// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) /* Copyright (c) 2019 Facebook */ #ifdef __KERNEL__ #include #include #include #include #include "relo_core.h" static const char *btf_kind_str(const struct btf_type *t) { return btf_type_str(t); } static bool is_ldimm64_insn(struct bpf_insn *insn) { return insn->code == (BPF_LD | BPF_IMM | BPF_DW); } static const struct btf_type * skip_mods_and_typedefs(const struct btf *btf, u32 id, u32 *res_id) { return btf_type_skip_modifiers(btf, id, res_id); } static const char *btf__name_by_offset(const struct btf *btf, u32 offset) { return btf_name_by_offset(btf, offset); } static s64 btf__resolve_size(const struct btf *btf, u32 type_id) { const struct btf_type *t; int size; t = btf_type_by_id(btf, type_id); t = btf_resolve_size(btf, t, &size); if (IS_ERR(t)) return PTR_ERR(t); return size; } enum libbpf_print_level { LIBBPF_WARN, LIBBPF_INFO, LIBBPF_DEBUG, }; #undef pr_warn #undef pr_info #undef pr_debug #define pr_warn(fmt, log, ...) bpf_log((void *)log, fmt, "", ##__VA_ARGS__) #define pr_info(fmt, log, ...) bpf_log((void *)log, fmt, "", ##__VA_ARGS__) #define pr_debug(fmt, log, ...) bpf_log((void *)log, fmt, "", ##__VA_ARGS__) #define libbpf_print(level, fmt, ...) bpf_log((void *)prog_name, fmt, ##__VA_ARGS__) #else #include #include #include #include #include #include "libbpf.h" #include "bpf.h" #include "btf.h" #include "str_error.h" #include "libbpf_internal.h" #endif static bool is_flex_arr(const struct btf *btf, const struct bpf_core_accessor *acc, const struct btf_array *arr) { const struct btf_type *t; /* not a flexible array, if not inside a struct or has non-zero size */ if (!acc->name || arr->nelems > 0) return false; /* has to be the last member of enclosing struct */ t = btf_type_by_id(btf, acc->type_id); return acc->idx == btf_vlen(t) - 1; } static const char *core_relo_kind_str(enum bpf_core_relo_kind kind) { switch (kind) { case BPF_CORE_FIELD_BYTE_OFFSET: return "byte_off"; case BPF_CORE_FIELD_BYTE_SIZE: return "byte_sz"; case BPF_CORE_FIELD_EXISTS: return "field_exists"; case BPF_CORE_FIELD_SIGNED: return "signed"; case BPF_CORE_FIELD_LSHIFT_U64: return "lshift_u64"; case BPF_CORE_FIELD_RSHIFT_U64: return "rshift_u64"; case BPF_CORE_TYPE_ID_LOCAL: return "local_type_id"; case BPF_CORE_TYPE_ID_TARGET: return "target_type_id"; case BPF_CORE_TYPE_EXISTS: return "type_exists"; case BPF_CORE_TYPE_SIZE: return "type_size"; case BPF_CORE_ENUMVAL_EXISTS: return "enumval_exists"; case BPF_CORE_ENUMVAL_VALUE: return "enumval_value"; default: return "unknown"; } } static bool core_relo_is_field_based(enum bpf_core_relo_kind kind) { switch (kind) { case BPF_CORE_FIELD_BYTE_OFFSET: case BPF_CORE_FIELD_BYTE_SIZE: case BPF_CORE_FIELD_EXISTS: case BPF_CORE_FIELD_SIGNED: case BPF_CORE_FIELD_LSHIFT_U64: case BPF_CORE_FIELD_RSHIFT_U64: return true; default: return false; } } static bool core_relo_is_type_based(enum bpf_core_relo_kind kind) { switch (kind) { case BPF_CORE_TYPE_ID_LOCAL: case BPF_CORE_TYPE_ID_TARGET: case BPF_CORE_TYPE_EXISTS: case BPF_CORE_TYPE_SIZE: return true; default: return false; } } static bool core_relo_is_enumval_based(enum bpf_core_relo_kind kind) { switch (kind) { case BPF_CORE_ENUMVAL_EXISTS: case BPF_CORE_ENUMVAL_VALUE: return true; default: return false; } } /* * Turn bpf_core_relo into a low- and high-level spec representation, * validating correctness along the way, as well as calculating resulting * field bit offset, specified by accessor string. Low-level spec captures * every single level of nestedness, including traversing anonymous * struct/union members. High-level one only captures semantically meaningful * "turning points": named fields and array indicies. * E.g., for this case: * * struct sample { * int __unimportant; * struct { * int __1; * int __2; * int a[7]; * }; * }; * * struct sample *s = ...; * * int x = &s->a[3]; // access string = '0:1:2:3' * * Low-level spec has 1:1 mapping with each element of access string (it's * just a parsed access string representation): [0, 1, 2, 3]. * * High-level spec will capture only 3 points: * - intial zero-index access by pointer (&s->... is the same as &s[0]...); * - field 'a' access (corresponds to '2' in low-level spec); * - array element #3 access (corresponds to '3' in low-level spec). * * Type-based relocations (TYPE_EXISTS/TYPE_SIZE, * TYPE_ID_LOCAL/TYPE_ID_TARGET) don't capture any field information. Their * spec and raw_spec are kept empty. * * Enum value-based relocations (ENUMVAL_EXISTS/ENUMVAL_VALUE) use access * string to specify enumerator's value index that need to be relocated. */ static int bpf_core_parse_spec(const char *prog_name, const struct btf *btf, __u32 type_id, const