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
bpf_task_storage_lock(void)25 static void bpf_task_storage_lock(void)
26 {
27 migrate_disable();
28 __this_cpu_inc(bpf_task_storage_busy);
29 }
30
bpf_task_storage_unlock(void)31 static void bpf_task_storage_unlock(void)
32 {
33 __this_cpu_dec(bpf_task_storage_busy);
34 migrate_enable();
35 }
36
bpf_task_storage_trylock(void)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
task_storage_ptr(void * owner)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 *
task_storage_lookup(struct task_struct * task,struct bpf_map * map,bool cacheit_lockit)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
bpf_task_storage_free(struct task_struct * task)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
bpf_pid_task_storage_lookup_elem(struct bpf_map * map,void * key)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
bpf_pid_task_storage_update_elem(struct bpf_map * map,void * key,void * value,u64 map_flags)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
task_storage_delete(struct task_struct * task,struct bpf_map * map)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
bpf_pid_task_storage_delete_elem(struct bpf_map * map,void * key)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
BPF_CALL_4(bpf_task_storage_get,struct bpf_map *,map,struct task_struct *,task,void *,value,u64,flags)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
BPF_CALL_2(bpf_task_storage_delete,struct bpf_map *,map,struct task_struct *,task)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
notsupp_get_next_key(struct bpf_map * map,void * key,void * next_key)278 static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
279 {
280 return -ENOTSUPP;
281 }
282
task_storage_map_alloc(union bpf_attr * attr)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
task_storage_map_free(struct bpf_map * map)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 const struct bpf_func_proto bpf_task_storage_get_proto = {
321 .func = bpf_task_storage_get,
322 .gpl_only = false,
323 .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
324 .arg1_type = ARG_CONST_MAP_PTR,
325 .arg2_type = ARG_PTR_TO_BTF_ID,
326 .arg2_btf_id = &btf_task_struct_ids[0],
327 .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
328 .arg4_type = ARG_ANYTHING,
329 };
330
331 const struct bpf_func_proto bpf_task_storage_delete_proto = {
332 .func = bpf_task_storage_delete,
333 .gpl_only = false,
334 .ret_type = RET_INTEGER,
335 .arg1_type = ARG_CONST_MAP_PTR,
336 .arg2_type = ARG_PTR_TO_BTF_ID,
337 .arg2_btf_id = &btf_task_struct_ids[0],
338 };
339