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 #include <linux/rcupdate_trace.h>
  21
  22 DEFINE_BPF_STORAGE_CACHE(task_cache);
  23
  24 static DEFINE_PER_CPU(int, bpf_task_storage_busy);
  25
  26 static void bpf_task_storage_lock(void)
  27 {
  28         migrate_disable();
  29         __this_cpu_inc(bpf_task_storage_busy);
  30 }
  31
  32 static void bpf_task_storage_unlock(void)
  33 {
  34         __this_cpu_dec(bpf_task_storage_busy);
  35         migrate_enable();
  36 }
  37
  38 static bool bpf_task_storage_trylock(void)
  39 {
  40         migrate_disable();
  41         if (unlikely(__this_cpu_inc_return(bpf_task_storage_busy) != 1)) {
  42                 __this_cpu_dec(bpf_task_storage_busy);
  43                 migrate_enable();
  44                 return false;
  45         }
  46         return true;
  47 }
  48
  49 static struct bpf_local_storage __rcu **task_storage_ptr(void *owner)
  50 {
  51         struct task_struct *task = owner;
  52
  53         return &task->bpf_storage;
  54 }
  55
  56 static struct bpf_local_storage_data *
  57 task_storage_lookup(struct task_struct *task, struct bpf_map *map,
  58                     bool cacheit_lockit)
  59 {
  60         struct bpf_local_storage *task_storage;
  61         struct bpf_local_storage_map *smap;
  62
  63         task_storage =
  64                 rcu_dereference_check(task->bpf_storage, bpf_rcu_lock_held());
  65         if (!task_storage)
  66                 return NULL;
  67
  68         smap = (struct bpf_local_storage_map *)map;
  69         return bpf_local_storage_lookup(task_storage, smap, cacheit_lockit);
  70 }
  71
  72 void bpf_task_storage_free(struct task_struct *task)
  73 {
  74         struct bpf_local_storage_elem *selem;
  75         struct bpf_local_storage *local_storage;
  76         bool free_task_storage = false;
  77         struct hlist_node *n;
  78         unsigned long flags;
  79
  80         rcu_read_lock();
  81
  82         local_storage = rcu_dereference(task->bpf_storage);
  83         if (!local_storage) {
  84                 rcu_read_unlock();
  85                 return;
  86         }
  87
  88         /* Neither the bpf_prog nor the bpf-map's syscall
  89          * could be modifying the local_storage->list now.
  90          * Thus, no elem can be added-to or deleted-from the
  91          * local_storage->list by the bpf_prog or by the bpf-map's syscall.
  92          *
  93          * It is racing with bpf_local_storage_map_free() alone
  94          * when unlinking elem from the local_storage->list and
  95          * the map's bucket->list.
  96          */
  97         bpf_task_storage_lock();
  98         raw_spin_lock_irqsave(&local_storage->lock, flags);
  99         hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
 100                 /* Always unlink from map before unlinking from
 101                  * local_storage.
 102                  */
 103                 bpf_selem_unlink_map(selem);
 104                 free_task_storage = bpf_selem_unlink_storage_nolock(
 105                         local_storage, selem, false);
 106         }
 107         raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 108         bpf_task_storage_unlock();
 109         rcu_read_unlock();
 110
 111         /* free_task_storage should always be true as long as
 112          * local_storage->list was non-empty.
 113          */
 114         if (free_task_storage)
 115                 kfree_rcu(local_storage, rcu);
 116 }
 117
 118 static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key)
 119 {
 120         struct bpf_local_storage_data *sdata;
 121         struct task_struct *task;
 122         unsigned int f_flags;
 123         struct pid *pid;
 124         int fd, err;
 125
 126         fd = *(int *)key;
 127         pid = pidfd_get_pid(fd, &f_flags);
 128         if (IS_ERR(pid))
 129                 return ERR_CAST(pid);
 130
 131         /* We should be in an RCU read side critical section, it should be safe
 132          * to call pid_task.
 133          */
 134         WARN_ON_ONCE(!rcu_read_lock_held());
 135         task = pid_task(pid, PIDTYPE_PID);
 136         if (!task) {
 137                 err = -ENOENT;
 138                 goto out;
 139         }
 140
 141         bpf_task_storage_lock();
 142         sdata = task_storage_lookup(task, map, true);
 143         bpf_task_storage_unlock();
 144         put_pid(pid);
 145         return sdata ? sdata->data : NULL;
 146 out:
 147         put_pid(pid);
 148         return ERR_PTR(err);
 149 }
 150
 151 static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
 152                                             void *value, u64 map_flags)
 153 {
 154         struct bpf_local_storage_data *sdata;
 155         struct task_struct *task;
 156         unsigned int f_flags;
 157         struct pid *pid;
 158         int fd, err;
 159
 160         fd = *(int *)key;
 161         pid = pidfd_get_pid(fd, &f_flags);
 162         if (IS_ERR(pid))
 163                 return PTR_ERR(pid);
 164
 165         /* We should be in an RCU read side critical section, it should be safe
 166          * to call pid_task.
