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1/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
2#ifndef __BPF_CORE_READ_H__
3#define __BPF_CORE_READ_H__
4
5/*
6 * enum bpf_field_info_kind is passed as a second argument into
7 * __builtin_preserve_field_info() built-in to get a specific aspect of
8 * a field, captured as a first argument. __builtin_preserve_field_info(field,
9 * info_kind) returns __u32 integer and produces BTF field relocation, which
10 * is understood and processed by libbpf during BPF object loading. See
11 * selftests/bpf for examples.
12 */
13enum bpf_field_info_kind {
14 BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
15 BPF_FIELD_BYTE_SIZE = 1,
16 BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
17 BPF_FIELD_SIGNED = 3,
18 BPF_FIELD_LSHIFT_U64 = 4,
19 BPF_FIELD_RSHIFT_U64 = 5,
20};
21
22/* second argument to __builtin_btf_type_id() built-in */
23enum bpf_type_id_kind {
24 BPF_TYPE_ID_LOCAL = 0, /* BTF type ID in local program */
25 BPF_TYPE_ID_TARGET = 1, /* BTF type ID in target kernel */
26};
27
28/* second argument to __builtin_preserve_type_info() built-in */
29enum bpf_type_info_kind {
30 BPF_TYPE_EXISTS = 0, /* type existence in target kernel */
31 BPF_TYPE_SIZE = 1, /* type size in target kernel */
32 BPF_TYPE_MATCHES = 2, /* type match in target kernel */
33};
34
35/* second argument to __builtin_preserve_enum_value() built-in */
36enum bpf_enum_value_kind {
37 BPF_ENUMVAL_EXISTS = 0, /* enum value existence in kernel */
38 BPF_ENUMVAL_VALUE = 1, /* enum value value relocation */
39};
40
41#define __CORE_RELO(src, field, info) \
42 __builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
43
44#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
45#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
46 bpf_probe_read_kernel( \
47 (void *)dst, \
48 __CORE_RELO(src, fld, BYTE_SIZE), \
49 (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
50#else
51/* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
52 * for big-endian we need to adjust destination pointer accordingly, based on
53 * field byte size
54 */
55#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
56 bpf_probe_read_kernel( \
57 (void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)), \
58 __CORE_RELO(src, fld, BYTE_SIZE), \
59 (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
60#endif
61
62/*
63 * Extract bitfield, identified by s->field, and return its value as u64.
64 * All this is done in relocatable manner, so bitfield changes such as
65 * signedness, bit size, offset changes, this will be handled automatically.
66 * This version of macro is using bpf_probe_read_kernel() to read underlying
67 * integer storage. Macro functions as an expression and its return type is
68 * bpf_probe_read_kernel()'s return value: 0, on success, <0 on error.
69 */
70#define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({ \
71 unsigned long long val = 0; \
72 \
73 __CORE_BITFIELD_PROBE_READ(&val, s, field); \
74 val <<= __CORE_RELO(s, field, LSHIFT_U64); \
75 if (__CORE_RELO(s, field, SIGNED)) \
76 val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \
77 else \
78 val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
79 val; \
80})
81
82/*
83 * Extract bitfield, identified by s->field, and return its value as u64.
84 * This version of macro is using direct memory reads and should be used from
85 * BPF program types that support such functionality (e.g., typed raw
86 * tracepoints).