char *spec_str, enum bpf_core_relo_kind relo_kind, struct bpf_core_spec *spec) { int access_idx, parsed_len, i; struct bpf_core_accessor *acc; const struct btf_type *t; const char *name; __u32 id; __s64 sz; if (str_is_empty(spec_str) || *spec_str == ':') return -EINVAL; memset(spec, 0, sizeof(*spec)); spec->btf = btf; spec->root_type_id = type_id; spec->relo_kind = relo_kind; /* type-based relocations don't have a field access string */ if (core_relo_is_type_based(relo_kind)) { if (strcmp(spec_str, "0")) return -EINVAL; return 0; } /* parse spec_str="0:1:2:3:4" into array raw_spec=[0, 1, 2, 3, 4] */ while (*spec_str) { if (*spec_str == ':') ++spec_str; if (sscanf(spec_str, "%d%n", &access_idx, &parsed_len) != 1) return -EINVAL; if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN) return -E2BIG; spec_str += parsed_len; spec->raw_spec[spec->raw_len++] = access_idx; } if (spec->raw_len == 0) return -EINVAL; t = skip_mods_and_typedefs(btf, type_id, &id); if (!t) return -EINVAL; access_idx = spec->raw_spec[0]; acc = &spec->spec[0]; acc->type_id = id; acc->idx = access_idx; spec->len++; if (core_relo_is_enumval_based(relo_kind)) { if (!btf_is_enum(t) || spec->raw_len > 1 || access_idx >= btf_vlen(t)) return -EINVAL; /* record enumerator name in a first accessor */ acc->name = btf__name_by_offset(btf, btf_enum(t)[access_idx].name_off); return 0; } if (!core_relo_is_field_based(relo_kind)) return -EINVAL; sz = btf__resolve_size(btf, id); if (sz < 0) return sz; spec->bit_offset = access_idx * sz * 8; for (i = 1; i < spec->raw_len; i++) { t = skip_mods_and_typedefs(btf, id, &id); if (!t) return -EINVAL; access_idx = spec->raw_spec[i]; acc = &spec->spec[spec->len]; if (btf_is_composite(t)) { const struct btf_member *m; __u32 bit_offset; if (access_idx >= btf_vlen(t)) return -EINVAL; bit_offset = btf_member_bit_offset(t, access_idx); spec->bit_offset += bit_offset; m = btf_members(t) + access_idx; if (m->name_off) { name = btf__name_by_offset(btf, m->name_off); if (str_is_empty(name)) return -EINVAL; acc->type_id = id; acc->idx = access_idx; acc->name = name; spec->len++; } id = m->type; } else if (btf_is_array(t)) { const struct btf_array *a = btf_array(t); bool flex; t = skip_mods_and_typedefs(btf, a->type, &id); if (!t) return -EINVAL; flex = is_flex_arr(btf, acc - 1, a); if (!flex && access_idx >= a->nelems) return -EINVAL; spec->spec[spec->len].type_id = id; spec->spec[spec->len].idx = access_idx; spec->len++; sz = btf__resolve_size(btf, id); if (sz < 0) return sz; spec->bit_offset += access_idx * sz * 8; } else { pr_warn("prog '%s': relo for [%u] %s (at idx %d) captures type [%d] of unexpected kind %s\n", prog_name, type_id, spec_str, i, id, btf_kind_str(t)); return -EINVAL; } } return 0; } /* Check two types for compatibility for the purpose of field access * relocation. const/volatile/restrict and typedefs are skipped to ensure we * are relocating semantically compatible entities: * - any two STRUCTs/UNIONs are compatible and can be mixed; * - any two FWDs are compatible, if their names match (modulo flavor suffix); * - any two PTRs are always compatible; * - for ENUMs, names should be the same (ignoring flavor suffix) or at * least one of enums should be anonymous; * - for ENUMs, check sizes, names are ignored; * - for INT, size and signedness are ignored; * - any two FLOATs are always compatible; * - for ARRAY, dimensionality is ignored, element types are checked for * compatibility recursively; * - everything else shouldn't be ever a target of relocation. * These rules are not set in stone and probably will be adjusted as we get * more experience with using BPF CO-RE relocations. */ static int bpf_core_fields_are_compat(const struct btf *local_btf, __u32 local_id, const struct btf *targ_btf, __u32 targ_id) { const struct btf_type *local_type, *targ_type; recur: local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id); targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id); if (!local_type || !targ_type) return -EINVAL; if (btf_is_composite(local_type) && btf_is_composite(targ_type)) return 1; if (btf_kind(local_type) != btf_kind(targ_type)) return 0; switch (btf_kind(local_type)) { case BTF_KIND_PTR: case BTF_KIND_FLOAT: return 1; case BTF_KIND_FWD: case BTF_KIND_ENUM: { const char *local_name, *targ_name; size_t local_len, targ_len; local_name = btf__name_by_offset(local_btf, local_type->name_off); targ_name = btf__name_by_offset(targ_btf, targ_type->name_off); local_len = bpf_core_essential_name_len(local_name); targ_len = bpf_core_essential_name_len(targ_name); /* one of them is anonymous or both w/ same flavor-less names */ return local_len == 0 || targ_len == 0 || (local_len == targ_len && strncmp(local_name, targ_name, local_len) == 0); } case BTF_KIND_INT: /* just reject deprecated bitfield-like integers; all other * integers are by default compatible between each other */ return btf_int_offset(local_type) == 0 && btf_int_offset(targ_type) == 0; case BTF_KIND_ARRAY: local_id = btf_array(local_type)->type; targ_id = btf_array(targ_type)->type; goto recur; default: return 0; } } /* * Given single high-level named field accessor in local type, find * corresponding high-level accessor for a target type. Along the way, * maintain low-level spec for target as well. Also keep updating target * bit offset. * * Searching is performed through recursive exhaustive enumeration of all * fields of a struct/union. If there are any anonymous (embedded) * structs/unions, they are recursively searched as well. If field with * desired name is found, check compatibility between local and target types, * before returning result. * * 1 is returned, if field is found. * 0 is returned if no compatible field is found. * <0 is returned on error. */ static int bpf_core_match_member(const struct btf *local_btf, const struct bpf_core_accessor *local_acc, const struct btf *targ_btf, __u32 targ_id, struct bpf_core_spec *spec, __u32 *next_targ_id) { const struct btf_type *local_type, *targ_type; const struct btf_member *local_member, *m; const char *local_name, *targ_name; __u32 local_id; int i, n, found; targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id); if (!targ_type) return -EINVAL; if (!btf_is_composite(targ_type)) return 0; local_id = local_acc->type_id; local_type = btf_type_by_id(local_btf, local_id); local_member = btf_members(local_type) + local_acc->idx; local_name = btf__name_by_offset(local_btf, local_member->name_off); n = btf_vlen(targ_type); m = btf_members(targ_type); for (i = 0; i < n; i++, m++) { __u32 bit_offset; bit_offset = btf_member_bit_offset(targ_type, i); /* too deep struct/union/array nesting */ if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN) return -E2BIG; /* speculate this member will be the good one */ spec->bit_offset += bit_offset; spec->raw_spec[spec->raw_len++] = i; targ_name = btf__name_by_offset(targ_btf, m->name_off); if (str_is_empty(targ_name)) { /* embedded struct/union, we need to go deeper */ found = bpf_core_match_member(local_btf, local_acc, targ_btf, m->type, spec, next_targ_id); if (found) /* either found or error */ return found; } else if (strcmp(local_name, targ_name) == 0) { /* matching named field */ struct bpf_core_accessor *targ_acc; targ_acc = &spec->spec[spec->len++]; targ_acc->type_id = targ_id; targ_acc->idx = i; targ_acc->name = targ_name; *next_targ_id = m->type; found = bpf_core_fields_are_compat(local_btf, local_member->type, targ_btf, m->type); if (!found) spec->len--; /* pop accessor */ return found; } /* member turned out not to be what we looked for */ spec->bit_offset -= bit_offset; spec->raw_len--; } return 0; } /* * Try to match local spec to a target type and, if successful, produce full * target spec (high-level, low-level + bit offset). */ static int bpf_core_spec_match(struct bpf_core_spec *local_spec, const struct btf *targ_btf, __u32 targ_id, struct bpf_core_spec *targ_spec) { const struct btf_type *targ_type; const struct bpf_core_accessor *local_acc; struct bpf_core_accessor *targ_acc; int i, sz, matched; memset(targ_spec, 0, sizeof(*targ_spec)); targ_spec->btf = targ_btf; targ_spec->root_type_id = targ_id; targ_spec->relo_kind = local_spec->relo_kind; if (core_relo_is_type_based(local_spec->relo_kind)) { return bpf_core_types_are_compat(local_spec->btf, local_spec->root_type_id, targ_btf, targ_id); } local_acc = &local_spec->spec[0]; targ_acc = &targ_spec->spec[0]; if (core_relo_is_enumval_based(local_spec->relo_kind)) { size_t local_essent_len, targ_essent_len; const struct btf_enum *e; const char *targ_name; /* has to resolve to an enum */ targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id, &targ_id); if (!btf_is_enum(targ_type)) return 0; local_essent_len = bpf_core_essential_name_len(local_acc->name); for (i = 0, e = btf_enum(targ_type); i < btf_vlen(targ_type); i++, e++) { targ_name = btf__name_by_offset(targ_spec->btf, e->name_off); targ_essent_len = bpf_core_essential_name_len(targ_name); if (targ_essent_len != local_essent_len) continue; if (strncmp(local_acc->name, targ_name, local_essent_len) == 0) { targ_acc->type_id = targ_id; targ_acc->idx = i; targ_acc->name = targ_name; targ_spec->len++; targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx; targ_spec->raw_len++; return 1; } } return 0; } if (!core_relo_is_field_based(local_spec->relo_kind)) return -EINVAL; for (i = 0; i < local_spec->len; i++, local_acc++, targ_acc++) { targ_type = skip_mods_and_typedefs(targ_spec->btf, targ_id, &targ_id); if (!targ_type) return -EINVAL; if (local_acc->name) { matched = bpf_core_match_member(local_spec->btf, local_acc, targ_btf, targ_id, targ_spec, &targ_id); if (matched <= 0) return matched; } else { /* for i=0, targ_id is already treated as array element * type (because it's the original struct), for others * we should find array element type first */ if (i > 0) { const struct btf_array *a; bool flex; if (!btf_is_array(targ_type)) return 0; a = btf_array(targ_type); flex = is_flex_arr(targ_btf, targ_acc - 1, a); if (!flex && local_acc->idx >= a->nelems) return 0; if (!skip_mods_and_typedefs(targ_btf, a->type, &targ_id)) return -EINVAL; } /* too deep struct/union/array nesting */ if (targ_spec->raw_len == BPF_CORE_SPEC_MAX_LEN) return -E2BIG; targ_acc->type_id = targ_id; targ_acc->idx = local_acc->idx; targ_acc->name = NULL; targ_spec->len++; targ_spec->raw_spec[targ_spec->raw_len] = targ_acc->idx; targ_spec->raw_len++; sz = btf__resolve_size(targ_btf, targ_id); if (sz < 0) return sz; targ_spec->bit_offset += local_acc->idx * sz * 8; } } return 1; } static int bpf_core_calc_field_relo(const char *prog_name, const struct bpf_core_relo *relo, const struct bpf_core_spec *spec, __u32 *val, __u32 *field_sz, __u32 *type_id, bool *validate) { const struct bpf_core_accessor *acc; const struct btf_type *t; __u32 byte_off, byte_sz, bit_off, bit_sz, field_type_id; const struct btf_member *m; const struct btf_type *mt; bool bitfield; __s64 sz; *field_sz = 0; if (relo->kind == BPF_CORE_FIELD_EXISTS) { *val = spec ? 1 : 0; return 0; } if (!spec) return -EUCLEAN; /* request instruction poisoning */ acc = &spec->spec[spec->len - 1]; t = btf_type_by_id(spec->btf, acc->type_id); /* a[n] accessor needs special handling */ if (!acc->name) { if (relo->kind == BPF_CORE_FIELD_BYTE_OFFSET) { *val = spec->bit_offset / 8; /* remember field size for load/store mem size */ sz = btf__resolve_size(spec->btf, acc->type_id); if (sz < 0) return -EINVAL; *field_sz = sz; *type_id = acc->type_id; } else if (relo->kind == BPF_CORE_FIELD_BYTE_SIZE) { sz = btf__resolve_size(spec->btf, acc->type_id); if (sz < 0) return -EINVAL; *val = sz; } else { pr_warn("prog '%s': relo %d at insn #%d can't be applied to array access\n", prog_name, relo->kind, relo->insn_off / 8); return -EINVAL; } if (validate) *validate = true; return 0; } m = btf_members(t) + acc->idx; mt = skip_mods_and_typedefs(spec->btf, m->type, &field_type_id); bit_off = spec->bit_offset; bit_sz = btf_member_bitfield_size(t, acc->idx); bitfield = bit_sz > 0; if (bitfield) { byte_sz = mt->size; byte_off = bit_off / 8 / byte_sz * byte_sz; /* figure out smallest int size necessary for bitfield load */ while (bit_off + bit_sz - byte_off * 8 > byte_sz * 8) { if (byte_sz >= 8) { /* bitfield can't be read with 64-bit read */ pr_warn("prog '%s': relo %d at insn #%d can't be satisfied for bitfield\n", prog_name, relo->kind, relo->insn_off / 8); return -E2BIG; } byte_sz *= 2; byte_off = bit_off / 8 / byte_sz * byte_sz; } } else { sz = btf__resolve_size(spec->btf, field_type_id); if (sz < 0) return -EINVAL; byte_sz = sz; byte_off = spec->bit_offset / 8; bit_sz = byte_sz * 8; } /* for bitfields, all the relocatable aspects are ambiguous and we * might disagree with compiler, so turn off validation of expected * value, except for signedness */ if (validate) *validate = !bitfield; switch (relo->kind) { case BPF_CORE_FIELD_BYTE_OFFSET: *val = byte_off; if (!bitfield) { *field_sz = byte_sz; *type_id = field_type_id; } break; case BPF_CORE_FIELD_BYTE_SIZE: *val = byte_sz; break; case BPF_CORE_FIELD_SIGNED: /* enums will be assumed unsigned */ *val = btf_is_enum(mt) || (btf_int_encoding(mt) & BTF_INT_SIGNED); if (validate) *validate = true; /* signedness is never ambiguous */ break; case BPF_CORE_FIELD_LSHIFT_U64: #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ *val = 64 - (bit_off + bit_sz - byte_off * 8); #else *val = (8 - byte_sz) * 8 + (bit_off - byte_off * 8); #endif break; case BPF_CORE_FIELD_RSHIFT_U64: *val = 64 - bit_sz; if (validate) *validate = true; /* right shift is never ambiguous */ break; case BPF_CORE_FIELD_EXISTS: default: return -EOPNOTSUPP; } return 0; } static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo, const struct bpf_core_spec *spec, __u32 *val, bool *validate) { __s64 sz; /* by default, always check expected value in bpf_insn */ if (validate) *validate = true; /* type-based relos return zero when target type is not found */ if (!spec) { *val = 0; return 0; } switch (relo->kind) { case BPF_CORE_TYPE_ID_TARGET: *val = spec->root_type_id; /* type ID, embedded in bpf_insn, might change during linking, * so enforcing it is pointless */ if (validate) *validate = false; break; case BPF_CORE_TYPE_EXISTS: *val = 1; break; case BPF_CORE_TYPE_SIZE: sz = btf__resolve_size(spec->btf, spec->root_type_id); if (sz < 0) return -EINVAL; *val = sz; break; case BPF_CORE_TYPE_ID_LOCAL: /* BPF_CORE_TYPE_ID_LOCAL is handled specially and shouldn't get here */ default: return -EOPNOTSUPP; } return 0; } static int bpf_core_calc_enumval_relo(const struct bpf_core_relo *relo, const struct bpf_core_spec *spec, __u32 *val) { const struct btf_type *t; const struct btf_enum *e; switch (relo->kind) { case BPF_CORE_ENUMVAL_EXISTS: *val = spec ? 