libbpf: Implement type-based CO-RE relocations support
Implement support for TYPE_EXISTS/TYPE_SIZE/TYPE_ID_LOCAL/TYPE_ID_REMOTE relocations. These are examples of type-based relocations, as opposed to field-based relocations supported already. The difference is that they are calculating relocation values based on the type itself, not a field within a struct/union. Type-based relos have slightly different semantics when matching local types to kernel target types, see comments in bpf_core_types_are_compat() for details. Their behavior on failure to find target type in kernel BTF also differs. Instead of "poisoning" relocatable instruction and failing load subsequently in kernel, they return 0 (which is rarely a valid return result, so user BPF code can use that to detect success/failure of the relocation and deal with it without extra "guarding" relocations). Also, it's always possible to check existence of the type in target kernel with TYPE_EXISTS relocation, similarly to a field-based FIELD_EXISTS. TYPE_ID_LOCAL relocation is a bit special in that it always succeeds (barring any libbpf/Clang bugs) and resolved to BTF ID using **local** BTF info of BPF program itself. Tests in subsequent patches demonstrate the usage and semantics of new relocations. Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20200819194519.3375898-2-andriin@fb.com
This commit is contained in:
Andrii Nakryiko
Alexei Starovoitov
Родитель
defcffeb51
Коммит
3fc32f40c4
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@ -19,6 +19,18 @@ enum bpf_field_info_kind {
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BPF_FIELD_RSHIFT_U64 = 5,
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};
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/* second argument to __builtin_btf_type_id() built-in */
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enum bpf_type_id_kind {
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BPF_TYPE_ID_LOCAL = 0, /* BTF type ID in local program */
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BPF_TYPE_ID_TARGET = 1, /* BTF type ID in target kernel */
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};
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/* second argument to __builtin_preserve_type_info() built-in */
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enum bpf_type_info_kind {
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BPF_TYPE_EXISTS = 0, /* type existence in target kernel */
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BPF_TYPE_SIZE = 1, /* type size in target kernel */
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};
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#define __CORE_RELO(src, field, info) \
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__builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
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@ -94,12 +106,50 @@ enum bpf_field_info_kind {
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__builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
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/*
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* Convenience macro to get byte size of a field. Works for integers,
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* Convenience macro to get the byte size of a field. Works for integers,
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* struct/unions, pointers, arrays, and enums.
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*/
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#define bpf_core_field_size(field) \
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__builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
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/*
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* Convenience macro to get BTF type ID of a specified type, using a local BTF
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* information. Return 32-bit unsigned integer with type ID from program's own
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* BTF. Always succeeds.
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*/
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#define bpf_core_type_id_local(type) \
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__builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_LOCAL)
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/*
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* Convenience macro to get BTF type ID of a target kernel's type that matches
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* specified local type.
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* Returns:
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* - valid 32-bit unsigned type ID in kernel BTF;
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* - 0, if no matching type was found in a target kernel BTF.
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*/
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#define bpf_core_type_id_kernel(type) \
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__builtin_btf_type_id(*(typeof(type) *)0, BPF_TYPE_ID_TARGET)
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/*
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* Convenience macro to check that provided named type
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* (struct/union/enum/typedef) exists in a target kernel.
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* Returns:
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* 1, if such type is present in target kernel's BTF;
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* 0, if no matching type is found.
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*/
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#define bpf_core_type_exists(type) \
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__builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_EXISTS)
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/*
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* Convenience macro to get the byte size of a provided named type
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* (struct/union/enum/typedef) in a target kernel.
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* Returns:
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* >= 0 size (in bytes), if type is present in target kernel's BTF;
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* 0, if no matching type is found.
