
 203 static void fei_seq_stop(struct seq_file *m, void *v)
 204 {
 205         mutex_unlock(&fei_lock);
 206 }
 207
 208 static void *fei_seq_next(struct seq_file *m, void *v, loff_t *pos)
 209 {
 210         return seq_list_next(v, &fei_attr_list, pos);
 211 }
 212
 213 static int fei_seq_show(struct seq_file *m, void *v)
 214 {
 215         struct fei_attr *attr = list_entry(v, struct fei_attr, list);
 216
 217         seq_printf(m, "%pf\n", attr->kp.addr);
 218         return 0;
 219 }
 220
 221 static const struct seq_operations fei_seq_ops = {
 222         .start  = fei_seq_start,
 223         .next   = fei_seq_next,
 224         .stop   = fei_seq_stop,
 225         .show   = fei_seq_show,
 226 };
 227
 228 static int fei_open(struct inode *inode, struct file *file)
 229 {
 230         return seq_open(file, &fei_seq_ops);
 231 }
 232
 233 static void fei_attr_remove(struct fei_attr *attr)
 234 {
 235         fei_debugfs_remove_attr(attr);
 236         unregister_kprobe(&attr->kp);
 237         list_del(&attr->list);
 238         fei_attr_free(attr);
 239 }
 240
 241 static void fei_attr_remove_all(void)
 242 {
 243         struct fei_attr *attr, *n;
 244
 245         list_for_each_entry_safe(attr, n, &fei_attr_list, list) {
 246                 fei_attr_remove(attr);
 247         }
 248 }
 249
 250 static ssize_t fei_write(struct file *file, const char __user *buffer,
 251                          size_t count, loff_t *ppos)
 252 {
 253         struct fei_attr *attr;
 254         unsigned long addr;
 255         char *buf, *sym;
 256         int ret;
 257
 258         /* cut off if it is too long */
 259         if (count > KSYM_NAME_LEN)
 260                 count = KSYM_NAME_LEN;
 261         buf = kmalloc(sizeof(char) * (count + 1), GFP_KERNEL);
 262         if (!buf)
 263                 return -ENOMEM;
 264
 265         if (copy_from_user(buf, buffer, count)) {
 266                 ret = -EFAULT;
 267                 goto out;
 268         }
 269         buf[count] = '\0';
 270         sym = strstrip(buf);
 271
 272         mutex_lock(&fei_lock);
 273
 274         /* Writing just spaces will remove all injection points */
 275         if (sym[0] == '\0') {
 276                 fei_attr_remove_all();
 277                 ret = count;
 278                 goto out;
 279         }
 280         /* Writing !function will remove one injection point */
 281         if (sym[0] == '!') {
 282                 attr = fei_attr_lookup(sym + 1);
 283                 if (!attr) {
 284                         ret = -ENOENT;
 285                         goto out;
 286                 }
 287                 fei_attr_remove(attr);
 288                 ret = count;
 289                 goto out;
 290         }
 291
 292         addr = kallsyms_lookup_name(sym);
 293         if (!addr) {
 294                 ret = -EINVAL;
 295                 goto out;
 296         }
 297         if (!within_error_injection_list(addr)) {
 298                 ret = -ERANGE;
 299                 goto out;
 300         }
 301         if (fei_attr_lookup(sym)) {
 302                 ret = -EBUSY;
 303                 goto out;
 304         }
 305         attr = fei_attr_new(sym, addr);
 306         if (!attr) {
 307                 ret = -ENOMEM;
 308                 goto out;
 309         }
 310
 311         ret = register_kprobe(&attr->kp);
 312         if (!ret)
 313                 ret = fei_debugfs_add_attr(attr);
 314         if (ret < 0)
 315                 fei_attr_remove(attr);
 316         else {
 317                 list_add_tail(&attr->list, &fei_attr_list);
 318                 ret = count;
 319         }
 320 out:
 321         kfree(buf);
 322         mutex_unlock(&fei_lock);
 323         return ret;
 324 }
 325
 326 static const struct file_operations fei_ops = {
 327         .open =         fei_open,
 328         .read =         seq_read,
 329         .write =        fei_write,
 330         .llseek =       seq_lseek,
 331         .release =      seq_release,
 332 };
 333
 334 static int __init fei_debugfs_init(void)
 335 {
 336         struct dentry *dir;
 337
 338         dir = fault_create_debugfs_attr("fail_function", NULL,
 339                                         &fei_fault_attr);
 340         if (IS_ERR(dir))
 341                 return PTR_ERR(dir);
 342
 343         /* injectable attribute is just a symlink of error_inject/list */
 344         if (!debugfs_create_symlink("injectable", dir,
 345                                     "../error_injection/list"))
 346                 goto error;
 347
 348         if (!debugfs_create_file("inject", 0600, dir, NULL, &fei_ops))
 349                 goto error;
 350
 351         fei_debugfs_dir = dir;
 352
 353         return 0;
 354 error:
 355         debugfs_remove_recursive(dir);
 356         return -ENOMEM;
 357 }
 358
 359 late_initcall(fei_debugfs_init);