87 */
88#define BPF_CORE_READ_BITFIELD(s, field) ({ \
89 const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
90 unsigned long long val; \
91 \
92 /* This is a so-called barrier_var() operation that makes specified \
93 * variable "a black box" for optimizing compiler. \
94 * It forces compiler to perform BYTE_OFFSET relocation on p and use \
95 * its calculated value in the switch below, instead of applying \
96 * the same relocation 4 times for each individual memory load. \
97 */ \
98 asm volatile("" : "=r"(p) : "0"(p)); \
99 \
100 switch (__CORE_RELO(s, field, BYTE_SIZE)) { \
101 case 1: val = *(const unsigned char *)p; break; \
102 case 2: val = *(const unsigned short *)p; break; \
103 case 4: val = *(const unsigned int *)p; break; \
104 case 8: val = *(const unsigned long long *)p; break; \
105 } \
106 val <<= __CORE_RELO(s, field, LSHIFT_U64); \
107 if (__CORE_RELO(s, field, SIGNED)) \
108 val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \
109 else \
110 val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
111 val; \
112})
113
114#define ___bpf_field_ref1(field) (field)
115#define ___bpf_field_ref2(type, field) (((typeof(type) *)0)->field)
116#define ___bpf_field_ref(args...) \
117 ___bpf_apply(___bpf_field_ref, ___bpf_narg(args))(args)
118
119/*
120 * Convenience macro to check that field actually exists in target kernel's.
121 * Returns:
122 * 1, if matching field is present in target kernel;
123 * 0, if no matching field found.
124 *
125 * Supports two forms:
126 * - field reference through variable access:
127 * bpf_core_field_exists(p->my_field);
128 * - field reference through type and field names:
129 * bpf_core_field_exists(struct my_type, my_field).
130 */
131#define bpf_core_field_exists(field...) \
132 __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_EXISTS)
133
134/*
135 * Convenience macro to get the byte size of a field. Works for integers,
136 * struct/unions, pointers, arrays, and enums.
137 *
138 * Supports two forms:
139 * - field reference through variable access:
140 * bpf_core_field_size(p->my_field);
141 * - field reference through type and field names:
142 * bpf_core_field_size(struct my_type, my_field).
143 */
144#define bpf_core_field_size(field...) \
145 __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_SIZE)
146
147/*
148 * Convenience macro to get field's byte offset.
149 *
150 * Supports two forms:
151 * - field reference through variable access:
152 * bpf_core_field_offset(p->my_field);
153 * - field reference through type and field names:
154 * bpf_core_field_offset(struct my_type, my_field).
155 */
156#define bpf_core_field_offset(field...) \
157 __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_OFFSET)
158
159/*
160 * Convenience macro to get BTF type ID of a specified type, using a local BTF
161 * information. Return 32-bit unsigned integer with type ID from program's own
162 * BTF. Always succeeds.
163 */
164#define bpf_core_type_id_local(type) \
165 __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_LOCAL)
166
167/*
168 * Convenience macro to get BTF type ID of a target kernel's type that matches
169 * specified local type.
170 * Returns:
171 * - valid 32-bit unsigned type ID in kernel BTF;
172 * - 0, if no matching type was found in a target kernel BTF.
173 */
174#define bpf_core_type_id_kernel(type) \
175 __builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_TARGET)
176
177/*
178 * Convenience macro to check that provided named type
179 * (struct/union/enum/typedef) exists in a target kernel.
180 * Returns:
181 * 1, if such type is present in target kernel's BTF;
182 * 0, if no matching type is found.
183 */
184#define bpf_core_type_exists(type) \
185 __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_EXISTS)
186
187/*
188 * Convenience macro to check that provided named type
189 * (struct/union/enum/typedef) "matches" that in a target kernel.
190 * Returns:
191 * 1, if the type matches in the target kernel's BTF;
192 * 0, if the type does not match any in the target kernel
193 */
194#define bpf_core_type_matches(type) \
195 __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_MATCHES)
196
197/*
198 * Convenience macro to get the byte size of a provided named type
199 * (struct/union/enum/typedef) in a target kernel.
200 * Returns:
201 * >= 0 size (in bytes), if type is present in target kernel's BTF;
202 * 0, if no matching type is found.
203 */
204#define bpf_core_type_size(type) \
205 __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_SIZE)
206
207/*
208 * Convenience macro to check that provided enumerator value is defined in
209 * a target kernel.
210 * Returns:
211 * 1, if specified enum type and its enumerator value are present in target
212 * kernel's BTF;
213 * 0, if no matching enum and/or enum value within that enum is found.
