kernel/bpf/bpf_task_storage.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (c) 2020 Facebook
   4  * Copyright 2020 Google LLC.
   5  */
   6
   7 #include <linux/pid.h>
   8 #include <linux/sched.h>
   9 #include <linux/rculist.h>
  10 #include <linux/list.h>
  11 #include <linux/hash.h>
  12 #include <linux/types.h>
  13 #include <linux/spinlock.h>
  14 #include <linux/bpf.h>
  15 #include <linux/bpf_local_storage.h>
  16 #include <linux/filter.h>
  17 #include <uapi/linux/btf.h>
  18 #include <linux/btf_ids.h>
  19 #include <linux/fdtable.h>
  20
  21 DEFINE_BPF_STORAGE_CACHE(task_cache);
  22
  23 static DEFINE_PER_CPU(int, bpf_task_storage_busy);
  24
  25 static void bpf_task_storage_lock(void)
  26 {
  27         migrate_disable();
  28         __this_cpu_inc(bpf_task_storage_busy);
  29 }
  30
  31 static void bpf_task_storage_unlock(void)
  32 {
  33         __this_cpu_dec(bpf_task_storage_busy);
  34         migrate_enable();
  35 }
  36
  37 static bool bpf_task_storage_trylock(void)
  38 {
  39         migrate_disable();
  40         if (unlikely(__this_cpu_inc_return(bpf_task_storage_busy) != 1)) {
  41                 __this_cpu_dec(bpf_task_storage_busy);
  42                 migrate_enable();
  43                 return false;
  44         }
  45         return true;
  46 }
  47
  48 static struct bpf_local_storage __rcu **task_storage_ptr(void *owner)
  49 {
  50         struct task_struct *task = owner;
  51
  52         return &task->bpf_storage;
  53 }
  54
  55 static struct bpf_local_storage_data *
  56 task_storage_lookup(struct task_struct *task, struct bpf_map *map,
  57                     bool cacheit_lockit)
  58 {
  59         struct bpf_local_storage *task_storage;
  60         struct bpf_local_storage_map *smap;
  61
  62         task_storage = rcu_dereference(task->bpf_storage);
  63         if (!task_storage)
  64                 return NULL;
  65
  66         smap = (struct bpf_local_storage_map *)map;
  67         return bpf_local_storage_lookup(task_storage, smap, cacheit_lockit);
  68 }
  69
  70 void bpf_task_storage_free(struct task_struct *task)
  71 {
  72         struct bpf_local_storage_elem *selem;
  73         struct bpf_local_storage *local_storage;
  74         bool free_task_storage = false;
  75         struct hlist_node *n;
  76         unsigned long flags;
  77
  78         rcu_read_lock();
  79
  80         local_storage = rcu_dereference(task->bpf_storage);
  81         if (!local_storage) {
  82                 rcu_read_unlock();
  83                 return;
  84         }
  85
  86         /* Neither the bpf_prog nor the bpf-map's syscall
  87          * could be modifying the local_storage->list now.
  88          * Thus, no elem can be added-to or deleted-from the
  89          * local_storage->list by the bpf_prog or by the bpf-map's syscall.
  90          *
  91          * It is racing with bpf_local_storage_map_free() alone
  92          * when unlinking elem from the local_storage->list and
  93          * the map's bucket->list.
  94          */
  95         bpf_task_storage_lock();
  96         raw_spin_lock_irqsave(&local_storage->lock, flags);
  97         hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
  98                 /* Always unlink from map before unlinking from
  99                  * local_storage.
 100                  */
 101                 bpf_selem_unlink_map(selem);
 102                 free_task_storage = bpf_selem_unlink_storage_nolock(
 103                         local_storage, selem, false);
 104         }
 105         raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 106         bpf_task_storage_unlock();
 107         rcu_read_unlock();
 108
 109         /* free_task_storage should always be true as long as
 110          * local_storage->list was non-empty.
