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