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*/
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#define bpf_core_type_size(type) \
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__builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_SIZE)
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/*
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* bpf_core_read() abstracts away bpf_probe_read_kernel() call and captures
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* offset relocation for source address using __builtin_preserve_access_index()
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@ -4111,6 +4111,10 @@ static const char *core_relo_kind_str(enum bpf_core_relo_kind kind)
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case BPF_FIELD_SIGNED: return "signed";
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case BPF_FIELD_LSHIFT_U64: return "lshift_u64";
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case BPF_FIELD_RSHIFT_U64: return "rshift_u64";
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case BPF_TYPE_ID_LOCAL: return "local_type_id";
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case BPF_TYPE_ID_TARGET: return "target_type_id";
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case BPF_TYPE_EXISTS: return "type_exists";
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case BPF_TYPE_SIZE: return "type_size";
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default: return "unknown";
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}
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}
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@ -4130,6 +4134,19 @@ static bool core_relo_is_field_based(enum bpf_core_relo_kind kind)
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}
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}
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static bool core_relo_is_type_based(enum bpf_core_relo_kind kind)
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{
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switch (kind) {
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case BPF_TYPE_ID_LOCAL:
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case BPF_TYPE_ID_TARGET:
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case BPF_TYPE_EXISTS:
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case BPF_TYPE_SIZE:
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return true;
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default:
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return false;
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}
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}
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/*
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* Turn bpf_core_relo into a low- and high-level spec representation,
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* validating correctness along the way, as well as calculating resulting
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@ -4160,6 +4177,9 @@ static bool core_relo_is_field_based(enum bpf_core_relo_kind kind)
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* - field 'a' access (corresponds to '2' in low-level spec);
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* - array element #3 access (corresponds to '3' in low-level spec).
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*
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* Type-based relocations (TYPE_EXISTS/TYPE_SIZE,
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* TYPE_ID_LOCAL/TYPE_ID_TARGET) don't capture any field information. Their
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* spec and raw_spec are kept empty.
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*/
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static int bpf_core_parse_spec(const struct btf *btf,
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__u32 type_id,
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@ -4182,6 +4202,13 @@ static int bpf_core_parse_spec(const struct btf *btf,
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spec->root_type_id = type_id;
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spec->relo_kind = relo_kind;
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/* type-based relocations don't have a field access string */
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if (core_relo_is_type_based(relo_kind)) {
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if (strcmp(spec_str, "0"))
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return -EINVAL;
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return 0;
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}
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/* parse spec_str="0:1:2:3:4" into array raw_spec=[0, 1, 2, 3, 4] */
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while (*spec_str) {
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if (*spec_str == ':')
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@ -4317,7 +4344,7 @@ static struct ids_vec *bpf_core_find_cands(const struct btf *local_btf,
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const struct btf *targ_btf)
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{
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size_t local_essent_len, targ_essent_len;
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const char *local_name, *targ_name, *targ_kind;
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const char *local_name, *targ_name;
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const struct btf_type *t, *local_t;
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struct ids_vec *cand_ids;
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__u32 *new_ids;
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@ -4339,14 +4366,12 @@ static struct ids_vec *bpf_core_find_cands(const struct btf *local_btf,
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n = btf__get_nr_types(targ_btf);
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for (i = 1; i <= n; i++) {
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t = btf__type_by_id(targ_btf, i);
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if (btf_kind(t) != btf_kind(local_t))
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continue;
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targ_name = btf__name_by_offset(targ_btf, t->name_off);
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if (str_is_empty(targ_name))
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continue;
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targ_kind = btf_kind_str(t);
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t = skip_mods_and_typedefs(targ_btf, i, NULL);
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if (!btf_is_composite(t) && !btf_is_array(t))
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continue;
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targ_essent_len = bpf_core_essential_name_len(targ_name);
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if (targ_essent_len != local_essent_len)
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@ -4355,7 +4380,7 @@ static struct ids_vec *bpf_core_find_cands(const struct btf *local_btf,
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if (strncmp(local_name, targ_name, local_essent_len) == 0) {
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pr_debug("CO-RE relocating [%d] %s %s: found target candidate [%d] %s %s\n",
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local_type_id, btf_kind_str(local_t),
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local_name, i, targ_kind, targ_name);
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local_name, i, btf_kind_str(t), targ_name);
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new_ids = libbpf_reallocarray(cand_ids->data,
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cand_ids->len + 1,
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sizeof(*cand_ids->data));
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@ -4373,8 +4398,9 @@ err_out:
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return ERR_PTR(err);
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}
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/* Check two types for compatibility, skipping const/volatile/restrict and
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* typedefs, to ensure we are relocating compatible entities:
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/* Check two types for compatibility for the purpose of field access
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* relocation. const/volatile/restrict and typedefs are skipped to ensure we