 167          */
 168         WARN_ON_ONCE(!rcu_read_lock_held());
 169         task = pid_task(pid, PIDTYPE_PID);
 170         if (!task) {
 171                 err = -ENOENT;
 172                 goto out;
 173         }
 174
 175         bpf_task_storage_lock();
 176         sdata = bpf_local_storage_update(
 177                 task, (struct bpf_local_storage_map *)map, value, map_flags);
 178         bpf_task_storage_unlock();
 179
 180         err = PTR_ERR_OR_ZERO(sdata);
 181 out:
 182         put_pid(pid);
 183         return err;
 184 }
 185
 186 static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
 187 {
 188         struct bpf_local_storage_data *sdata;
 189
 190         sdata = task_storage_lookup(task, map, false);
 191         if (!sdata)
 192                 return -ENOENT;
 193
 194         bpf_selem_unlink(SELEM(sdata));
 195
 196         return 0;
 197 }
 198
 199 static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
 200 {
 201         struct task_struct *task;
 202         unsigned int f_flags;
 203         struct pid *pid;
 204         int fd, err;
 205
 206         fd = *(int *)key;
 207         pid = pidfd_get_pid(fd, &f_flags);
 208         if (IS_ERR(pid))
 209                 return PTR_ERR(pid);
 210
 211         /* We should be in an RCU read side critical section, it should be safe
 212          * to call pid_task.
 213          */
 214         WARN_ON_ONCE(!rcu_read_lock_held());
 215         task = pid_task(pid, PIDTYPE_PID);
 216         if (!task) {
 217                 err = -ENOENT;
 218                 goto out;
 219         }
 220
 221         bpf_task_storage_lock();
 222         err = task_storage_delete(task, map);
 223         bpf_task_storage_unlock();
 224 out:
 225         put_pid(pid);
 226         return err;
 227 }
 228
 229 BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
 230            task, void *, value, u64, flags)
 231 {
 232         struct bpf_local_storage_data *sdata;
 233
 234         WARN_ON_ONCE(!bpf_rcu_lock_held());
 235         if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
 236                 return (unsigned long)NULL;
 237
 238         if (!task)
 239                 return (unsigned long)NULL;
 240
 241         if (!bpf_task_storage_trylock())
 242                 return (unsigned long)NULL;
 243
 244         sdata = task_storage_lookup(task, map, true);
 245         if (sdata)
 246                 goto unlock;
 247
 248         /* only allocate new storage, when the task is refcounted */
 249         if (refcount_read(&task->usage) &&
 250             (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
 251                 sdata = bpf_local_storage_update(
 252                         task, (struct bpf_local_storage_map *)map, value,
 253                         BPF_NOEXIST);
 254
 255 unlock:
 256         bpf_task_storage_unlock();
 257         return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL :
 258                 (unsigned long)sdata->data;
 259 }
 260
 261 BPF_CALL_2(bpf_task_storage_delete, struct bpf_map *, map, struct task_struct *,
 262            task)
 263 {
 264         int ret;
 265
 266         WARN_ON_ONCE(!bpf_rcu_lock_held());
 267         if (!task)
 268                 return -EINVAL;
 269
 270         if (!bpf_task_storage_trylock())
 271                 return -EBUSY;
 272
 273         /* This helper must only be called from places where the lifetime of the task
 274          * is guaranteed. Either by being refcounted or by being protected
 275          * by an RCU read-side critical section.
 276          */
 277         ret = task_storage_delete(task, map);
 278         bpf_task_storage_unlock();
 279         return ret;
 280 }
 281
 282 static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
 283 {
 284         return -ENOTSUPP;
 285 }
 286
 287 static struct bpf_map *task_storage_map_alloc(union bpf_attr *attr)
 288 {
 289         struct bpf_local_storage_map *smap;
 290
 291         smap = bpf_local_storage_map_alloc(attr);
 292         if (IS_ERR(smap))
 293                 return ERR_CAST(smap);
 294
 295         smap->cache_idx = bpf_local_storage_cache_idx_get(&task_cache);
 296         return &smap->map;
 297 }
 298
 299 static void task_storage_map_free(struct bpf_map *map)
 300 {
 301         struct bpf_local_storage_map *smap;
 302
 303         smap = (struct bpf_local_storage_map *)map;
 304         bpf_local_storage_cache_idx_free(&task_cache, smap->cache_idx);
 305         bpf_local_storage_map_free(smap, &bpf_task_storage_busy);
 306 }
 307
 308 static int task_storage_map_btf_id;
 309 const struct bpf_map_ops task_storage_map_ops = {
 310         .map_meta_equal = bpf_map_meta_equal,
 311         .map_alloc_check = bpf_local_storage_map_alloc_check,
 312         .map_alloc = task_storage_map_alloc,
 313         .map_free = task_storage_map_free,
 314         .map_get_next_key = notsupp_get_next_key,
 315         .map_lookup_elem = bpf_pid_task_storage_lookup_elem,
 316         .map_update_elem = bpf_pid_task_storage_update_elem,
 317         .map_delete_elem = bpf_pid_task_storage_delete_elem,
 318         .map_check_btf = bpf_local_storage_map_check_btf,
 319         .map_btf_name = "bpf_local_storage_map",
 320         .map_btf_id = &task_storage_map_btf_id,
 321         .map_owner_storage_ptr = task_storage_ptr,
 322 };
 323
 324 const struct bpf_func_proto bpf_task_storage_get_proto = {
 325         .func = bpf_task_storage_get,
 326         .gpl_only = false,
 327         .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
 328         .arg1_type = ARG_CONST_MAP_PTR,
 329         .arg2_type = ARG_PTR_TO_BTF_ID,
 330         .arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
 331         .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
 332         .arg4_type = ARG_ANYTHING,
 333 };
 334
 335 const struct bpf_func_proto bpf_task_storage_delete_proto = {
 336         .func = bpf_task_storage_delete,
 337         .gpl_only = false,
 338         .ret_type = RET_INTEGER,
 339         .arg1_type = ARG_CONST_MAP_PTR,
 340         .arg2_type = ARG_PTR_TO_BTF_ID,
 341         .arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
 342 };