214 */
215#define bpf_core_enum_value_exists(enum_type, enum_value) \
216 __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_EXISTS)
217
218/*
219 * Convenience macro to get the integer value of an enumerator value in
220 * a target kernel.
221 * Returns:
222 * 64-bit value, if specified enum type and its enumerator value are
223 * present in target kernel's BTF;
224 * 0, if no matching enum and/or enum value within that enum is found.
225 */
226#define bpf_core_enum_value(enum_type, enum_value) \
227 __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE)
228
229/*
230 * bpf_core_read() abstracts away bpf_probe_read_kernel() call and captures
231 * offset relocation for source address using __builtin_preserve_access_index()
232 * built-in, provided by Clang.
233 *
234 * __builtin_preserve_access_index() takes as an argument an expression of
235 * taking an address of a field within struct/union. It makes compiler emit
236 * a relocation, which records BTF type ID describing root struct/union and an
237 * accessor string which describes exact embedded field that was used to take
238 * an address. See detailed description of this relocation format and
239 * semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
240 *
241 * This relocation allows libbpf to adjust BPF instruction to use correct
242 * actual field offset, based on target kernel BTF type that matches original
243 * (local) BTF, used to record relocation.
244 */
245#define bpf_core_read(dst, sz, src) \
246 bpf_probe_read_kernel(dst, sz, (const void *)__builtin_preserve_access_index(src))
247
248/* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use. */
249#define bpf_core_read_user(dst, sz, src) \
250 bpf_probe_read_user(dst, sz, (const void *)__builtin_preserve_access_index(src))
251/*
252 * bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
253 * additionally emitting BPF CO-RE field relocation for specified source
254 * argument.
255 */
256#define bpf_core_read_str(dst, sz, src) \
257 bpf_probe_read_kernel_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
258
259/* NOTE: see comments for BPF_CORE_READ_USER() about the proper types use. */
260#define bpf_core_read_user_str(dst, sz, src) \
261 bpf_probe_read_user_str(dst, sz, (const void *)__builtin_preserve_access_index(src))
262
263#define ___concat(a, b) a ## b
264#define ___apply(fn, n) ___concat(fn, n)
265#define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N
266
267/*
268 * return number of provided arguments; used for switch-based variadic macro
269 * definitions (see ___last, ___arrow, etc below)
270 */
271#define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
272/*
273 * return 0 if no arguments are passed, N - otherwise; used for
274 * recursively-defined macros to specify termination (0) case, and generic
275 * (N) case (e.g., ___read_ptrs, ___core_read)
276 */
277#define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
278
279#define ___last1(x) x
280#define ___last2(a, x) x
281#define ___last3(a, b, x) x
282#define ___last4(a, b, c, x) x
283#define ___last5(a, b, c, d, x) x
284#define ___last6(a, b, c, d, e, x) x
285#define ___last7(a, b, c, d, e, f, x) x
286#define ___last8(a, b, c, d, e, f, g, x) x
287#define ___last9(a, b, c, d, e, f, g, h, x) x
288#define ___last10(a, b, c, d, e, f, g, h, i, x) x
289#define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__)
290
291#define ___nolast2(a, _) a
292#define ___nolast3(a, b, _) a, b
293#define ___nolast4(a, b, c, _) a, b, c
294#define ___nolast5(a, b, c, d, _) a, b, c, d
295#define ___nolast6(a, b, c, d, e, _) a, b, c, d, e
296#define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f
297#define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g
298#define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h
299#define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i
300#define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__)