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* are relocating semantically compatible entities:
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* - any two STRUCTs/UNIONs are compatible and can be mixed;
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* - any two FWDs are compatible, if their names match (modulo flavor suffix);
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* - any two PTRs are always compatible;
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@ -4529,6 +4555,100 @@ static int bpf_core_match_member(const struct btf *local_btf,
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return 0;
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}
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/* Check local and target types for compatibility. This check is used for
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* type-based CO-RE relocations and follow slightly different rules than
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* field-based relocations. This function assumes that root types were already
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* checked for name match. Beyond that initial root-level name check, names
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* are completely ignored. Compatibility rules are as follows:
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* - any two STRUCTs/UNIONs/FWDs/ENUMs/INTs are considered compatible, but
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* kind should match for local and target types (i.e., STRUCT is not
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* compatible with UNION);
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* - for ENUMs, the size is ignored;
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* - for INT, size and signedness are ignored;
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* - for ARRAY, dimensionality is ignored, element types are checked for
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* compatibility recursively;
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* - CONST/VOLATILE/RESTRICT modifiers are ignored;
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* - TYPEDEFs/PTRs are compatible if types they pointing to are compatible;
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* - FUNC_PROTOs are compatible if they have compatible signature: same
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* number of input args and compatible return and argument types.
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* These rules are not set in stone and probably will be adjusted as we get
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* more experience with using BPF CO-RE relocations.
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*/
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static int bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
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const struct btf *targ_btf, __u32 targ_id)
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{
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const struct btf_type *local_type, *targ_type;
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int depth = 32; /* max recursion depth */
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/* caller made sure that names match (ignoring flavor suffix) */
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local_type = btf__type_by_id(local_btf, local_id);
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targ_type = btf__type_by_id(local_btf, local_id);
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if (btf_kind(local_type) != btf_kind(targ_type))
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return 0;
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recur:
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depth--;
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if (depth < 0)
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return -EINVAL;
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local_type = skip_mods_and_typedefs(local_btf, local_id, &local_id);
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targ_type = skip_mods_and_typedefs(targ_btf, targ_id, &targ_id);
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if (!local_type || !targ_type)
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return -EINVAL;
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if (btf_kind(local_type) != btf_kind(targ_type))
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return 0;
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switch (btf_kind(local_type)) {
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case BTF_KIND_UNKN:
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case BTF_KIND_STRUCT:
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case BTF_KIND_UNION:
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case BTF_KIND_ENUM:
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case BTF_KIND_FWD:
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return 1;
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case BTF_KIND_INT:
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/* just reject deprecated bitfield-like integers; all other
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* integers are by default compatible between each other
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*/
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return btf_int_offset(local_type) == 0 && btf_int_offset(targ_type) == 0;
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case BTF_KIND_PTR:
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local_id = local_type->type;
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targ_id = targ_type->type;
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goto recur;
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case BTF_KIND_ARRAY:
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local_id = btf_array(local_type)->type;
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targ_id = btf_array(targ_type)->type;
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goto recur;
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case BTF_KIND_FUNC_PROTO: {
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struct btf_param *local_p = btf_params(local_type);
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struct btf_param *targ_p = btf_params(targ_type);
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__u16 local_vlen = btf_vlen(local_type);
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__u16 targ_vlen = btf_vlen(targ_type);
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int i, err;
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if (local_vlen != targ_vlen)
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return 0;
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for (i = 0; i < local_vlen; i++, local_p++, targ_p++) {
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skip_mods_and_typedefs(local_btf, local_p->type, &local_id);
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skip_mods_and_typedefs(targ_btf, targ_p->type, &targ_id);
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err = bpf_core_types_are_compat(local_btf, local_id, targ_btf, targ_id);
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if (err <= 0)
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return err;
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}
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/* tail recurse for return type check */
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skip_mods_and_typedefs(local_btf, local_type->type, &local_id);
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skip_mods_and_typedefs(targ_btf, targ_type->type, &targ_id);
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goto recur;
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}
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default:
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pr_warn("unexpected kind %s relocated, local [%d], target [%d]\n",
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btf_kind_str(local_type), local_id, targ_id);
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return 0;
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}
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}
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/*
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* Try to match local spec to a target type and, if successful, produce full
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* target spec (high-level, low-level + bit offset).
