1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2019 Facebook
3
4 #include <stdint.h>
5 #include <stddef.h>
6 #include <stdbool.h>
7 #include <linux/bpf.h>
8 #include <linux/ptrace.h>
9 #include <linux/sched.h>
10 #include <linux/types.h>
11 #include <bpf/bpf_helpers.h>
12
13 typedef uint32_t pid_t;
14 struct task_struct {};
15
16 #define TASK_COMM_LEN 16
17 #define PERF_MAX_STACK_DEPTH 127
18
19 #define STROBE_TYPE_INVALID 0
20 #define STROBE_TYPE_INT 1
21 #define STROBE_TYPE_STR 2
22 #define STROBE_TYPE_MAP 3
23
24 #define STACK_TABLE_EPOCH_SHIFT 20
25 #define STROBE_MAX_STR_LEN 1
26 #define STROBE_MAX_CFGS 32
27 #define STROBE_MAX_PAYLOAD \
28 (STROBE_MAX_STRS * STROBE_MAX_STR_LEN + \
29 STROBE_MAX_MAPS * (1 + STROBE_MAX_MAP_ENTRIES * 2) * STROBE_MAX_STR_LEN)
30
31 struct strobe_value_header {
32 /*
33 * meaning depends on type:
34 * 1. int: 0, if value not set, 1 otherwise
35 * 2. str: 1 always, whether value is set or not is determined by ptr
36 * 3. map: 1 always, pointer points to additional struct with number
37 * of entries (up to STROBE_MAX_MAP_ENTRIES)
38 */
39 uint16_t len;
40 /*
41 * _reserved might be used for some future fields/flags, but we always
42 * want to keep strobe_value_header to be 8 bytes, so BPF can read 16
43 * bytes in one go and get both header and value
44 */
45 uint8_t _reserved[6];
46 };
47
48 /*
49 * strobe_value_generic is used from BPF probe only, but needs to be a union
50 * of strobe_value_int/strobe_value_str/strobe_value_map
51 */
52 struct strobe_value_generic {
53 struct strobe_value_header header;
54 union {
55 int64_t val;
56 void *ptr;
57 };
58 };
59
60 struct strobe_value_int {
61 struct strobe_value_header header;
62 int64_t value;
63 };
64
65 struct strobe_value_str {
66 struct strobe_value_header header;
67 const char* value;
68 };
69
70 struct strobe_value_map {
71 struct strobe_value_header header;
72 const struct strobe_map_raw* value;
73 };
74
75 struct strobe_map_entry {
76 const char* key;
77 const char* val;
78 };
79
80 /*
81 * Map of C-string key/value pairs with fixed maximum capacity. Each map has
82 * corresponding int64 ID, which application can use (or ignore) in whatever
83 * way appropriate. Map is "write-only", there is no way to get data out of
84 * map. Map is intended to be used to provide metadata for profilers and is
85 * not to be used for internal in-app communication. All methods are
86 * thread-safe.
87 */
88 struct strobe_map_raw {
89 /*
90 * general purpose unique ID that's up to application to decide
91 * whether and how to use; for request metadata use case id is unique
92 * request ID that's used to match metadata with stack traces on
93 * Strobelight backend side
94 */
95 int64_t id;
96 /* number of used entries in map */
97 int64_t cnt;
98 /*
99 * having volatile doesn't change anything on BPF side, but clang
100 * emits warnings for passing `volatile const char *` into
101 * bpf_probe_read_user_str that expects just `const char *`
102 */
103 const char* tag;
104 /*
105 * key/value entries, each consisting of 2 pointers to key and value
106 * C strings
107 */
108 struct strobe_map_entry entries[STROBE_MAX_MAP_ENTRIES];
109 };
110
111 /* Following values define supported values of TLS mode */
112 #define TLS_NOT_SET -1
113 #define TLS_LOCAL_EXEC 0
114 #define TLS_IMM_EXEC 1
115 #define TLS_GENERAL_DYN 2
116
117 /*
118 * structure that universally represents TLS location (both for static
119 * executables and shared libraries)
120 */
121 struct strobe_value_loc {
122 /*
123 * tls_mode defines what TLS mode was used for particular metavariable:
124 * - -1 (TLS_NOT_SET) - no metavariable;
125 * - 0 (TLS_LOCAL_EXEC) - Local Executable mode;
126 * - 1 (TLS_IMM_EXEC) - Immediate Executable mode;
127 * - 2 (TLS_GENERAL_DYN) - General Dynamic mode;
128 * Local Dynamic mode is not yet supported, because never seen in
129 * practice. Mode defines how offset field is interpreted. See
130 * calc_location() in below for details.
