* [PATCH bpf v2 1/2] btf: fix resolving BTF_KIND_VAR after ARRAY, STRUCT, UNION, PTR
[not found] <20230306112138.155352-1-lmb@isovalent.com>
@ 2023-03-06 11:21 ` Lorenz Bauer
2023-03-06 22:19 ` Daniel Borkmann
2023-03-06 11:21 ` [PATCH bpf v2 2/2] selftests/bpf: check that modifier resolves after pointer Lorenz Bauer
1 sibling, 1 reply; 3+ messages in thread
From: Lorenz Bauer @ 2023-03-06 11:21 UTC (permalink / raw)
To: Martin KaFai Lau, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Song Liu, Yonghong Song, John Fastabend,
KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa
Cc: Lorenz Bauer, Martin KaFai Lau, bpf, linux-kernel
btf_datasec_resolve contains a bug that causes the following BTF
to fail loading:
[1] DATASEC a size=2 vlen=2
type_id=4 offset=0 size=1
type_id=7 offset=1 size=1
[2] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none)
[3] PTR (anon) type_id=2
[4] VAR a type_id=3 linkage=0
[5] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none)
[6] TYPEDEF td type_id=5
[7] VAR b type_id=6 linkage=0
This error message is printed during btf_check_all_types:
[1] DATASEC a size=2 vlen=2
type_id=7 offset=1 size=1 Invalid type
By tracing btf_*_resolve we can pinpoint the problem:
btf_datasec_resolve(depth: 1, type_id: 1, mode: RESOLVE_TBD) = 0
btf_var_resolve(depth: 2, type_id: 4, mode: RESOLVE_TBD) = 0
btf_ptr_resolve(depth: 3, type_id: 3, mode: RESOLVE_PTR) = 0
btf_var_resolve(depth: 2, type_id: 4, mode: RESOLVE_PTR) = 0
btf_datasec_resolve(depth: 1, type_id: 1, mode: RESOLVE_PTR) = -22
The last invocation of btf_datasec_resolve should invoke btf_var_resolve
by means of env_stack_push, instead it returns EINVAL. The reason is that
env_stack_push is never executed for the second VAR.
if (!env_type_is_resolve_sink(env, var_type) &&
!env_type_is_resolved(env, var_type_id)) {
env_stack_set_next_member(env, i + 1);
return env_stack_push(env, var_type, var_type_id);
}
env_type_is_resolve_sink() changes its behaviour based on resolve_mode.
For RESOLVE_PTR, we can simplify the if condition to the following:
(btf_type_is_modifier() || btf_type_is_ptr) && !env_type_is_resolved()
Since we're dealing with a VAR the clause evaluates to false. This is
not sufficient to trigger the bug however. The log output and EINVAL
are only generated if btf_type_id_size() fails.
if (!btf_type_id_size(btf, &type_id, &type_size)) {
btf_verifier_log_vsi(env, v->t, vsi, "Invalid type");
return -EINVAL;
}
Most types are sized, so for example a VAR referring to an INT is not a
problem. The bug is only triggered if a VAR points at a modifier. Since
we skipped btf_var_resolve that modifier was also never resolved, which
means that btf_resolved_type_id returns 0 aka VOID for the modifier.
This in turn causes btf_type_id_size to return NULL, triggering EINVAL.
To summarise, the following conditions are necessary:
- VAR pointing at PTR, STRUCT, UNION or ARRAY
- Followed by a VAR pointing at TYPEDEF, VOLATILE, CONST, RESTRICT or
TYPE_TAG
The fix is to reset resolve_mode to RESOLVE_TBD before attempting to
resolve a VAR from a DATASEC.
Fixes: 1dc92851849c ("bpf: kernel side support for BTF Var and DataSec")
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
---
kernel/bpf/btf.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index fa22ec79ac0e..73780748404c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4569,6 +4569,7 @@ static int btf_datasec_resolve(struct btf_verifier_env *env,
struct btf *btf = env->btf;
u16 i;
+ env->resolve_mode = RESOLVE_TBD;
for_each_vsi_from(i, v->next_member, v->t, vsi) {
u32 var_type_id = vsi->type, type_id, type_size = 0;
const struct btf_type *var_type = btf_type_by_id(env->btf,
--
2.39.2
^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH bpf v2 2/2] selftests/bpf: check that modifier resolves after pointer
[not found] <20230306112138.155352-1-lmb@isovalent.com>
2023-03-06 11:21 ` [PATCH bpf v2 1/2] btf: fix resolving BTF_KIND_VAR after ARRAY, STRUCT, UNION, PTR Lorenz Bauer
@ 2023-03-06 11:21 ` Lorenz Bauer
1 sibling, 0 replies; 3+ messages in thread
From: Lorenz Bauer @ 2023-03-06 11:21 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend,
KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa, Mykola Lysenko,
Shuah Khan
Cc: Lorenz Bauer, bpf, linux-kselftest, linux-kernel
Add a regression test that ensures that a VAR pointing at a
modifier which follows a PTR (or STRUCT or ARRAY) is resolved
correctly by the datasec validator.
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
---
tools/testing/selftests/bpf/prog_tests/btf.c | 28 ++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c
index cbb600be943d..210d643fda6c 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf.c
@@ -879,6 +879,34 @@ static struct btf_raw_test raw_tests[] = {
.btf_load_err = true,
.err_str = "Invalid elem",
},
+{
+ .descr = "var after datasec, ptr followed by modifier",
+ .raw_types = {
+ /* .bss section */ /* [1] */
+ BTF_TYPE_ENC(NAME_TBD, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 2),
+ sizeof(void*)+4),
+ BTF_VAR_SECINFO_ENC(4, 0, sizeof(void*)),
+ BTF_VAR_SECINFO_ENC(6, sizeof(void*), 4),
+ /* int */ /* [2] */
+ BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),
+ /* int* */ /* [3] */
+ BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_PTR, 0, 0), 2),
+ BTF_VAR_ENC(NAME_TBD, 3, 0), /* [4] */
+ /* const int */ /* [5] */
+ BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_CONST, 0, 0), 2),
+ BTF_VAR_ENC(NAME_TBD, 5, 0), /* [6] */
+ BTF_END_RAW,
+ },
+ .str_sec = "\0a\0b\0c\0",
+ .str_sec_size = sizeof("\0a\0b\0c\0"),
+ .map_type = BPF_MAP_TYPE_ARRAY,
+ .map_name = ".bss",
+ .key_size = sizeof(int),
+ .value_size = sizeof(void*)+4,
+ .key_type_id = 0,
+ .value_type_id = 1,
+ .max_entries = 1,
+},
/* Test member exceeds the size of struct.
*
* struct A {
--
2.39.2
^ permalink raw reply [flat|nested] 3+ messages in thread