summaryrefslogtreecommitdiffstats
path: root/tools/perf/util/bpf-prologue.c
blob: 77e4891e17b0aa9ef2492d70fe77209a7d28439a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
// SPDX-License-Identifier: GPL-2.0
/*
 * bpf-prologue.c
 *
 * Copyright (C) 2015 He Kuang <hekuang@huawei.com>
 * Copyright (C) 2015 Wang Nan <wangnan0@huawei.com>
 * Copyright (C) 2015 Huawei Inc.
 */

#include <bpf/libbpf.h>
#include "perf.h"
#include "debug.h"
#include "bpf-loader.h"
#include "bpf-prologue.h"
#include "probe-finder.h"
#include <errno.h>
#include <dwarf-regs.h>
#include <linux/filter.h>

#define BPF_REG_SIZE		8

#define JMP_TO_ERROR_CODE	-1
#define JMP_TO_SUCCESS_CODE	-2
#define JMP_TO_USER_CODE	-3

struct bpf_insn_pos {
	struct bpf_insn *begin;
	struct bpf_insn *end;
	struct bpf_insn *pos;
};

static inline int
pos_get_cnt(struct bpf_insn_pos *pos)
{
	return pos->pos - pos->begin;
}

static int
append_insn(struct bpf_insn new_insn, struct bpf_insn_pos *pos)
{
	if (!pos->pos)
		return -BPF_LOADER_ERRNO__PROLOGUE2BIG;

	if (pos->pos + 1 >= pos->end) {
		pr_err("bpf prologue: prologue too long\n");
		pos->pos = NULL;
		return -BPF_LOADER_ERRNO__PROLOGUE2BIG;
	}

	*(pos->pos)++ = new_insn;
	return 0;
}

static int
check_pos(struct bpf_insn_pos *pos)
{
	if (!pos->pos || pos->pos >= pos->end)
		return -BPF_LOADER_ERRNO__PROLOGUE2BIG;
	return 0;
}

/*
 * Convert type string (u8/u16/u32/u64/s8/s16/s32/s64 ..., see
 * Documentation/trace/kprobetrace.rst) to size field of BPF_LDX_MEM
 * instruction (BPF_{B,H,W,DW}).
 */
static int
argtype_to_ldx_size(const char *type)
{
	int arg_size = type ? atoi(&type[1]) : 64;

	switch (arg_size) {
	case 8:
		return BPF_B;
	case 16:
		return BPF_H;
	case 32:
		return BPF_W;
	case 64:
	default:
		return BPF_DW;
	}
}

static const char *
insn_sz_to_str(int insn_sz)
{
	switch (insn_sz) {
	case BPF_B:
		return "BPF_B";
	case BPF_H:
		return "BPF_H";
	case BPF_W:
		return "BPF_W";
	case BPF_DW:
		return "BPF_DW";
	default:
		return "UNKNOWN";
	}
}

/* Give it a shorter name */
#define ins(i, p) append_insn((i), (p))

/*
 * Give a register name (in 'reg'), generate instruction to
 * load register into an eBPF register rd:
 *   'ldd target_reg, offset(ctx_reg)', where:
 * ctx_reg is pre initialized to pointer of 'struct pt_regs'.
 */
static int
gen_ldx_reg_from_ctx(struct bpf_insn_pos *pos, int ctx_reg,
		     const char *reg, int target_reg)
{
	int offset = regs_query_register_offset(reg);

	if (offset < 0) {
		pr_err("bpf: prologue: failed to get register %s\n",
		       reg);
		return offset;
	}
	ins(BPF_LDX_MEM(BPF_DW, target_reg, ctx_reg, offset), pos);

	return check_pos(pos);
}

/*
 * Generate a BPF_FUNC_probe_read function call.
 *
 * src_base_addr_reg is a register holding base address,
 * dst_addr_reg is a register holding dest address (on stack),
 * result is:
 *
 *  *[dst_addr_reg] = *([src_base_addr_reg] + offset)
 *
 * Arguments of BPF_FUNC_probe_read:
 *     ARG1: ptr to stack (dest)
 *     ARG2: size (8)
 *     ARG3: unsafe ptr (src)
 */
static int
gen_read_mem(struct bpf_insn_pos *pos,
	     int src_base_addr_reg,
	     int dst_addr_reg,
	     long offset)
{
	/* mov arg3, src_base_addr_reg */
	if (src_base_addr_reg != BPF_REG_ARG3)
		ins(BPF_MOV64_REG(BPF_REG_ARG3, src_base_addr_reg), pos);
	/* add arg3, #offset */
	if (offset)
		ins(BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG3, offset), pos);