131 */
132 int64_t tls_mode;
133 /*
134 * TLS_LOCAL_EXEC: offset from thread pointer (fs:0 for x86-64,
135 * tpidr_el0 for aarch64).
136 * TLS_IMM_EXEC: absolute address of GOT entry containing offset
137 * from thread pointer;
138 * TLS_GENERAL_DYN: absolute addres of double GOT entry
139 * containing tls_index_t struct;
140 */
141 int64_t offset;
142 };
143
144 struct strobemeta_cfg {
145 int64_t req_meta_idx;
146 struct strobe_value_loc int_locs[STROBE_MAX_INTS];
147 struct strobe_value_loc str_locs[STROBE_MAX_STRS];
148 struct strobe_value_loc map_locs[STROBE_MAX_MAPS];
149 };
150
151 struct strobe_map_descr {
152 uint64_t id;
153 int16_t tag_len;
154 /*
155 * cnt <0 - map value isn't set;
156 * 0 - map has id set, but no key/value entries
157 */
158 int16_t cnt;
159 /*
160 * both key_lens[i] and val_lens[i] should be >0 for present key/value
161 * entry
162 */
163 uint16_t key_lens[STROBE_MAX_MAP_ENTRIES];
164 uint16_t val_lens[STROBE_MAX_MAP_ENTRIES];
165 };
166
167 struct strobemeta_payload {
168 /* req_id has valid request ID, if req_meta_valid == 1 */
169 int64_t req_id;
170 uint8_t req_meta_valid;
171 /*
172 * mask has Nth bit set to 1, if Nth metavar was present and
173 * successfully read
174 */
175 uint64_t int_vals_set_mask;
176 int64_t int_vals[STROBE_MAX_INTS];
177 /* len is >0 for present values */
178 uint16_t str_lens[STROBE_MAX_STRS];
179 /* if map_descrs[i].cnt == -1, metavar is not present/set */
180 struct strobe_map_descr map_descrs[STROBE_MAX_MAPS];
181 /*
182 * payload has compactly packed values of str and map variables in the
183 * form: strval1\0strval2\0map1key1\0map1val1\0map2key1\0map2val1\0
184 * (and so on); str_lens[i], key_lens[i] and val_lens[i] determines
185 * value length
186 */
187 char payload[STROBE_MAX_PAYLOAD];
188 };
189
190 struct strobelight_bpf_sample {
191 uint64_t ktime;
192 char comm[TASK_COMM_LEN];
193 pid_t pid;
194 int user_stack_id;
195 int kernel_stack_id;
196 int has_meta;
197 struct strobemeta_payload metadata;
198 /*
199 * makes it possible to pass (<real payload size> + 1) as data size to
200 * perf_submit() to avoid perf_submit's paranoia about passing zero as
201 * size, as it deduces that <real payload size> might be
202 * **theoretically** zero
203 */
204 char dummy_safeguard;
205 };
206
207 struct {
208 __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
209 __uint(max_entries, 32);
210 __uint(key_size, sizeof(int));
211 __uint(value_size, sizeof(int));
212 } samples SEC(".maps");
213
214 struct {
215 __uint(type, BPF_MAP_TYPE_STACK_TRACE);
216 __uint(max_entries, 16);
217 __uint(key_size, sizeof(uint32_t));
218 __uint(value_size, sizeof(uint64_t) * PERF_MAX_STACK_DEPTH);
219 } stacks_0 SEC(".maps");
220
221 struct {
222 __uint(type, BPF_MAP_TYPE_STACK_TRACE);
223 __uint(max_entries, 16);
224 __uint(key_size, sizeof(uint32_t));
225 __uint(value_size, sizeof(uint64_t) * PERF_MAX_STACK_DEPTH);
226 } stacks_1 SEC(".maps");
227
228 struct {
