From: Andrii Nakryiko <andrii@kernel.org>
Date: Sun, 12 Dec 2021 17:07:06 -0800
Subject: libbpf: Don't validate TYPE_ID relo's original imm value
Patch-mainline: v5.17-rc1
Git-commit: 4b443bc1785f28df56fdbd6a107dc68ef7d5aa8e
References: jsc#PED-1377
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
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
tools/lib/bpf/relo_core.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
--- 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(cons
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
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
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
/* 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
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);