	/* mov arg2, #reg_size */
	ins(BPF_ALU64_IMM(BPF_MOV, BPF_REG_ARG2, BPF_REG_SIZE), pos);

	/* mov arg1, dst_addr_reg */
	if (dst_addr_reg != BPF_REG_ARG1)
		ins(BPF_MOV64_REG(BPF_REG_ARG1, dst_addr_reg), pos);

	/* Call probe_read  */
	ins(BPF_EMIT_CALL(BPF_FUNC_probe_read), pos);
	/*
	 * Error processing: if read fail, goto error code,
	 * will be relocated. Target should be the start of
	 * error processing code.
	 */
	ins(BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, JMP_TO_ERROR_CODE),
	    pos);

	return check_pos(pos);
}

/*
 * Each arg should be bare register. Fetch and save them into argument
 * registers (r3 - r5).
 *
 * BPF_REG_1 should have been initialized with pointer to
 * 'struct pt_regs'.
 */
static int
gen_prologue_fastpath(struct bpf_insn_pos *pos,
		      struct probe_trace_arg *args, int nargs)
{
	int i, err = 0;

	for (i = 0; i < nargs; i++) {
		err = gen_ldx_reg_from_ctx(pos, BPF_REG_1, args[i].value,
					   BPF_PROLOGUE_START_ARG_REG + i);
		if (err)
			goto errout;
	}

	return check_pos(pos);
errout:
	return err;
}

/*
 * Slow path:
 *   At least one argument has the form of 'offset($rx)'.
 *
 * Following code first stores them into stack, then loads all of then
 * to r2 - r5.
 * Before final loading, the final result should be:
 *
 * low address
 * BPF_REG_FP - 24  ARG3
 * BPF_REG_FP - 16  ARG2
 * BPF_REG_FP - 8   ARG1
 * BPF_REG_FP
 * high address
 *
 * For each argument (described as: offn(...off2(off1(reg)))),
 * generates following code:
 *
 *  r7 <- fp
 *  r7 <- r7 - stack_offset  // Ideal code should initialize r7 using
 *                           // fp before generating args. However,
 *                           // eBPF won't regard r7 as stack pointer
 *                           // if it is generated by minus 8 from
 *                           // another stack pointer except fp.
 *                           // This is why we have to set r7
 *                           // to fp for each variable.
 *  r3 <- value of 'reg'-> generated using gen_ldx_reg_from_ctx()
 *  (r7) <- r3       // skip following instructions for bare reg
 *  r3 <- r3 + off1  . // skip if off1 == 0
 *  r2 <- 8           \
 *  r1 <- r7           |-> generated by gen_read_mem()
 *  call probe_read    /
 *  jnei r0, 0, err  ./
 *  r3 <- (r7)
 *  r3 <- r3 + off2  . // skip if off2 == 0
 *  r2 <- 8           \  // r2 may be broken by probe_read, so set again
 *  r1 <- r7           |-> generated by gen_read_mem()
 *  call probe_read    /
 *  jnei r0, 0, err  ./
 *  ...
 */
static int
gen_prologue_slowpath(struct bpf_insn_pos *pos,
		      struct probe_trace_arg *args, int nargs)
{
	int err, i;

	for (i = 0; i < nargs; i++) {
		struct probe_trace_arg *arg = &args[i];
		const char *reg = arg->value;
		struct probe_trace_arg_ref *ref = NULL;
		int stack_offset = (i + 1) * -8;

		pr_debug("prologue: fetch arg %d, base reg is %s\n",
			 i, reg);

