xref: /openbmc/linux/kernel/bpf/bpf_task_storage.c (revision 91571a51)
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 *local_storage;
75 
76 	rcu_read_lock();
77 
78 	local_storage = rcu_dereference(task->bpf_storage);
79 	if (!local_storage) {
80 		rcu_read_unlock();
81 		return;
82 	}
83 
84 	bpf_task_storage_lock();
85 	bpf_local_storage_destroy(local_storage);
86 	bpf_task_storage_unlock();
87 	rcu_read_unlock();
88 }
89 
bpf_pid_task_storage_lookup_elem(struct bpf_map * map,void * key)90 static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key)
91 {
92 	struct bpf_local_storage_data *sdata;
93 	struct task_struct *task;
94 	unsigned int f_flags;
95 	struct pid *pid;
96 	int fd, err;
97 
98 	fd = *(int *)key;
99 	pid = pidfd_get_pid(fd, &f_flags);
100 	if (IS_ERR(pid))
101 		return ERR_CAST(pid);
102 
103 	/* We should be in an RCU read side critical section, it should be safe
104 	 * to call pid_task.
105 	 */
106 	WARN_ON_ONCE(!rcu_read_lock_held());
107 	task = pid_task(pid, PIDTYPE_PID);
108 	if (!task) {
109 		err = -ENOENT;
110 		goto out;
111 	}
112 
113 	bpf_task_storage_lock();
114 	sdata = task_storage_lookup(task, map, true);
115 	bpf_task_storage_unlock();
116 	put_pid(pid);
117 	return sdata ? sdata->data : NULL;
118 out:
119 	put_pid(pid);
120 	return ERR_PTR(err);
121 }
122 
bpf_pid_task_storage_update_elem(struct bpf_map * map,void * key,void * value,u64 map_flags)123 static long bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
124 					     void *value, u64 map_flags)
125 {
126 	struct bpf_local_storage_data *sdata;
127 	struct task_struct *task;
128 	unsigned int f_flags;
129 	struct pid *pid;
130 	int fd, err;
131 
132 	fd = *(int *)key;
133 	pid = pidfd_get_pid(fd, &f_flags);
134 	if (IS_ERR(pid))
135 		return PTR_ERR(pid);
136 
137 	/* We should be in an RCU read side critical section, it should be safe
138 	 * to call pid_task.
139 	 */
140 	WARN_ON_ONCE(!rcu_read_lock_held());
141 	task = pid_task(pid, PIDTYPE_PID);
142 	if (!task) {
143 		err = -ENOENT;
144 		goto out;
145 	}
146 
147 	bpf_task_storage_lock();
148 	sdata = bpf_local_storage_update(
149 		task, (struct bpf_local_storage_map *)map, value, map_flags,
150 		GFP_ATOMIC);
151 	bpf_task_storage_unlock();
152 
153 	err = PTR_ERR_OR_ZERO(sdata);
154 out:
155 	put_pid(pid);
156 	return err;
157 }
158 
task_storage_delete(struct task_struct * task,struct bpf_map * map,bool nobusy)159 static int task_storage_delete(struct task_struct *task, struct bpf_map *map,
160 			       bool nobusy)
161 {
162 	struct bpf_local_storage_data *sdata;
163 
164 	sdata = task_storage_lookup(task, map, false);
165 	if (!sdata)
166 		return -ENOENT;
167 
168 	if (!nobusy)
169 		return -EBUSY;
170 
171 	bpf_selem_unlink(SELEM(sdata), false);
172 
173 	return 0;
174 }
175 
bpf_pid_task_storage_delete_elem(struct bpf_map * map,void * key)176 static long bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
177 {
178 	struct task_struct *task;
179 	unsigned int f_flags;
180 	struct pid *pid;
181 	int fd, err;
182 
183 	fd = *(int *)key;
184 	pid = pidfd_get_pid(fd, &f_flags);
185 	if (IS_ERR(pid))
186 		return PTR_ERR(pid);
187 
188 	/* We should be in an RCU read side critical section, it should be safe
189 	 * to call pid_task.
