diff options
| author | Andrii Nakryiko <andrii@kernel.org> | 2021-12-13 04:07:06 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2021-12-13 04:26:24 +0300 |
| commit | 4b443bc1785f28df56fdbd6a107dc68ef7d5aa8e (patch) | |
| tree | 2c6e46dbfaff8bce7a0c22d5f067aac442f70480 /tools/lib | |
| parent | f12468828c28ff90d20c99b234a94223401f7924 (diff) | |
| download | linux-4b443bc1785f28df56fdbd6a107dc68ef7d5aa8e.tar.xz | |
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
Diffstat (limited to 'tools/lib')
| -rw-r--r-- | tools/lib/bpf/relo_core.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/tools/lib/bpf/relo_core.c b/tools/lib/bpf/relo_core.c index 32464f0ab4b1..c770483b4c36 100644 --- a/tools/lib/bpf/relo_core.c +++ b/tools/lib/bpf/relo_core.c @@ -709,10 +709,14 @@ static int bpf_core_calc_field_relo(const char *prog_name, static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo, const struct bpf_core_spec *spec, - __u32 *val) + __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; @@ -722,6 +726,11 @@ static int bpf_core_calc_type_relo(const struct bpf_core_relo *relo, 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; @@ -861,8 +870,8 @@ static int bpf_core_calc_relo(const char *prog_name, 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); - err = err ?: bpf_core_calc_type_relo(relo, targ_spec, &res->new_val); + 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); @@ -1213,7 +1222,8 @@ int bpf_core_apply_relo_insn(const char *prog_name, struct bpf_insn *insn, /* TYPE_ID_LOCAL relo is special and doesn't need candidate search */ if (relo->kind == BPF_CORE_TYPE_ID_LOCAL) { - targ_res.validate = true; + /* bpf_insn's imm value could get out of sync during linking */ + 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; @@ -1227,7 +1237,6 @@ int bpf_core_apply_relo_insn(const char *prog_name, struct bpf_insn *insn, 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); |