		/* value of base register is stored into ARG3 */
		err = gen_ldx_reg_from_ctx(pos, BPF_REG_CTX, reg,
					   BPF_REG_ARG3);
		if (err) {
			pr_err("prologue: failed to get offset of register %s\n",
			       reg);
			goto errout;
		}

		/* Make r7 the stack pointer. */
		ins(BPF_MOV64_REG(BPF_REG_7, BPF_REG_FP), pos);
		/* r7 += -8 */
		ins(BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, stack_offset), pos);
		/*
		 * Store r3 (base register) onto stack
		 * Ensure fp[offset] is set.
		 * fp is the only valid base register when storing
		 * into stack. We are not allowed to use r7 as base
		 * register here.
		 */
		ins(BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_ARG3,
				stack_offset), pos);

		ref = arg->ref;
		while (ref) {
			pr_debug("prologue: arg %d: offset %ld\n",
				 i, ref->offset);
			err = gen_read_mem(pos, BPF_REG_3, BPF_REG_7,
					   ref->offset);
			if (err) {
				pr_err("prologue: failed to generate probe_read function call\n");
				goto errout;
			}

			ref = ref->next;
			/*
			 * Load previous result into ARG3. Use
			 * BPF_REG_FP instead of r7 because verifier
			 * allows FP based addressing only.
			 */
			if (ref)
				ins(BPF_LDX_MEM(BPF_DW, BPF_REG_ARG3,
						BPF_REG_FP, stack_offset), pos);
		}
	}

	/* Final pass: read to registers */
	for (i = 0; i < nargs; i++) {
		int insn_sz = (args[i].ref) ? argtype_to_ldx_size(args[i].type) : BPF_DW;

		pr_debug("prologue: load arg %d, insn_sz is %s\n",
			 i, insn_sz_to_str(insn_sz));
		ins(BPF_LDX_MEM(insn_sz, BPF_PROLOGUE_START_ARG_REG + i,
				BPF_REG_FP, -BPF_REG_SIZE * (i + 1)), pos);
	}

	ins(BPF_JMP_IMM(BPF_JA, BPF_REG_0, 0, JMP_TO_SUCCESS_CODE), pos);

	return check_pos(pos);
errout:
	return err;
}

static int
prologue_relocate(struct bpf_insn_pos *pos, struct bpf_insn *error_code,
		  struct bpf_insn *success_code, struct bpf_insn *user_code)
{
	struct bpf_insn *insn;

	if (check_pos(pos))
		return -BPF_LOADER_ERRNO__PROLOGUE2BIG;

	for (insn = pos->begin; insn < pos->pos; insn++) {
		struct bpf_insn *target;
		u8 class = BPF_CLASS(insn->code);
		u8 opcode;

		if (class != BPF_JMP)
			continue;
		opcode = BPF_OP(insn->code);
		if (opcode == BPF_CALL)
			continue;

		switch (insn->off) {
		case JMP_TO_ERROR_CODE:
			target = error_code;
			break;
		case JMP_TO_SUCCESS_CODE:
			target = success_code;
			break;
		case JMP_TO_USER_CODE:
			target = user_code;
			break;
		default:
			pr_err("bpf prologue: internal error: relocation failed\n");
			return -BPF_LOADER_ERRNO__PROLOGUE;
		}

		insn->off = target - (insn + 1);
	}
	return 0;
}

int bpf__gen_prologue(struct probe_trace_arg *args, int nargs,
		      struct bpf_insn *new_prog, size_t *new_cnt,
		      size_t cnt_space)
{
	struct bpf_insn *success_code = NULL;
	struct bpf_insn *error_code = NULL;
	struct bpf_insn *user_code = NULL;
	struct bpf_insn_pos pos;
	bool fastpath = true;
	int err = 0, i;

	if (!new_prog || !new_cnt)
		return -EINVAL;

	if (cnt_space > BPF_MAXINSNS)
		cnt_space = BPF_MAXINSNS;

	pos.begin = new_prog;
	pos.end = new_prog + cnt_space;
	pos.pos = new_prog;

	if (!nargs) {
		ins(BPF_ALU64_IMM(BPF_MOV, BPF_PROLOGUE_FETCH_RESULT_REG, 0),
		    &pos);

		if (check_pos(&pos))
			goto errout;