301
302#define ___arrow1(a) a
303#define ___arrow2(a, b) a->b
304#define ___arrow3(a, b, c) a->b->c
305#define ___arrow4(a, b, c, d) a->b->c->d
306#define ___arrow5(a, b, c, d, e) a->b->c->d->e
307#define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f
308#define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g
309#define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h
310#define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i
311#define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
312#define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)
313
314#define ___type(...) typeof(___arrow(__VA_ARGS__))
315
316#define ___read(read_fn, dst, src_type, src, accessor) \
317 read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
318
319/* "recursively" read a sequence of inner pointers using local __t var */
320#define ___rd_first(fn, src, a) ___read(fn, &__t, ___type(src), src, a);
321#define ___rd_last(fn, ...) \
322 ___read(fn, &__t, ___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
323#define ___rd_p1(fn, ...) const void *__t; ___rd_first(fn, __VA_ARGS__)
324#define ___rd_p2(fn, ...) ___rd_p1(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
325#define ___rd_p3(fn, ...) ___rd_p2(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
326#define ___rd_p4(fn, ...) ___rd_p3(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
327#define ___rd_p5(fn, ...) ___rd_p4(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
328#define ___rd_p6(fn, ...) ___rd_p5(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
329#define ___rd_p7(fn, ...) ___rd_p6(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
330#define ___rd_p8(fn, ...) ___rd_p7(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
331#define ___rd_p9(fn, ...) ___rd_p8(fn, ___nolast(__VA_ARGS__)) ___rd_last(fn, __VA_ARGS__)
332#define ___read_ptrs(fn, src, ...) \
333 ___apply(___rd_p, ___narg(__VA_ARGS__))(fn, src, __VA_ARGS__)
334
335#define ___core_read0(fn, fn_ptr, dst, src, a) \
336 ___read(fn, dst, ___type(src), src, a);
337#define ___core_readN(fn, fn_ptr, dst, src, ...) \
338 ___read_ptrs(fn_ptr, src, ___nolast(__VA_ARGS__)) \
339 ___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t, \
340 ___last(__VA_ARGS__));
341#define ___core_read(fn, fn_ptr, dst, src, a, ...) \
342 ___apply(___core_read, ___empty(__VA_ARGS__))(fn, fn_ptr, dst, \
343 src, a, ##__VA_ARGS__)
344
345/*
346 * BPF_CORE_READ_INTO() is a more performance-conscious variant of
347 * BPF_CORE_READ(), in which final field is read into user-provided storage.
348 * See BPF_CORE_READ() below for more details on general usage.
349 */
350#define BPF_CORE_READ_INTO(dst, src, a, ...) ({ \
351 ___core_read(bpf_core_read, bpf_core_read, \
352 dst, (src), a, ##__VA_ARGS__) \
353})
354
355/*
356 * Variant of BPF_CORE_READ_INTO() for reading from user-space memory.
357 *
358 * NOTE: see comments for BPF_CORE_READ_USER() about the proper types use.
359 */
360#define BPF_CORE_READ_USER_INTO(dst, src, a, ...) ({ \
361 ___core_read(bpf_core_read_user, bpf_core_read_user, \
362 dst, (src), a, ##__VA_ARGS__) \
363})
364
365/* Non-CO-RE variant of BPF_CORE_READ_INTO() */
366#define BPF_PROBE_READ_INTO(dst, src, a, ...) ({ \
367 ___core_read(bpf_probe_read, bpf_probe_read, \
368 dst, (src), a, ##__VA_ARGS__) \
369})
370
371/* Non-CO-RE variant of BPF_CORE_READ_USER_INTO().
372 *
373 * As no CO-RE relocations are emitted, source types can be arbitrary and are
374 * not restricted to kernel types only.
375 */
376#define BPF_PROBE_READ_USER_INTO(dst, src, a, ...) ({ \
377 ___core_read(bpf_probe_read_user, bpf_probe_read_user, \
378 dst, (src), a, ##__VA_ARGS__) \
379})
380
381/*
382 * BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
383 * BPF_CORE_READ() for intermediate pointers, but then executes (and returns
384 * corresponding error code) bpf_core_read_str() for final string read.