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@ -4547,6 +4667,12 @@ static int bpf_core_spec_match(struct bpf_core_spec *local_spec,
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targ_spec->root_type_id = targ_id;
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targ_spec->relo_kind = local_spec->relo_kind;
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if (core_relo_is_type_based(local_spec->relo_kind)) {
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return bpf_core_types_are_compat(local_spec->btf,
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local_spec->root_type_id,
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targ_btf, targ_id);
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}
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local_acc = &local_spec->spec[0];
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targ_acc = &targ_spec->spec[0];
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@ -4720,6 +4846,40 @@ static int bpf_core_calc_field_relo(const struct bpf_program *prog,
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return 0;
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}
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static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo,
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const struct bpf_core_spec *spec,
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__u32 *val)
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{
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__s64 sz;
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/* type-based relos return zero when target type is not found */
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if (!spec) {
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*val = 0;
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return 0;
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}
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switch (relo->kind) {
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case BPF_TYPE_ID_TARGET:
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*val = spec->root_type_id;
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break;
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case BPF_TYPE_EXISTS:
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*val = 1;
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break;
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case BPF_TYPE_SIZE:
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sz = btf__resolve_size(spec->btf, spec->root_type_id);
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if (sz < 0)
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return -EINVAL;
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*val = sz;
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break;
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case BPF_TYPE_ID_LOCAL:
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/* BPF_TYPE_ID_LOCAL is handled specially and shouldn't get here */
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default:
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return -EOPNOTSUPP;
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}
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return 0;
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}
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struct bpf_core_relo_res
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{
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/* expected value in the instruction, unless validate == false */
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@ -4755,6 +4915,9 @@ static int bpf_core_calc_relo(const struct bpf_program *prog,
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if (core_relo_is_field_based(relo->kind)) {
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err = bpf_core_calc_field_relo(prog, relo, local_spec, &res->orig_val, &res->validate);
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err = err ?: bpf_core_calc_field_relo(prog, relo, targ_spec, &res->new_val, NULL);
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} else if (core_relo_is_type_based(relo->kind)) {
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err = bpf_core_calc_type_relo(relo, local_spec, &res->orig_val);
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err = err ?: bpf_core_calc_type_relo(relo, targ_spec, &res->new_val);
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}
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if (err == -EUCLEAN) {
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@ -4894,6 +5057,9 @@ static void bpf_core_dump_spec(int level, const struct bpf_core_spec *spec)
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libbpf_print(level, "[%u] %s %s", type_id, btf_kind_str(t), str_is_empty(s) ? "<anon>" : s);
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if (core_relo_is_type_based(spec->relo_kind))
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return;
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if (core_relo_is_field_based(spec->relo_kind)) {
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for (i = 0; i < spec->len; i++) {
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if (spec->spec[i].name)
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|
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@ -4911,6 +5077,7 @@ static void bpf_core_dump_spec(int level, const struct bpf_core_spec *spec)
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spec->bit_offset / 8, spec->bit_offset % 8);
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else
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libbpf_print(level, " @ offset %u)", spec->bit_offset / 8);
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return;
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}
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}
|
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|
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@ -4979,7 +5146,7 @@ static void *u32_as_hash_key(__u32 x)
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* between multiple relocations for the same type ID and is updated as some
|
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* of the candidates are pruned due to structural incompatibility.