		*new_cnt = pos_get_cnt(&pos);
		return 0;
	}

	if (nargs > BPF_PROLOGUE_MAX_ARGS) {
		pr_warning("bpf: prologue: %d arguments are dropped\n",
			   nargs - BPF_PROLOGUE_MAX_ARGS);
		nargs = BPF_PROLOGUE_MAX_ARGS;
	}

	/* First pass: validation */
	for (i = 0; i < nargs; i++) {
		struct probe_trace_arg_ref *ref = args[i].ref;

		if (args[i].value[0] == '@') {
			/* TODO: fetch global variable */
			pr_err("bpf: prologue: global %s%+ld not support\n",
				args[i].value, ref ? ref->offset : 0);
			return -ENOTSUP;
		}

		while (ref) {
			/* fastpath is true if all args has ref == NULL */
			fastpath = false;

			/*
			 * Instruction encodes immediate value using
			 * s32, ref->offset is long. On systems which
			 * can't fill long in s32, refuse to process if
			 * ref->offset too large (or small).
			 */
#ifdef __LP64__
#define OFFSET_MAX	((1LL << 31) - 1)
#define OFFSET_MIN	((1LL << 31) * -1)
			if (ref->offset > OFFSET_MAX ||
					ref->offset < OFFSET_MIN) {
				pr_err("bpf: prologue: offset out of bound: %ld\n",
				       ref->offset);
				return -BPF_LOADER_ERRNO__PROLOGUEOOB;
			}
#endif
			ref = ref->next;
		}
	}
	pr_debug("prologue: pass validation\n");

	if (fastpath) {
		/* If all variables are registers... */
		pr_debug("prologue: fast path\n");
		err = gen_prologue_fastpath(&pos, args, nargs);
		if (err)
			goto errout;
	} else {
		pr_debug("prologue: slow path\n");

		/* Initialization: move ctx to a callee saved register. */
		ins(BPF_MOV64_REG(BPF_REG_CTX, BPF_REG_ARG1), &pos);

		err = gen_prologue_slowpath(&pos, args, nargs);
		if (err)
			goto errout;
		/*
		 * start of ERROR_CODE (only slow pass needs error code)
		 *   mov r2 <- 1  // r2 is error number
		 *   mov r3 <- 0  // r3, r4... should be touched or
		 *                // verifier would complain
		 *   mov r4 <- 0
		 *   ...
		 *   goto usercode
		 */
		error_code = pos.pos;
		ins(BPF_ALU64_IMM(BPF_MOV, BPF_PROLOGUE_FETCH_RESULT_REG, 1),
		    &pos);

		for (i = 0; i < nargs; i++)
			ins(BPF_ALU64_IMM(BPF_MOV,
					  BPF_PROLOGUE_START_ARG_REG + i,
					  0),
			    &pos);
		ins(BPF_JMP_IMM(BPF_JA, BPF_REG_0, 0, JMP_TO_USER_CODE),
				&pos);
	}

	/*
	 * start of SUCCESS_CODE:
	 *   mov r2 <- 0
	 *   goto usercode  // skip
	 */
	success_code = pos.pos;
	ins(BPF_ALU64_IMM(BPF_MOV, BPF_PROLOGUE_FETCH_RESULT_REG, 0), &pos);

	/*
	 * start of USER_CODE:
	 *   Restore ctx to r1
	 */
	user_code = pos.pos;
	if (!fastpath) {
		/*
		 * Only slow path needs restoring of ctx. In fast path,
		 * register are loaded directly from r1.
		 */
		ins(BPF_MOV64_REG(BPF_REG_ARG1, BPF_REG_CTX), &pos);
		err = prologue_relocate(&pos, error_code, success_code,
					user_code);
		if (err)
			goto errout;
	}

	err = check_pos(&pos);
	if (err)
		goto errout;

	*new_cnt = pos_get_cnt(&pos);
	return 0;
errout:
	return err;
}