[PATCH v6 bpf-next 06/10] btf: support kernel parsing of BTF with kind layout

Alan Maguire
2025-12-10T20:33:36Z

Validate kind layout if present, but because the kernel must be
strict in what it accepts, reject BTF with unsupported kinds,
even if they are in the kind layout information.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
kernel/bpf/btf.c | 96 ++++++++++++++++++++++++++++++++++++++----------
1 file changed, 76 insertions(+), 20 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0de8fc8a0e0b..eb4ac78b453a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -268,6 +268,7 @@ struct btf {
struct btf_id_dtor_kfunc_tab *dtor_kfunc_tab;
struct btf_struct_metas *struct_meta_tab;
struct btf_struct_ops_tab *struct_ops_tab;
+ struct btf_kind_layout *kind_layout;

/* split BTF support */
struct btf *base_btf;
@@ -5215,23 +5216,36 @@ static s32 btf_check_meta(struct btf_verifier_env *env,
return -EINVAL;
}

- if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX ||
- BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
+ if (!btf_name_offset_valid(env->btf, t->name_off)) {
+ btf_verifier_log(env, "[%u] Invalid name_offset:%u",
+ env->log_type_id, t->name_off);
+ return -EINVAL;
+ }
+
+ if (BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
btf_verifier_log(env, "[%u] Invalid kind:%u",
env->log_type_id, BTF_INFO_KIND(t->info));
return -EINVAL;
}

- if (!btf_name_offset_valid(env->btf, t->name_off)) {
- btf_verifier_log(env, "[%u] Invalid name_offset:%u",
- env->log_type_id, t->name_off);
+ if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX && env->btf->kind_layout &&
+ (BTF_INFO_KIND(t->info) * sizeof(struct btf_kind_layout)) <
+ env->btf->hdr.kind_layout_len) {
+ btf_verifier_log(env, "[%u] unknown but required kind %u",
+ env->log_type_id,
+ BTF_INFO_KIND(t->info));
return -EINVAL;
+ } else {
+ if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX) {
+ btf_verifier_log(env, "[%u] Invalid kind:%u",
+ env->log_type_id, BTF_INFO_KIND(t->info));
+ return -EINVAL;
+ }
+ var_meta_size = btf_type_ops(t)->check_meta(env, t, meta_left);
+ if (var_meta_size < 0)
+ return var_meta_size;
}

- var_meta_size = btf_type_ops(t)->check_meta(env, t, meta_left);
- if (var_meta_size < 0)
- return var_meta_size;
-
meta_left -= var_meta_size;

return saved_meta_left - meta_left;
@@ -5405,7 +5419,8 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
start = btf->nohdr_data + hdr->str_off;
end = start + hdr->str_len;

- if (end != btf->data + btf->data_size) {
+ if (hdr->hdr_len < sizeof(struct btf_header) &&
+ end != btf->data + btf->data_size) {
btf_verifier_log(env, "String section is not at the end");
return -EINVAL;
}
@@ -5426,9 +5441,41 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
return 0;
}

+static int btf_parse_kind_layout_sec(struct btf_verifier_env *env)
+{
+ const struct btf_header *hdr = &env->btf->hdr;
+ struct btf *btf = env->btf;
+ void *start, *end;
+
+ if (hdr->hdr_len < sizeof(struct btf_header) ||
+ hdr->kind_layout_len == 0)
+ return 0;
+
+ /* Kind layout section must align to 4 bytes */
+ if (hdr->kind_layout_off & (sizeof(u32) - 1)) {
+ btf_verifier_log(env, "Unaligned kind_layout_off");
+ return -EINVAL;
+ }
+ start = btf->nohdr_data + hdr->kind_layout_off;
+ end = start + hdr->kind_layout_len;
+
+ if (hdr->kind_layout_len < sizeof(struct btf_kind_layout)) {
+ btf_verifier_log(env, "Kind layout section is too small");
+ return -EINVAL;
+ }
+ if (end != btf->data + btf->data_size) {
+ btf_verifier_log(env, "Kind layout section is not at the end");
+ return -EINVAL;
+ }
+ btf->kind_layout = start;
+
+ return 0;
+}
+
static const size_t btf_sec_info_offset[] = {
offsetof(struct btf_header, type_off),
offsetof(struct btf_header, str_off),
+ offsetof(struct btf_header, kind_layout_off),
};

static int btf_sec_info_cmp(const void *a, const void *b)
@@ -5443,44 +5490,49 @@ static int btf_check_sec_info(struct btf_verifier_env *env,
u32 btf_data_size)
{
struct btf_sec_info secs[ARRAY_SIZE(btf_sec_info_offset)];
- u32 total, expected_total, i;
+ u32 nr_secs = ARRAY_SIZE(btf_sec_info_offset);
+ u32 total, expected_total, gap, i;
const struct btf_header *hdr;
const struct btf *btf;

btf = env->btf;
hdr = &btf->hdr;

+ if (hdr->hdr_len < sizeof(struct btf_header))
+ nr_secs--;
+
/* Populate the secs from hdr */
- for (i = 0; i < ARRAY_SIZE(btf_sec_info_offset); i++)
+ for (i = 0; i < nr_secs; i++)
secs[i] = *(struct btf_sec_info *)((void *)hdr +
btf_sec_info_offset[i]);

- sort(secs, ARRAY_SIZE(btf_sec_info_offset),
+ sort(secs, nr_secs,
sizeof(struct btf_sec_info), btf_sec_info_cmp, NULL);

/* Check for gaps and overlap among sections */
total = 0;
expected_total = btf_data_size - hdr->hdr_len;
- for (i = 0; i < ARRAY_SIZE(btf_sec_info_offset); i++) {
+ for (i = 0; i < nr_secs; i++) {
if (expected_total < secs[i].off) {
btf_verifier_log(env, "Invalid section offset");
return -EINVAL;
}
- if (total < secs[i].off) {
- /* gap */
- btf_verifier_log(env, "Unsupported section found");
- return -EINVAL;
- }
if (total > secs[i].off) {
btf_verifier_log(env, "Section overlap found");
return -EINVAL;
}
+ gap = secs[i].off - total;
+ if (gap >= 4) {
+ /* gap larger than alignment gap */
+ btf_verifier_log(env, "Unsupported section found");
+ return -EINVAL;
+ }
if (expected_total - total < secs[i].len) {
btf_verifier_log(env,
"Total section length too long");
return -EINVAL;
}
- total += secs[i].len;
+ total += secs[i].len + gap;
}

/* There is data other than hdr and known sections */
@@ -5816,6 +5868,10 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat
if (err)
goto errout;

+ err = btf_parse_kind_layout_sec(env);
+ if (err)
+ goto errout;
+
err = btf_parse_type_sec(env);
if (err)
goto errout;
--
2.43.5