1 : 0; break; case BPF_CORE_ENUMVAL_VALUE: if (!spec) return -EUCLEAN; /* request instruction poisoning */ t = btf_type_by_id(spec->btf, spec->spec[0].type_id); e = btf_enum(t) + spec->spec[0].idx; *val = e->val; break; default: return -EOPNOTSUPP; } return 0; } /* Calculate original and target relocation values, given local and target * specs and relocation kind. These values are calculated for each candidate. * If there are multiple candidates, resulting values should all be consistent * with each other. Otherwise, libbpf will refuse to proceed due to ambiguity. * If instruction has to be poisoned, *poison will be set to true. */ static int bpf_core_calc_relo(const char *prog_name, const struct bpf_core_relo *relo, int relo_idx, const struct bpf_core_spec *local_spec, const struct bpf_core_spec *targ_spec, struct bpf_core_relo_res *res) { int err = -EOPNOTSUPP; res->orig_val = 0; res->new_val = 0; res->poison = false; res->validate = true; res->fail_memsz_adjust = false; res->orig_sz = res->new_sz = 0; res->orig_type_id = res->new_type_id = 0; if (core_relo_is_field_based(relo->kind)) { err = bpf_core_calc_field_relo(prog_name, relo, local_spec, &res->orig_val, &res->orig_sz, &res->orig_type_id, &res->validate); err = err ?: bpf_core_calc_field_relo(prog_name, relo, targ_spec, &res->new_val, &res->new_sz, &res->new_type_id, NULL); if (err) goto done; /* Validate if it's safe to adjust load/store memory size. * Adjustments are performed only if original and new memory * sizes differ. */ res->fail_memsz_adjust = false; if (res->orig_sz != res->new_sz) { const struct btf_type *orig_t, *new_t; orig_t = btf_type_by_id(local_spec->btf, res->orig_type_id); new_t = btf_type_by_id(targ_spec->btf, res->new_type_id); /* There are two use cases in which it's safe to * adjust load/store's mem size: * - reading a 32-bit kernel pointer, while on BPF * size pointers are always 64-bit; in this case * it's safe to "downsize" instruction size due to * pointer being treated as unsigned integer with * zero-extended upper 32-bits; * - reading unsigned integers, again due to * zero-extension is preserving the value correctly. * * In all other cases it's incorrect to attempt to * load/store field because read value will be * incorrect, so we poison relocated instruction. */ if (btf_is_ptr(orig_t) && btf_is_ptr(new_t)) goto done; if (btf_is_int(orig_t) && btf_is_int(new_t) && btf_int_encoding(orig_t) != BTF_INT_SIGNED && btf_int_encoding(new_t) != BTF_INT_SIGNED) goto done; /* mark as invalid mem size adjustment, but this will * only be checked for LDX/STX/ST insns */ res->fail_memsz_adjust = true; } } else if (core_relo_is_type_based(relo->kind)) { err = bpf_core_calc_type_relo(relo, local_spec, &res->orig_val, &res->validate); err = err ?: bpf_core_calc_type_relo(relo, targ_spec, &res->new_val, NULL); } else if (core_relo_is_enumval_based(relo->kind)) { err = bpf_core_calc_enumval_relo(relo, local_spec, &res->orig_val); err = err ?: bpf_core_calc_enumval_relo(relo, targ_spec, &res->new_val); } done: if (err == -EUCLEAN) { /* EUCLEAN is used to signal instruction poisoning request */ res->poison = true; err = 0; } else if (err == -EOPNOTSUPP) { /* EOPNOTSUPP means unknown/unsupported relocation */ pr_warn("prog '%s': relo #%d: unrecognized CO-RE relocation %s (%d) at insn #%d\n", prog_name, relo_idx, core_relo_kind_str(relo->kind), relo->kind, relo->insn_off / 8); } return err; } /* * Turn instruction for which CO_RE relocation failed into invalid one with * distinct signature. */ static void bpf_core_poison_insn(const char *prog_name, int relo_idx, int insn_idx, struct bpf_insn *insn) { pr_debug("prog '%s': relo #%d: substituting insn #%d w/ invalid insn\n", prog_name, relo_idx, insn_idx); insn->code = BPF_JMP | BPF_CALL; insn->dst_reg = 0; insn->src_reg = 0; insn->off = 0; /* if this instruction is reachable (not a dead code), * verifier will complain with the following message: * invalid func unknown#195896080 */ insn->imm = 195896080; /* => 0xbad2310 => "bad relo" */ } static int insn_bpf_size_to_bytes(struct bpf_insn *insn) { switch (BPF_SIZE(insn->code)) { case BPF_DW: return 8; case BPF_W: return 4; case BPF_H: return 2; case BPF_B: return 1; default: return -1; } } static int insn_bytes_to_bpf_size(__u32 sz) { switch (sz) { case 8: return BPF_DW; case 4: return BPF_W; case 2: return BPF_H; case 1: return BPF_B; default: return -1; } } /* * Patch relocatable BPF instruction. * * Patched value is determined by relocation kind and target specification. * For existence relocations target spec will be NULL if field/type is not found. * Expected insn->imm value is determined using relocation kind and local * spec, and is checked before patching instruction. If actual insn->imm value * is wrong, bail out with error. * * Currently supported classes of BPF instruction are: * 1. rX = (assignment with immediate operand); * 2. rX += (arithmetic operations with immediate operand); * 3. rX = (load with 64-bit immediate value); * 4. rX = *(T *)(rY + ), where T is one of {u8, u16, u32, u64}; * 5. *(T *)(rX + ) = rY, where T is one of {u8, u16, u32, u64}; * 6. *(T *)(rX + ) = , where T is one of {u8, u16, u32, u64}. */ int bpf_core_patch_insn(const char *prog_name, struct bpf_insn *insn, int insn_idx, const struct bpf_core_relo *relo, int relo_idx, const struct bpf_core_relo_res *res) { __u32 orig_val, new_val; __u8 class; class = BPF_CLASS(insn->code); if (res->poison) { poison: /* poison second part of ldimm64 to avoid confusing error from * verifier about "unknown opcode 00" */ if (is_ldimm64_insn(insn)) bpf_core_poison_insn(prog_name, relo_idx, insn_idx + 1, insn + 1); bpf_core_poison_insn(prog_name, relo_idx, insn_idx, insn); return 0; } orig_val = res->orig_val; new_val = res->new_val; switch (class) { case BPF_ALU: case BPF_ALU64: if (BPF_SRC(insn->code) != BPF_K) return -EINVAL; if (res->validate && insn->imm != orig_val) { pr_warn("prog '%s': relo #%d: unexpected insn #%d (ALU/ALU64) value: got %u, exp %u -> %u\n", prog_name, relo_idx, insn_idx, insn->imm, orig_val, new_val); return -EINVAL; } orig_val = insn->imm; insn->imm = new_val; pr_debug("prog '%s': relo #%d: patched insn #%d (ALU/ALU64) imm %u -> %u\n", prog_name, relo_idx, insn_idx, orig_val, new_val); break; case BPF_LDX: case BPF_ST: case BPF_STX: if (res->validate && insn->off != orig_val) { pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDX/ST/STX) value: got %u, exp %u -> %u\n", prog_name, relo_idx, insn_idx, insn->off, orig_val, new_val); return -EINVAL; } if (new_val > SHRT_MAX) { pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) value too big: %u\n", prog_name, relo_idx, insn_idx, new_val); return -ERANGE; } if (res->fail_memsz_adjust) { pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) accesses field incorrectly. " "Make sure you are accessing pointers, unsigned integers, or fields of matching type and size.\n", prog_name, relo_idx, insn_idx); goto poison; } orig_val = insn->off; insn->off = new_val; pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) off %u -> %u\n", prog_name, relo_idx, insn_idx, orig_val, new_val); if (res->new_sz != res->orig_sz) { int insn_bytes_sz, insn_bpf_sz; insn_bytes_sz = insn_bpf_size_to_bytes(insn); if (insn_bytes_sz != res->orig_sz) { pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) unexpected mem size: got %d, exp %u\n", prog_name, relo_idx, insn_idx, insn_bytes_sz, res->orig_sz); return -EINVAL; } insn_bpf_sz = insn_bytes_to_bpf_size(res->new_sz); if (insn_bpf_sz < 0) { pr_warn("prog '%s': relo #%d: insn #%d (LDX/ST/STX) invalid new mem size: %u\n", prog_name, relo_idx, insn_idx, res->new_sz); return -EINVAL; } insn->code = BPF_MODE(insn->code) | insn_bpf_sz | BPF_CLASS(insn->code); pr_debug("prog '%s': relo #%d: patched insn #%d (LDX/ST/STX) mem_sz %u -> %u\n", prog_name, relo_idx, insn_idx, res->orig_sz, res->new_sz); } break; case BPF_LD: { __u64 imm; if (!is_ldimm64_insn(insn) || insn[0].src_reg != 0 || insn[0].off != 0 || insn[1].code != 0 || insn[1].dst_reg != 0 || insn[1].src_reg != 0 || insn[1].off != 0) { pr_warn("prog '%s': relo #%d: insn #%d (LDIMM64) has unexpected form\n", prog_name, relo_idx, insn_idx); return -EINVAL; } imm = insn[0].imm + ((__u64)insn[1].imm << 32); if (res->validate && imm != orig_val) { pr_warn("prog '%s': relo #%d: unexpected insn #%d (LDIMM64) value: got %llu, exp %u -> %u\n", prog_name, relo_idx, insn_idx, (unsigned long long)imm, orig_val, new_val); return -EINVAL; } insn[0].imm = new_val; insn[1].imm = 0; /* currently only 32-bit values are supported */ pr_debug("prog '%s': relo #%d: patched insn #%d (LDIMM64) imm64 %llu -> %u\n", prog_name, relo_idx, insn_idx, (unsigned long long)imm, new_val); break; } default: pr_warn("prog '%s': relo #%d: trying to relocate unrecognized insn #%d, code:0x%x, src:0x%x, dst:0x%x, off:0x%x, imm:0x%x\n", prog_name, relo_idx, insn_idx, insn->code, insn->src_reg, insn->dst_reg, insn->off, insn->imm); return -EINVAL; } return 0; } /* Output spec definition in the format: * [] () + => @, * where is a C-syntax view of recorded field access, e.g.: x.a[3].b */ static void bpf_core_dump_spec(const char *prog_name, int level, const struct bpf_core_spec *spec) { const struct btf_type *t; const struct btf_enum *e; const char *s; __u32 type_id; int i; type_id = spec->root_type_id; t = btf_type_by_id(spec->btf, type_id); s = btf__name_by_offset(spec->btf, t->name_off); libbpf_print(level, "[%u] %s %s", type_id, btf_kind_str(t), str_is_empty(s) ? "" : s); if (core_relo_is_type_based(spec->relo_kind)) return; if (core_relo_is_enumval_based(spec->relo_kind)) { t = skip_mods_and_typedefs(spec->btf, type_id, NULL); e = btf_enum(t) + spec->raw_spec[0]; s = btf__name_by_offset(spec->btf, e->name_off); libbpf_print(level, "::%s = %u", s, e->val); return; } if (core_relo_is_field_based(spec->relo_kind)) { for (i = 0; i < spec->len; i++) { if (spec->spec[i].name) libbpf_print(level, ".%s", spec->spec[i].name); else if (i > 0 || spec->spec[i].idx > 0) libbpf_print(level, "[%u]", spec->spec[i].idx); } libbpf_print(level, " ("); for (i = 0; i < spec->raw_len; i++) libbpf_print(level, "%s%d", i == 0 ? "" : ":", spec->raw_spec[i]); if (spec->bit_offset % 8) libbpf_print(level, " @ offset %u.%u)", spec->bit_offset / 8, spec->bit_offset % 8); else libbpf_print(level, " @ offset %u)", spec->bit_offset / 8); return; } } /* * Calculate CO-RE relocation target result. * * The outline and important points of the algorithm: * 1. For given local type, find corresponding candidate target types. * Candidate type is a type with the same "essential" name, ignoring * everything after last triple underscore (___). E.g., `sample`, * `sample___flavor_one`, `sample___flavor_another_one`, are all candidates * for each other. Names with triple underscore are referred to as * "flavors" and are useful, among other things, to allow to * specify/support incompatible variations of the same kernel struct, which * might differ between different kernel versions and/or build * configurations. * * N.B. Struct "flavors" could be generated by bpftool's BTF-to-C * converter, when deduplicated BTF of a kernel still contains more than * one different types with the same name. In that case, ___2, ___3, etc * are appended starting from second name conflict. But start flavors are * also useful to be defined "locally", in BPF program, to extract same * data from incompatible changes between different kernel * versions/configurations. For instance, to handle field renames between * kernel versions, one can use two flavors of the struct name with the * same common name and use conditional relocations to extract that field, * depending on target kernel version. * 2. For each candidate type, try to match local specification to this * candidate target type. Matching involves finding corresponding * high-level spec accessors, meaning that all named fields should match, * as well as all array accesses should be within the actual bounds. Also, * types should be compatible (see bpf_core_fields_are_compat for details). * 3. It is supported and expected that there might be multiple flavors * matching the spec. As long as all the specs resolve to the same set of * offsets across all candidates, there is no error. If there is any * ambiguity, CO-RE relocation will fail. This is necessary to accomodate * imprefection of BTF deduplication, which can cause slight duplication of * the same BTF type, if some directly or indirectly referenced (by * pointer) type gets resolved to different actual types in different * object files. If such situation occurs, deduplicated BTF will end up * with two (or more) structurally identical types, which differ only in * types they refer to through pointer. This should be OK in most cases and * is not an error. * 4. Candidate types search is performed by linearly scanning through all * types in target BTF. It is anticipated that this is overall more * efficient memory-wise and not significantly worse (if not better) * CPU-wise compared to prebuilding a map from all local type names to * a list of candidate type names. It's also sped up by caching resolved * list of matching candidates per each local "root" type ID, that has at * least one bpf_core_relo associated with it. This list is shared * between multiple relocations for the same type ID and is updated as some * of the candidates are pruned due to structural incompatibility. */ int bpf_core_calc_relo_insn(const char *prog_name, const struct bpf_core_relo *relo, int relo_idx, const struct btf *local_btf, struct bpf_core_cand_list *cands, struct bpf_core_spec *specs_scratch, struct bpf_core_relo_res *targ_res) { struct bpf_core_spec *local_spec = &specs_scratch[0]; struct bpf_core_spec *cand_spec = &specs_scratch[1]; struct bpf_core_spec *targ_spec = &specs_scratch[2]; struct bpf_core_relo_res cand_res; const struct btf_type *local_type; const char *local_name; __u32 local_id; const char *spec_str; int i, j, err; local_id = relo->type_id; local_type = btf_type_by_id(local_btf, local_id); local_name = btf__name_by_offset(local_btf, local_type->name_off); if (!local_name) return -EINVAL; spec_str = btf__name_by_offset(local_btf, relo->access_str_off); if (str_is_empty(spec_str)) return -EINVAL; err = bpf_core_parse_spec(prog_name, local_btf, local_id, spec_str, relo->kind, local_spec); if (err) { pr_warn("prog '%s': relo #%d: parsing [%d] %s %s + %s failed: %d\n", prog_name, relo_idx, local_id, btf_kind_str(local_type), str_is_empty(local_name) ? "" : local_name, spec_str, err); return -EINVAL; } pr_debug("prog '%s': relo #%d: kind <%s> (%d), spec is ", prog_name, relo_idx, core_relo_kind_str(relo->kind), relo->kind); bpf_core_dump_spec(prog_name, LIBBPF_DEBUG, local_spec); libbpf_print(LIBBPF_DEBUG, "\n"); /* TYPE_ID_LOCAL relo is special and doesn't need candidate search */ if (relo->kind == BPF_CORE_TYPE_ID_LOCAL) { /* bpf_insn's imm value could get out of sync during linking */ memset(targ_res, 0, sizeof(*targ_res)); targ_res->validate = false; targ_res->poison = false; targ_res->orig_val = local_spec->root_type_id; targ_res->new_val = local_spec->root_type_id; return 0; } /* libbpf doesn't support candidate search for anonymous types */ if (str_is_empty(local_name)) { pr_warn("prog '%s': relo #%d: <%s> (%d) relocation doesn't support anonymous types\n", prog_name, relo_idx, core_relo_kind_str(relo->kind), relo->kind); return -EOPNOTSUPP; } for (i = 0, j = 0; i < cands->len; i++) { err = bpf_core_spec_match(local_spec, cands->cands[i].btf, cands->cands[i].id, cand_spec); if (err < 0) { pr_warn("prog '%s': relo #%d: error matching candidate #%d ", prog_name, relo_idx, i); bpf_core_dump_spec(prog_name, LIBBPF_WARN, cand_spec); libbpf_print(LIBBPF_WARN, ": %d\n", err); return err; } pr_debug("prog '%s': relo #%d: %s candidate #%d ", prog_name, relo_idx, err == 0 ? "non-matching" : "matching", i); bpf_core_dump_spec(prog_name, LIBBPF_DEBUG, cand_spec); libbpf_print(LIBBPF_DEBUG, "\n"); if (err == 0) continue; err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, cand_spec, &cand_res); if (err) return err; if (j == 0) { *targ_res = cand_res; *targ_spec = *cand_spec; } else if (cand_spec->bit_offset != targ_spec->bit_offset) { /* if there are many field relo candidates, they * should all resolve to the same bit offset */ pr_warn("prog '%s': relo #%d: field offset ambiguity: %u != %u\n", prog_name, relo_idx, cand_spec->bit_offset, targ_spec->bit_offset); return -EINVAL; } else if (cand_res.poison != targ_res->poison || cand_res.new_val != targ_res->new_val) { /* all candidates should result in the same relocation * decision and value, otherwise it's dangerous to * proceed due to ambiguity */ pr_warn("prog '%s': relo #%d: relocation decision ambiguity: %s %u != %s %u\n", prog_name, relo_idx, cand_res.poison ? "failure" : "success", cand_res.new_val, targ_res->poison ? "failure" : "success", targ_res->new_val); return -EINVAL; } cands->cands[j++] = cands->cands[i]; } /* * For BPF_CORE_FIELD_EXISTS relo or when used BPF program has field * existence checks or kernel version/config checks, it's expected * that we might not find any candidates. In this case, if field * wasn't found in any candidate, the list of candidates shouldn't * change at all, we'll just handle relocating appropriately, * depending on relo's kind. */ if (j > 0) cands->len = j; /* * If no candidates were found, it might be both a programmer error, * as well as expected case, depending whether instruction w/ * relocation is guarded in some way that makes it unreachable (dead * code) if relocation can't be resolved. This is handled in * bpf_core_patch_insn() uniformly by replacing that instruction with * BPF helper call insn (using invalid helper ID). If that instruction * is indeed unreachable, then it will be ignored and eliminated by * verifier. If it was an error, then verifier will complain and point * to a specific instruction number in its log. */ if (j == 0) { pr_debug("prog '%s': relo #%d: no matching targets found\n", prog_name, relo_idx); /* calculate single target relo result explicitly */ err = bpf_core_calc_relo(prog_name, relo, relo_idx, local_spec, NULL, targ_res); if (err) return err; } return 0; }