|
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*/
|
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static int bpf_core_reloc_field(struct bpf_program *prog,
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static int bpf_core_apply_relo(struct bpf_program *prog,
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const struct bpf_core_relo *relo,
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int relo_idx,
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const struct btf *local_btf,
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|
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@ -5003,7 +5170,7 @@ static int bpf_core_reloc_field(struct bpf_program *prog,
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return -EINVAL;
|
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|
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local_name = btf__name_by_offset(local_btf, local_type->name_off);
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if (str_is_empty(local_name))
|
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if (!local_name)
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return -EINVAL;
|
||||
|
||||
spec_str = btf__name_by_offset(local_btf, relo->access_str_off);
|
||||
|
|
@ -5014,7 +5181,8 @@ static int bpf_core_reloc_field(struct bpf_program *prog,
|
|||
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),
|
||||
local_name, spec_str, err);
|
||||
str_is_empty(local_name) ? "<anon>" : local_name,
|
||||
spec_str, err);
|
||||
return -EINVAL;
|
||||
}
|
||||
|
||||
|
|
@ -5023,12 +5191,28 @@ static int bpf_core_reloc_field(struct bpf_program *prog,
|
|||
bpf_core_dump_spec(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_TYPE_ID_LOCAL) {
|
||||
targ_res.validate = true;
|
||||
targ_res.poison = false;
|
||||
targ_res.orig_val = local_spec.root_type_id;
|
||||
targ_res.new_val = local_spec.root_type_id;
|
||||
goto patch_insn;
|
||||
}
|
||||
|
||||
/* libbpf doesn't support candidate search for anonymous types */
|
||||
if (str_is_empty(spec_str)) {
|
||||
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;
|
||||
}
|
||||
|
||||
if (!hashmap__find(cand_cache, type_key, (void **)&cand_ids)) {
|
||||
cand_ids = bpf_core_find_cands(local_btf, local_id, targ_btf);
|
||||
if (IS_ERR(cand_ids)) {
|
||||
pr_warn("prog '%s': relo #%d: target candidate search failed for [%d] %s %s: %ld",
|
||||
prog_name, relo_idx, local_id, btf_kind_str(local_type), local_name,
|
||||
PTR_ERR(cand_ids));
|
||||
prog_name, relo_idx, local_id, btf_kind_str(local_type),
|
||||
local_name, PTR_ERR(cand_ids));
|
||||
return PTR_ERR(cand_ids);
|
||||
}
|
||||
err = hashmap__set(cand_cache, type_key, cand_ids, NULL, NULL);
|
||||
|
|
@ -5084,7 +5268,7 @@ static int bpf_core_reloc_field(struct bpf_program *prog,
|
|||
return -EINVAL;
|
||||
}
|
||||
|
||||
cand_ids->data[j++] = cand_spec.spec[0].type_id;
|
||||
cand_ids->data[j++] = cand_spec.root_type_id;
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
@ -5103,7 +5287,7 @@ static int bpf_core_reloc_field(struct bpf_program *prog,
|
|||
* 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_reloc_insn() uniformly by replacing that instruction with
|
||||
* 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
|
||||
|
|
@ -5119,6 +5303,7 @@ static int bpf_core_reloc_field(struct bpf_program *prog,
|
|||
return err;
|
||||
}
|
||||
|
||||
patch_insn:
|
||||
/* bpf_core_patch_insn() should know how to handle missing targ_spec */
|
||||
err = bpf_core_patch_insn(prog, relo, relo_idx, &targ_res);
|
||||
if (err) {
|
||||
|
|
@ -5186,7 +5371,7 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
|
|||
sec_name, sec->num_info);
|
||||
|
||||
for_each_btf_ext_rec(seg, sec, i, rec) {
|
||||
err = bpf_core_reloc_field(prog, rec, i, obj->btf,
|
||||
err = bpf_core_apply_relo(prog, rec, i, obj->btf,
|
||||
targ_btf, cand_cache);
|
||||
if (err) {
|
||||
pr_warn("prog '%s': relo #%d: failed to relocate: %d\n",
|
||||
|
|
|
|||
|
|
@ -238,6 +238,10 @@ enum bpf_core_relo_kind {
|
|||
BPF_FIELD_SIGNED = 3, /* field signedness (0 - unsigned, 1 - signed) */
|
||||
BPF_FIELD_LSHIFT_U64 = 4, /* bitfield-specific left bitshift */
|
||||
BPF_FIELD_RSHIFT_U64 = 5, /* bitfield-specific right bitshift */
|
||||
BPF_TYPE_ID_LOCAL = 6, /* type ID in local BPF object */
|
||||
BPF_TYPE_ID_TARGET = 7, /* type ID in target kernel */
|
||||
BPF_TYPE_EXISTS = 8, /* type existence in target kernel */
|
||||
BPF_TYPE_SIZE = 9, /* type size in bytes */
|
||||
};
|
||||
|
||||
/* The minimum bpf_core_relo checked by the loader
|
||||
|
|
|
|||
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Ссылка в новой задаче