229 __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
230 __uint(max_entries, 1);
231 __type(key, uint32_t);
232 __type(value, struct strobelight_bpf_sample);
233 } sample_heap SEC(".maps");
234
235 struct {
236 __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
237 __uint(max_entries, STROBE_MAX_CFGS);
238 __type(key, pid_t);
239 __type(value, struct strobemeta_cfg);
240 } strobemeta_cfgs SEC(".maps");
241
242 /* Type for the dtv. */
243 /* https://github.com/lattera/glibc/blob/master/nptl/sysdeps/x86_64/tls.h#L34 */
244 typedef union dtv {
245 size_t counter;
246 struct {
247 void* val;
248 bool is_static;
249 } pointer;
250 } dtv_t;
251
252 /* Partial definition for tcbhead_t */
253 /* https://github.com/bminor/glibc/blob/master/sysdeps/x86_64/nptl/tls.h#L42 */
254 struct tcbhead {
255 void* tcb;
256 dtv_t* dtv;
257 };
258
259 /*
260 * TLS module/offset information for shared library case.
261 * For x86-64, this is mapped onto two entries in GOT.
262 * For aarch64, this is pointed to by second GOT entry.
263 */
264 struct tls_index {
265 uint64_t module;
266 uint64_t offset;
267 };
268
269 #ifdef SUBPROGS
270 __noinline
271 #else
272 __always_inline
273 #endif
calc_location(struct strobe_value_loc * loc,void * tls_base)274 static void *calc_location(struct strobe_value_loc *loc, void *tls_base)
275 {
276 /*
277 * tls_mode value is:
278 * - -1 (TLS_NOT_SET), if no metavar is present;
279 * - 0 (TLS_LOCAL_EXEC), if metavar uses Local Executable mode of TLS
280 * (offset from fs:0 for x86-64 or tpidr_el0 for aarch64);
281 * - 1 (TLS_IMM_EXEC), if metavar uses Immediate Executable mode of TLS;
282 * - 2 (TLS_GENERAL_DYN), if metavar uses General Dynamic mode of TLS;
283 * This schema allows to use something like:
284 * (tls_mode + 1) * (tls_base + offset)
285 * to get NULL for "no metavar" location, or correct pointer for local
286 * executable mode without doing extra ifs.
287 */
288 if (loc->tls_mode <= TLS_LOCAL_EXEC) {
289 /* static executable is simple, we just have offset from
290 * tls_base */
291 void *addr = tls_base + loc->offset;
292 /* multiply by (tls_mode + 1) to get NULL, if we have no
293 * metavar in this slot */
294 return (void *)((loc->tls_mode + 1) * (int64_t)addr);
295 }
296 /*
297 * Other modes are more complicated, we need to jump through few hoops.
298 *
299 * For immediate executable mode (currently supported only for aarch64):
300 * - loc->offset is pointing to a GOT entry containing fixed offset
301 * relative to tls_base;
302 *
303 * For general dynamic mode:
304 * - loc->offset is pointing to a beginning of double GOT entries;
305 * - (for aarch64 only) second entry points to tls_index_t struct;
306 * - (for x86-64 only) two GOT entries are already tls_index_t;
307 * - tls_index_t->module is used to find start of TLS section in
308 * which variable resides;
309 * - tls_index_t->offset provides offset within that TLS section,
310 * pointing to value of variable.
