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libbpf: Don't validate TYPE_ID relo's original imm value
During linking, type IDs in the resulting linked BPF object file can change, and so ldimm64 instructions corresponding to BPF_CORE_TYPE_ID_TARGET and BPF_CORE_TYPE_ID_LOCAL CO-RE relos can get their imm value out of sync with actual CO-RE relocation information that's updated by BPF linker properly during linking process. We could teach BPF linker to adjust such instructions, but it feels a bit too much for linker to re-implement good chunk of bpf_core_patch_insns logic just for this. This is a redundant safety check for TYPE_ID relocations, as the real validation is in matching CO-RE specs, so if that works fine, it's very unlikely that there is something wrong with the instruction itself. So, instead, teach libbpf (and kernel) to ignore insn->imm for BPF_CORE_TYPE_ID_TARGET and BPF_CORE_TYPE_ID_LOCAL relos. Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211213010706.100231-1-andrii@kernel.org
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@ -709,10 +709,14 @@ static int bpf_core_calc_field_relo(const char *prog_name,
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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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__u32 *val, bool *validate)
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{
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__s64 sz;
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/* by default, always check expected value in bpf_insn */
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if (validate)
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*validate = true;
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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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@ -722,6 +726,11 @@ static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo,
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switch (relo->kind) {
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case BPF_CORE_TYPE_ID_TARGET:
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*val = spec->root_type_id;
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/* type ID, embedded in bpf_insn, might change during linking,
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* so enforcing it is pointless
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*/
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if (validate)
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*validate = false;
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break;
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case BPF_CORE_TYPE_EXISTS:
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*val = 1;
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@ -861,8 +870,8 @@ static int bpf_core_calc_relo(const char *prog_name,
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res->fail_memsz_adjust = true;
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}
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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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err = bpf_core_calc_type_relo(relo, local_spec, &res->orig_val, &res->validate);
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err = err ?: bpf_core_calc_type_relo(relo, targ_spec, &res->new_val, NULL);
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} else if (core_relo_is_enumval_based(relo->kind)) {
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err = bpf_core_calc_enumval_relo(relo, local_spec, &res->orig_val);
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err = err ?: bpf_core_calc_enumval_relo(relo, targ_spec, &res->new_val);
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@ -1213,7 +1222,8 @@ int bpf_core_apply_relo_insn(const char *prog_name, struct bpf_insn *insn,
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/* TYPE_ID_LOCAL relo is special and doesn't need candidate search */
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if (relo->kind == BPF_CORE_TYPE_ID_LOCAL) {
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targ_res.validate = true;
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/* bpf_insn's imm value could get out of sync during linking */
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targ_res.validate = false;
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targ_res.poison = false;
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targ_res.orig_val = local_spec->root_type_id;
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targ_res.new_val = local_spec->root_type_id;
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@ -1227,7 +1237,6 @@ int bpf_core_apply_relo_insn(const char *prog_name, struct bpf_insn *insn,
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return -EOPNOTSUPP;
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}
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for (i = 0, j = 0; i < cands->len; i++) {
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err = bpf_core_spec_match(local_spec, cands->cands[i].btf,
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cands->cands[i].id, cand_spec);
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