190 	 */
191 	WARN_ON_ONCE(!rcu_read_lock_held());
192 	task = pid_task(pid, PIDTYPE_PID);
193 	if (!task) {
194 		err = -ENOENT;
195 		goto out;
196 	}
197 
198 	bpf_task_storage_lock();
199 	err = task_storage_delete(task, map, true);
200 	bpf_task_storage_unlock();
201 out:
202 	put_pid(pid);
203 	return err;
204 }
205 
206 /* Called by bpf_task_storage_get*() helpers */
__bpf_task_storage_get(struct bpf_map * map,struct task_struct * task,void * value,u64 flags,gfp_t gfp_flags,bool nobusy)207 static void *__bpf_task_storage_get(struct bpf_map *map,
208 				    struct task_struct *task, void *value,
209 				    u64 flags, gfp_t gfp_flags, bool nobusy)
210 {
211 	struct bpf_local_storage_data *sdata;
212 
213 	sdata = task_storage_lookup(task, map, nobusy);
214 	if (sdata)
215 		return sdata->data;
216 
217 	/* only allocate new storage, when the task is refcounted */
218 	if (refcount_read(&task->usage) &&
219 	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) && nobusy) {
220 		sdata = bpf_local_storage_update(
221 			task, (struct bpf_local_storage_map *)map, value,
222 			BPF_NOEXIST, gfp_flags);
223 		return IS_ERR(sdata) ? NULL : sdata->data;
224 	}
225 
226 	return NULL;
227 }
228 
229 /* *gfp_flags* is a hidden argument provided by the verifier */
BPF_CALL_5(bpf_task_storage_get_recur,struct bpf_map *,map,struct task_struct *,task,void *,value,u64,flags,gfp_t,gfp_flags)230 BPF_CALL_5(bpf_task_storage_get_recur, struct bpf_map *, map, struct task_struct *,
231 	   task, void *, value, u64, flags, gfp_t, gfp_flags)
232 {
233 	bool nobusy;
234 	void *data;
235 
236 	WARN_ON_ONCE(!bpf_rcu_lock_held());
237 	if (flags & ~BPF_LOCAL_STORAGE_GET_F_CREATE || !task)
238 		return (unsigned long)NULL;
239 
240 	nobusy = bpf_task_storage_trylock();
241 	data = __bpf_task_storage_get(map, task, value, flags,
242 				      gfp_flags, nobusy);
243 	if (nobusy)
244 		bpf_task_storage_unlock();
245 	return (unsigned long)data;
246 }
247 
248 /* *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)249 BPF_CALL_5(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
250 	   task, void *, value, u64, flags, gfp_t, gfp_flags)
251 {
252 	void *data;
253 
254 	WARN_ON_ONCE(!bpf_rcu_lock_held());
255 	if (flags & ~BPF_LOCAL_STORAGE_GET_F_CREATE || !task)
256 		return (unsigned long)NULL;
257 
258 	bpf_task_storage_lock();
259 	data = __bpf_task_storage_get(map, task, value, flags,
260 				      gfp_flags, true);
261 	bpf_task_storage_unlock();
262 	return (unsigned long)data;
263 }
264 
BPF_CALL_2(bpf_task_storage_delete_recur,struct bpf_map *,map,struct task_struct *,task)265 BPF_CALL_2(bpf_task_storage_delete_recur, struct bpf_map *, map, struct task_struct *,
266 	   task)
267 {
268 	bool nobusy;
269 	int ret;
270 
271 	WARN_ON_ONCE(!bpf_rcu_lock_held());
272 	if (!task)
273 		return -EINVAL;
274 
275 	nobusy = bpf_task_storage_trylock();
276 	/* This helper must only be called from places where the lifetime of the task
277 	 * is guaranteed. Either by being refcounted or by being protected
278 	 * by an RCU read-side critical section.