311 */
312 struct tls_index tls_index;
313 dtv_t *dtv;
314 void *tls_ptr;
315
316 bpf_probe_read_user(&tls_index, sizeof(struct tls_index),
317 (void *)loc->offset);
318 /* valid module index is always positive */
319 if (tls_index.module > 0) {
320 /* dtv = ((struct tcbhead *)tls_base)->dtv[tls_index.module] */
321 bpf_probe_read_user(&dtv, sizeof(dtv),
322 &((struct tcbhead *)tls_base)->dtv);
323 dtv += tls_index.module;
324 } else {
325 dtv = NULL;
326 }
327 bpf_probe_read_user(&tls_ptr, sizeof(void *), dtv);
328 /* if pointer has (void *)-1 value, then TLS wasn't initialized yet */
329 return tls_ptr && tls_ptr != (void *)-1
330 ? tls_ptr + tls_index.offset
331 : NULL;
332 }
333
334 #ifdef SUBPROGS
335 __noinline
336 #else
337 __always_inline
338 #endif
read_int_var(struct strobemeta_cfg * cfg,size_t idx,void * tls_base,struct strobe_value_generic * value,struct strobemeta_payload * data)339 static void read_int_var(struct strobemeta_cfg *cfg,
340 size_t idx, void *tls_base,
341 struct strobe_value_generic *value,
342 struct strobemeta_payload *data)
343 {
344 void *location = calc_location(&cfg->int_locs[idx], tls_base);
345 if (!location)
346 return;
347
348 bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
349 data->int_vals[idx] = value->val;
350 if (value->header.len)
351 data->int_vals_set_mask |= (1 << idx);
352 }
353
read_str_var(struct strobemeta_cfg * cfg,size_t idx,void * tls_base,struct strobe_value_generic * value,struct strobemeta_payload * data,void * payload)354 static __always_inline uint64_t read_str_var(struct strobemeta_cfg *cfg,
355 size_t idx, void *tls_base,
356 struct strobe_value_generic *value,
357 struct strobemeta_payload *data,
358 void *payload)
359 {
360 void *location;
361 uint64_t len;
362
363 data->str_lens[idx] = 0;
364 location = calc_location(&cfg->str_locs[idx], tls_base);
365 if (!location)
366 return 0;
367
368 bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
369 len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN, value->ptr);
370 /*
371 * if bpf_probe_read_user_str returns error (<0), due to casting to
372 * unsinged int, it will become big number, so next check is
373 * sufficient to check for errors AND prove to BPF verifier, that
374 * bpf_probe_read_user_str won't return anything bigger than
375 * STROBE_MAX_STR_LEN
376 */
377 if (len > STROBE_MAX_STR_LEN)
378 return 0;
379
380 data->str_lens[idx] = len;
381 return len;
382 }
383
read_map_var(struct strobemeta_cfg * cfg,size_t idx,void * tls_base,struct strobe_value_generic * value,struct strobemeta_payload * data,void * payload)384 static __always_inline void *read_map_var(struct strobemeta_cfg *cfg,
385 size_t idx, void *tls_base,
386 struct strobe_value_generic *value,
387 struct strobemeta_payload *data,
388 void *payload)
389 {
390 struct strobe_map_descr* descr = &data->map_descrs[idx];
391 struct strobe_map_raw map;
392 void *location;
393 uint64_t len;
394 int i;
395
396 descr->tag_len = 0; /* presume no tag is set */
397 descr->cnt = -1; /* presume no value is set */
398
399 location = calc_location(&cfg->map_locs[idx], tls_base);