385 */
386#define BPF_CORE_READ_STR_INTO(dst, src, a, ...) ({ \
387 ___core_read(bpf_core_read_str, bpf_core_read, \
388 dst, (src), a, ##__VA_ARGS__) \
389})
390
391/*
392 * Variant of BPF_CORE_READ_STR_INTO() for reading from user-space memory.
393 *
394 * NOTE: see comments for BPF_CORE_READ_USER() about the proper types use.
395 */
396#define BPF_CORE_READ_USER_STR_INTO(dst, src, a, ...) ({ \
397 ___core_read(bpf_core_read_user_str, bpf_core_read_user, \
398 dst, (src), a, ##__VA_ARGS__) \
399})
400
401/* Non-CO-RE variant of BPF_CORE_READ_STR_INTO() */
402#define BPF_PROBE_READ_STR_INTO(dst, src, a, ...) ({ \
403 ___core_read(bpf_probe_read_str, bpf_probe_read, \
404 dst, (src), a, ##__VA_ARGS__) \
405})
406
407/*
408 * Non-CO-RE variant of BPF_CORE_READ_USER_STR_INTO().
409 *
410 * As no CO-RE relocations are emitted, source types can be arbitrary and are
411 * not restricted to kernel types only.
412 */
413#define BPF_PROBE_READ_USER_STR_INTO(dst, src, a, ...) ({ \
414 ___core_read(bpf_probe_read_user_str, bpf_probe_read_user, \
415 dst, (src), a, ##__VA_ARGS__) \
416})
417
418/*
419 * BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
420 * when there are few pointer chasing steps.
421 * E.g., what in non-BPF world (or in BPF w/ BCC) would be something like:
422 * int x = s->a.b.c->d.e->f->g;
423 * can be succinctly achieved using BPF_CORE_READ as:
424 * int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
425 *
426 * BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
427 * CO-RE relocatable bpf_probe_read_kernel() wrapper) calls, logically
428 * equivalent to:
429 * 1. const void *__t = s->a.b.c;
430 * 2. __t = __t->d.e;
431 * 3. __t = __t->f;
432 * 4. return __t->g;
433 *
434 * Equivalence is logical, because there is a heavy type casting/preservation
435 * involved, as well as all the reads are happening through
436 * bpf_probe_read_kernel() calls using __builtin_preserve_access_index() to
437 * emit CO-RE relocations.
438 *
439 * N.B. Only up to 9 "field accessors" are supported, which should be more
440 * than enough for any practical purpose.
441 */
442#define BPF_CORE_READ(src, a, ...) ({ \
443 ___type((src), a, ##__VA_ARGS__) __r; \
444 BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \
445 __r; \
446})
447
448/*
449 * Variant of BPF_CORE_READ() for reading from user-space memory.
450 *
451 * NOTE: all the source types involved are still *kernel types* and need to
452 * exist in kernel (or kernel module) BTF, otherwise CO-RE relocation will
453 * fail. Custom user types are not relocatable with CO-RE.
454 * The typical situation in which BPF_CORE_READ_USER() might be used is to
455 * read kernel UAPI types from the user-space memory passed in as a syscall
456 * input argument.
457 */
458#define BPF_CORE_READ_USER(src, a, ...) ({ \
459 ___type((src), a, ##__VA_ARGS__) __r; \
460 BPF_CORE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
461 __r; \
462})
463
464/* Non-CO-RE variant of BPF_CORE_READ() */
465#define BPF_PROBE_READ(src, a, ...) ({ \
466 ___type((src), a, ##__VA_ARGS__) __r; \
467 BPF_PROBE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \
468 __r; \
469})
470
471/*
472 * Non-CO-RE variant of BPF_CORE_READ_USER().
473 *
474 * As no CO-RE relocations are emitted, source types can be arbitrary and are
475 * not restricted to kernel types only.
476 */
477#define BPF_PROBE_READ_USER(src, a, ...) ({ \
478 ___type((src), a, ##__VA_ARGS__) __r; \
479 BPF_PROBE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
480 __r; \
481})
482
483#endif
484