279 	 */
280 	ret = task_storage_delete(task, map, nobusy);
281 	if (nobusy)
282 		bpf_task_storage_unlock();
283 	return ret;
284 }
285 
BPF_CALL_2(bpf_task_storage_delete,struct bpf_map *,map,struct task_struct *,task)286 BPF_CALL_2(bpf_task_storage_delete, struct bpf_map *, map, struct task_struct *,
287 	   task)
288 {
289 	int ret;
290 
291 	WARN_ON_ONCE(!bpf_rcu_lock_held());
292 	if (!task)
293 		return -EINVAL;
294 
295 	bpf_task_storage_lock();
296 	/* This helper must only be called from places where the lifetime of the task
297 	 * is guaranteed. Either by being refcounted or by being protected
298 	 * by an RCU read-side critical section.
299 	 */
300 	ret = task_storage_delete(task, map, true);
301 	bpf_task_storage_unlock();
302 	return ret;
303 }
304 
notsupp_get_next_key(struct bpf_map * map,void * key,void * next_key)305 static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
306 {
307 	return -ENOTSUPP;
308 }
309 
task_storage_map_alloc(union bpf_attr * attr)310 static struct bpf_map *task_storage_map_alloc(union bpf_attr *attr)
311 {
312 	return bpf_local_storage_map_alloc(attr, &task_cache, true);
313 }
314 
task_storage_map_free(struct bpf_map * map)315 static void task_storage_map_free(struct bpf_map *map)
316 {
317 	bpf_local_storage_map_free(map, &task_cache, &bpf_task_storage_busy);
318 }
319 
320 BTF_ID_LIST_GLOBAL_SINGLE(bpf_local_storage_map_btf_id, struct, bpf_local_storage_map)
321 const struct bpf_map_ops task_storage_map_ops = {
322 	.map_meta_equal = bpf_map_meta_equal,
323 	.map_alloc_check = bpf_local_storage_map_alloc_check,
324 	.map_alloc = task_storage_map_alloc,
325 	.map_free = task_storage_map_free,
326 	.map_get_next_key = notsupp_get_next_key,
327 	.map_lookup_elem = bpf_pid_task_storage_lookup_elem,
328 	.map_update_elem = bpf_pid_task_storage_update_elem,
329 	.map_delete_elem = bpf_pid_task_storage_delete_elem,
330 	.map_check_btf = bpf_local_storage_map_check_btf,
331 	.map_mem_usage = bpf_local_storage_map_mem_usage,
332 	.map_btf_id = &bpf_local_storage_map_btf_id[0],
333 	.map_owner_storage_ptr = task_storage_ptr,
334 };
335 
336 const struct bpf_func_proto bpf_task_storage_get_recur_proto = {
337 	.func = bpf_task_storage_get_recur,
338 	.gpl_only = false,
339 	.ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
340 	.arg1_type = ARG_CONST_MAP_PTR,
341 	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
342 	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
343 	.arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
344 	.arg4_type = ARG_ANYTHING,
345 };
346 
347 const struct bpf_func_proto bpf_task_storage_get_proto = {
348 	.func = bpf_task_storage_get,
349 	.gpl_only = false,
350 	.ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
351 	.arg1_type = ARG_CONST_MAP_PTR,
352 	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
353 	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
354 	.arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
355 	.arg4_type = ARG_ANYTHING,
356 };
357 
358 const struct bpf_func_proto bpf_task_storage_delete_recur_proto = {
359 	.func = bpf_task_storage_delete_recur,
360 	.gpl_only = false,
361 	.ret_type = RET_INTEGER,
362 	.arg1_type = ARG_CONST_MAP_PTR,
363 	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
364 	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
365 };
366 
367 const struct bpf_func_proto bpf_task_storage_delete_proto = {
368 	.func = bpf_task_storage_delete,
369 	.gpl_only = false,
370 	.ret_type = RET_INTEGER,
371 	.arg1_type = ARG_CONST_MAP_PTR,
372 	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
373 	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
374 };
375