 111          */
 112         if (free_task_storage)
 113                 kfree_rcu(local_storage, rcu);
 114 }
 115
 116 static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key)
 117 {
 118         struct bpf_local_storage_data *sdata;
 119         struct task_struct *task;
 120         unsigned int f_flags;
 121         struct pid *pid;
 122         int fd, err;
 123
 124         fd = *(int *)key;
 125         pid = pidfd_get_pid(fd, &f_flags);
 126         if (IS_ERR(pid))
 127                 return ERR_CAST(pid);
 128
 129         /* We should be in an RCU read side critical section, it should be safe
 130          * to call pid_task.
 131          */
 132         WARN_ON_ONCE(!rcu_read_lock_held());
 133         task = pid_task(pid, PIDTYPE_PID);
 134         if (!task) {
 135                 err = -ENOENT;
 136                 goto out;
 137         }
 138
 139         bpf_task_storage_lock();
 140         sdata = task_storage_lookup(task, map, true);
 141         bpf_task_storage_unlock();
 142         put_pid(pid);
 143         return sdata ? sdata->data : NULL;
 144 out:
 145         put_pid(pid);
 146         return ERR_PTR(err);
 147 }
 148
 149 static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
 150                                             void *value, u64 map_flags)
 151 {
 152         struct bpf_local_storage_data *sdata;
 153         struct task_struct *task;
 154         unsigned int f_flags;
 155         struct pid *pid;
 156         int fd, err;
 157
 158         fd = *(int *)key;
 159         pid = pidfd_get_pid(fd, &f_flags);
 160         if (IS_ERR(pid))
 161                 return PTR_ERR(pid);
 162
 163         /* We should be in an RCU read side critical section, it should be safe
 164          * to call pid_task.
 165          */
 166         WARN_ON_ONCE(!rcu_read_lock_held());
 167         task = pid_task(pid, PIDTYPE_PID);
 168         if (!task) {
 169                 err = -ENOENT;
 170                 goto out;
 171         }
 172
 173         bpf_task_storage_lock();
 174         sdata = bpf_local_storage_update(
 175                 task, (struct bpf_local_storage_map *)map, value, map_flags);
 176         bpf_task_storage_unlock();
 177
 178         err = PTR_ERR_OR_ZERO(sdata);
 179 out:
 180         put_pid(pid);
 181         return err;
 182 }
 183
 184 static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
 185 {
 186         struct bpf_local_storage_data *sdata;
 187
 188         sdata = task_storage_lookup(task, map, false);
 189         if (!sdata)
 190                 return -ENOENT;
 191
 192         bpf_selem_unlink(SELEM(sdata));
 193
 194         return 0;
 195 }
 196
 197 static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
 198 {
 199         struct task_struct *task;
 200         unsigned int f_flags;
 201         struct pid *pid;
 202         int fd, err;
 203
 204         fd = *(int *)key;
 205         pid = pidfd_get_pid(fd, &f_flags);
 206         if (IS_ERR(pid))
 207                 return PTR_ERR(pid);
 208
 209         /* We should be in an RCU read side critical section, it should be safe
 210          * to call pid_task.
