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, 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                 GFP_ATOMIC);
 179         bpf_task_storage_unlock();
 180
 181         err = PTR_ERR_OR_ZERO(sdata);
 182 out:
 183         put_pid(pid);
 184         return err;
 185 }
 186
 187 static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
 188 {
 189         struct bpf_local_storage_data *sdata;
 190
 191         sdata = task_storage_lookup(task, map, false);
 192         if (!sdata)
 193                 return -ENOENT;
 194
 195         bpf_selem_unlink(SELEM(sdata), true);
 196
 197         return 0;
 198 }
 199
 200 static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
 201 {
 202         struct task_struct *task;
 203         unsigned int f_flags;
 204         struct pid *pid;
 205         int fd, err;
 206
 207         fd = *(int *)key;
 208         pid = pidfd_get_pid(fd, &f_flags);
 209         if (IS_ERR(pid))
 210                 return PTR_ERR(pid);
 211
 212         /* We should be in an RCU read side critical section, it should be safe
 213          * to call pid_task.
 214          */
 215         WARN_ON_ONCE(!rcu_read_lock_held());
 216         task = pid_task(pid, PIDTYPE_PID);
 217         if (!task) {
 218                 err = -ENOENT;
 219                 goto out;
 220         }
 221
 222         bpf_task_storage_lock();
 223         err = task_storage_delete(task, map);
 224         bpf_task_storage_unlock();
 225 out:
 226         put_pid(pid);
 227         return err;
 228 }
 229
 230 /* *gfp_flags* is a hidden argument provided by the verifier */
 231 BPF_CALL_5(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
 232            task, void *, value, u64, flags, gfp_t, gfp_flags)
 233 {
 234         struct bpf_local_storage_data *sdata;
 235
 236         WARN_ON_ONCE(!bpf_rcu_lock_held());
 237         if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
 238                 return (unsigned long)NULL;
 239
 240         if (!task)
 241                 return (unsigned long)NULL;
 242
 243         if (!bpf_task_storage_trylock())
 244                 return (unsigned long)NULL;
 245
 246         sdata = task_storage_lookup(task, map, true);
 247         if (sdata)
 248                 goto unlock;
 249
 250         /* only allocate new storage, when the task is refcounted */
 251         if (refcount_read(&task->usage) &&
 252             (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
 253                 sdata = bpf_local_storage_update(
 254                         task, (struct bpf_local_storage_map *)map, value,
 255                         BPF_NOEXIST, gfp_flags);
 256
 257 unlock:
 258         bpf_task_storage_unlock();
 259         return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL :
 260                 (unsigned long)sdata->data;
 261 }
 262
 263 BPF_CALL_2(bpf_task_storage_delete, struct bpf_map *, map, struct task_struct *,
 264            task)
 265 {
 266         int ret;
 267
 268         WARN_ON_ONCE(!bpf_rcu_lock_held());
 269         if (!task)
 270                 return -EINVAL;
 271
 272         if (!bpf_task_storage_trylock())
 273                 return -EBUSY;
 274
 275         /* This helper must only be called from places where the lifetime of the task
 276          * is guaranteed. Either by being refcounted or by being protected
 277          * by an RCU read-side critical section.
 278          */
 279         ret = task_storage_delete(task, map);
 280         bpf_task_storage_unlock();
 281         return ret;
 282 }
 283
 284 static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
 285 {
 286         return -ENOTSUPP;
 287 }
 288
 289 static struct bpf_map *task_storage_map_alloc(union bpf_attr *attr)
 290 {
 291         struct bpf_local_storage_map *smap;
 292
 293         smap = bpf_local_storage_map_alloc(attr);
 294         if (IS_ERR(smap))
 295                 return ERR_CAST(smap);
 296
 297         smap->cache_idx = bpf_local_storage_cache_idx_get(&task_cache);
 298         return &smap->map;
 299 }
 300
 301 static void task_storage_map_free(struct bpf_map *map)
 302 {
 303         struct bpf_local_storage_map *smap;
 304
 305         smap = (struct bpf_local_storage_map *)map;
 306         bpf_local_storage_cache_idx_free(&task_cache, smap->cache_idx);
 307         bpf_local_storage_map_free(smap, &bpf_task_storage_busy);
 308 }
 309
 310 BTF_ID_LIST_SINGLE(task_storage_map_btf_ids, struct, bpf_local_storage_map)
 311 const struct bpf_map_ops task_storage_map_ops = {
 312         .map_meta_equal = bpf_map_meta_equal,
 313         .map_alloc_check = bpf_local_storage_map_alloc_check,
 314         .map_alloc = task_storage_map_alloc,
 315         .map_free = task_storage_map_free,
 316         .map_get_next_key = notsupp_get_next_key,
 317         .map_lookup_elem = bpf_pid_task_storage_lookup_elem,
 318         .map_update_elem = bpf_pid_task_storage_update_elem,
 319         .map_delete_elem = bpf_pid_task_storage_delete_elem,
 320         .map_check_btf = bpf_local_storage_map_check_btf,
 321         .map_btf_id = &task_storage_map_btf_ids[0],
 322         .map_owner_storage_ptr = task_storage_ptr,
 323 };
 324
 325 const struct bpf_func_proto bpf_task_storage_get_proto = {
 326         .func = bpf_task_storage_get,
 327         .gpl_only = false,
 328         .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
 329         .arg1_type = ARG_CONST_MAP_PTR,
 330         .arg2_type = ARG_PTR_TO_BTF_ID,
 331         .arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
 332         .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
 333         .arg4_type = ARG_ANYTHING,
 334 };
 335
 336 const struct bpf_func_proto bpf_task_storage_delete_proto = {
 337         .func = bpf_task_storage_delete,
 338         .gpl_only = false,
 339         .ret_type = RET_INTEGER,
 340         .arg1_type = ARG_CONST_MAP_PTR,
 341         .arg2_type = ARG_PTR_TO_BTF_ID,
 342         .arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
 343 };