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
bpf_task_storage_lock(void)26 static void bpf_task_storage_lock(void)
27 {
28 migrate_disable();
29 this_cpu_inc(bpf_task_storage_busy);
30 }
31
bpf_task_storage_unlock(void)32 static void bpf_task_storage_unlock(void)
33 {
34 this_cpu_dec(bpf_task_storage_busy);
35 migrate_enable();
36 }
37
bpf_task_storage_trylock(void)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
task_storage_ptr(void * owner)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 *
task_storage_lookup(struct task_struct * task,struct bpf_map * map,bool cacheit_lockit)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
bpf_task_storage_free(struct task_struct * task)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
bpf_pid_task_storage_lookup_elem(struct bpf_map * map,void * key)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
bpf_pid_task_storage_update_elem(struct bpf_map * map,void * key,void * value,u64 map_flags)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
task_storage_delete(struct task_struct * task,struct bpf_map * map)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
bpf_pid_task_storage_delete_elem(struct bpf_map * map,void * key)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 */
BPF_CALL_5(bpf_task_storage_get,struct bpf_map *,map,struct task_struct *,task,void *,value,u64,flags,gfp_t,gfp_flags)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
BPF_CALL_2(bpf_task_storage_delete,struct bpf_map *,map,struct task_struct *,task)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
notsupp_get_next_key(struct bpf_map * map,void * key,void * next_key)284 static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
285 {
286 return -ENOTSUPP;
287 }
288
task_storage_map_alloc(union bpf_attr * attr)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
task_storage_map_free(struct bpf_map * map)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 };
344