 211          */
 212         WARN_ON_ONCE(!rcu_read_lock_held());
 213         task = pid_task(pid, PIDTYPE_PID);
 214         if (!task) {
 215                 err = -ENOENT;
 216                 goto out;
 217         }
 218
 219         bpf_task_storage_lock();
 220         err = task_storage_delete(task, map);
 221         bpf_task_storage_unlock();
 222 out:
 223         put_pid(pid);
 224         return err;
 225 }
 226
 227 BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
 228            task, void *, value, u64, flags)
 229 {
 230         struct bpf_local_storage_data *sdata;
 231
 232         if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
 233                 return (unsigned long)NULL;
 234
 235         if (!task)
 236                 return (unsigned long)NULL;
 237
 238         if (!bpf_task_storage_trylock())
 239                 return (unsigned long)NULL;
 240
 241         sdata = task_storage_lookup(task, map, true);
 242         if (sdata)
 243                 goto unlock;
 244
 245         /* only allocate new storage, when the task is refcounted */
 246         if (refcount_read(&task->usage) &&
 247             (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
 248                 sdata = bpf_local_storage_update(
 249                         task, (struct bpf_local_storage_map *)map, value,
 250                         BPF_NOEXIST);
 251
 252 unlock:
 253         bpf_task_storage_unlock();
 254         return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL :
 255                 (unsigned long)sdata->data;
 256 }
 257
 258 BPF_CALL_2(bpf_task_storage_delete, struct bpf_map *, map, struct task_struct *,
 259            task)
 260 {
 261         int ret;
 262
 263         if (!task)
 264                 return -EINVAL;
 265
 266         if (!bpf_task_storage_trylock())
 267                 return -EBUSY;
 268
 269         /* This helper must only be called from places where the lifetime of the task
 270          * is guaranteed. Either by being refcounted or by being protected
 271          * by an RCU read-side critical section.
 272          */
 273         ret = task_storage_delete(task, map);
 274         bpf_task_storage_unlock();
 275         return ret;
 276 }
 277
 278 static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
 279 {
 280         return -ENOTSUPP;
 281 }
 282
 283 static struct bpf_map *task_storage_map_alloc(union bpf_attr *attr)
 284 {
 285         struct bpf_local_storage_map *smap;
 286
 287         smap = bpf_local_storage_map_alloc(attr);
 288         if (IS_ERR(smap))
 289                 return ERR_CAST(smap);
 290
 291         smap->cache_idx = bpf_local_storage_cache_idx_get(&task_cache);
 292         return &smap->map;
 293 }
 294
 295 static void task_storage_map_free(struct bpf_map *map)
 296 {
 297         struct bpf_local_storage_map *smap;
 298
 299         smap = (struct bpf_local_storage_map *)map;
 300         bpf_local_storage_cache_idx_free(&task_cache, smap->cache_idx);
 301         bpf_local_storage_map_free(smap, &bpf_task_storage_busy);
 302 }
 303
 304 static int task_storage_map_btf_id;
 305 const struct bpf_map_ops task_storage_map_ops = {
 306         .map_meta_equal = bpf_map_meta_equal,
 307         .map_alloc_check = bpf_local_storage_map_alloc_check,
 308         .map_alloc = task_storage_map_alloc,
 309         .map_free = task_storage_map_free,
 310         .map_get_next_key = notsupp_get_next_key,
 311         .map_lookup_elem = bpf_pid_task_storage_lookup_elem,
 312         .map_update_elem = bpf_pid_task_storage_update_elem,
 313         .map_delete_elem = bpf_pid_task_storage_delete_elem,
 314         .map_check_btf = bpf_local_storage_map_check_btf,
 315         .map_btf_name = "bpf_local_storage_map",
 316         .map_btf_id = &task_storage_map_btf_id,
 317         .map_owner_storage_ptr = task_storage_ptr,
 318 };
 319
 320 BTF_ID_LIST_SINGLE(bpf_task_storage_btf_ids, struct, task_struct)
 321
 322 const struct bpf_func_proto bpf_task_storage_get_proto = {
 323         .func = bpf_task_storage_get,
 324         .gpl_only = false,
 325         .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
 326         .arg1_type = ARG_CONST_MAP_PTR,
 327         .arg2_type = ARG_PTR_TO_BTF_ID,
 328         .arg2_btf_id = &bpf_task_storage_btf_ids[0],
 329         .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
 330         .arg4_type = ARG_ANYTHING,
 331 };
 332
 333 const struct bpf_func_proto bpf_task_storage_delete_proto = {
 334         .func = bpf_task_storage_delete,
 335         .gpl_only = false,
 336         .ret_type = RET_INTEGER,
 337         .arg1_type = ARG_CONST_MAP_PTR,
 338         .arg2_type = ARG_PTR_TO_BTF_ID,
 339         .arg2_btf_id = &bpf_task_storage_btf_ids[0],
 340 };