400 if (!location)
401 return payload;
402
403 bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
404 if (bpf_probe_read_user(&map, sizeof(struct strobe_map_raw), value->ptr))
405 return payload;
406
407 descr->id = map.id;
408 descr->cnt = map.cnt;
409 if (cfg->req_meta_idx == idx) {
410 data->req_id = map.id;
411 data->req_meta_valid = 1;
412 }
413
414 len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN, map.tag);
415 if (len <= STROBE_MAX_STR_LEN) {
416 descr->tag_len = len;
417 payload += len;
418 }
419
420 #ifdef NO_UNROLL
421 #pragma clang loop unroll(disable)
422 #else
423 #pragma unroll
424 #endif
425 for (int i = 0; i < STROBE_MAX_MAP_ENTRIES; ++i) {
426 if (i >= map.cnt)
427 break;
428
429 descr->key_lens[i] = 0;
430 len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN,
431 map.entries[i].key);
432 if (len <= STROBE_MAX_STR_LEN) {
433 descr->key_lens[i] = len;
434 payload += len;
435 }
436 descr->val_lens[i] = 0;
437 len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN,
438 map.entries[i].val);
439 if (len <= STROBE_MAX_STR_LEN) {
440 descr->val_lens[i] = len;
441 payload += len;
442 }
443 }
444
445 return payload;
446 }
447
448 #ifdef USE_BPF_LOOP
449 enum read_type {
450 READ_INT_VAR,
451 READ_MAP_VAR,
452 READ_STR_VAR,
453 };
454
455 struct read_var_ctx {
456 struct strobemeta_payload *data;
457 void *tls_base;
458 struct strobemeta_cfg *cfg;
459 void *payload;
460 /* value gets mutated */
461 struct strobe_value_generic *value;
462 enum read_type type;
463 };
464
read_var_callback(__u32 index,struct read_var_ctx * ctx)465 static int read_var_callback(__u32 index, struct read_var_ctx *ctx)
466 {
467 switch (ctx->type) {
468 case READ_INT_VAR:
469 if (index >= STROBE_MAX_INTS)
470 return 1;
471 read_int_var(ctx->cfg, index, ctx->tls_base, ctx->value, ctx->data);
472 break;
473 case READ_MAP_VAR:
474 if (index >= STROBE_MAX_MAPS)
475 return 1;
476 ctx->payload = read_map_var(ctx->cfg, index, ctx->tls_base,
477 ctx->value, ctx->data, ctx->payload);
478 break;
479 case READ_STR_VAR:
480 if (index >= STROBE_MAX_STRS)
481 return 1;
482 ctx->payload += read_str_var(ctx->cfg, index, ctx->tls_base,
483 ctx->value, ctx->data, ctx->payload);
484 break;
485 }
486 return 0;
487 }
488 #endif /* USE_BPF_LOOP */
489
490 /*
491 * read_strobe_meta returns NULL, if no metadata was read; otherwise returns
492 * pointer to *right after* payload ends
493 */
494 #ifdef SUBPROGS
495 __noinline
496 #else
497 __always_inline
498 #endif
read_strobe_meta(struct task_struct * task,struct strobemeta_payload * data)499 static void *read_strobe_meta(struct task_struct *task,
500 struct strobemeta_payload *data)
501 {
502 pid_t pid = bpf_get_current_pid_tgid() >> 32;
503 struct strobe_value_generic value = {0};
504 struct strobemeta_cfg *cfg;
505 void *tls_base, *payload;
506
507 cfg = bpf_map_lookup_elem(&strobemeta_cfgs, &pid);
508 if (!cfg)
509 return NULL;
510
511 data->int_vals_set_mask = 0;
512 data->req_meta_valid = 0;
513 payload = data->payload;
514 /*
515 * we don't have struct task_struct definition, it should be:
516 * tls_base = (void *)task->thread.fsbase;
517 */
518 tls_base = (void *)task;
519
520 #ifdef USE_BPF_LOOP
521 struct read_var_ctx ctx = {
522 .cfg = cfg,
523 .tls_base = tls_base,
524 .value = &value,
525 .data = data,
526 .payload = payload,
527 };
528 int err;
529
530 ctx.type = READ_INT_VAR;
531 err = bpf_loop(STROBE_MAX_INTS, read_var_callback, &ctx, 0);
532 if (err != STROBE_MAX_INTS)
533 return NULL;
534
535 ctx.type = READ_STR_VAR;
536 err = bpf_loop(STROBE_MAX_STRS, read_var_callback, &ctx, 0);
537 if (err != STROBE_MAX_STRS)
538 return NULL;
539
540 ctx.type = READ_MAP_VAR;
541 err = bpf_loop(STROBE_MAX_MAPS, read_var_callback, &ctx, 0);
542 if (err != STROBE_MAX_MAPS)
543 return NULL;
544 #else
545 #ifdef NO_UNROLL
546 #pragma clang loop unroll(disable)
547 #else
548 #pragma unroll
549 #endif /* NO_UNROLL */
550 for (int i = 0; i < STROBE_MAX_INTS; ++i) {
551 read_int_var(cfg, i, tls_base, &value, data);
552 }
553 #ifdef NO_UNROLL
554 #pragma clang loop unroll(disable)
555 #else
556 #pragma unroll
557 #endif /* NO_UNROLL */
558 for (int i = 0; i < STROBE_MAX_STRS; ++i) {
559 payload += read_str_var(cfg, i, tls_base, &value, data, payload);
560 }
561 #ifdef NO_UNROLL
562 #pragma clang loop unroll(disable)
563 #else
564 #pragma unroll
565 #endif /* NO_UNROLL */
566 for (int i = 0; i < STROBE_MAX_MAPS; ++i) {
567 payload = read_map_var(cfg, i, tls_base, &value, data, payload);
568 }
569 #endif /* USE_BPF_LOOP */
570
571 /*
572 * return pointer right after end of payload, so it's possible to
573 * calculate exact amount of useful data that needs to be sent
574 */
575 return payload;
576 }
577
578 SEC("raw_tracepoint/kfree_skb")
on_event(struct pt_regs * ctx)579 int on_event(struct pt_regs *ctx) {
580 pid_t pid = bpf_get_current_pid_tgid() >> 32;
581 struct strobelight_bpf_sample* sample;
582 struct task_struct *task;
583 uint32_t zero = 0;
584 uint64_t ktime_ns;
585 void *sample_end;
586
587 sample = bpf_map_lookup_elem(&sample_heap, &zero);
588 if (!sample)
589 return 0; /* this will never happen */
590
591 sample->pid = pid;
592 bpf_get_current_comm(&sample->comm, TASK_COMM_LEN);
593 ktime_ns = bpf_ktime_get_ns();
594 sample->ktime = ktime_ns;
595
596 task = (struct task_struct *)bpf_get_current_task();
597 sample_end = read_strobe_meta(task, &sample->metadata);
598 sample->has_meta = sample_end != NULL;
599 sample_end = sample_end ? : &sample->metadata;
600
601 if ((ktime_ns >> STACK_TABLE_EPOCH_SHIFT) & 1) {
602 sample->kernel_stack_id = bpf_get_stackid(ctx, &stacks_1, 0);
603 sample->user_stack_id = bpf_get_stackid(ctx, &stacks_1, BPF_F_USER_STACK);
604 } else {
605 sample->kernel_stack_id = bpf_get_stackid(ctx, &stacks_0, 0);
606 sample->user_stack_id = bpf_get_stackid(ctx, &stacks_0, BPF_F_USER_STACK);
607 }
608
609 uint64_t sample_size = sample_end - (void *)sample;
610 /* should always be true */
611 if (sample_size < sizeof(struct strobelight_bpf_sample))
612 bpf_perf_event_output(ctx, &samples, 0, sample, 1 + sample_size);
613 return 0;
614 }
615
616 char _license[] SEC("license") = "GPL";
617