[RFC PATCH v6 7/7] btf: Add sorting validation for binary search

[Donglin Peng <dolinux.peng@gmail.com>]

From: Donglin Peng <pengdonglin@xiaomi.com>

Implement validation of BTF type ordering to enable efficient binary
search for sorted BTF.

Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Song Liu <song@kernel.org>
Cc: Xiaoqin Zhang <zhangxiaoqin@xiaomi.com>
Signed-off-by: Donglin Peng <pengdonglin@xiaomi.com>
---
 kernel/bpf/btf.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 5dd2c40d4874..e9d102360292 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -550,6 +550,66 @@ u32 btf_nr_types(const struct btf *btf)
 	return total;
 }
 
+/* Anonymous types (with empty names) are considered greater than named types
+ * and are sorted after them. Two anonymous types are considered equal. Named
+ * types are compared lexicographically.
+ */
+static int btf_compare_type_names(const void *a, const void *b, void *priv)
+{
+	struct btf *btf = (struct btf *)priv;
+	const struct btf_type *ta = btf_type_by_id(btf, *(__u32 *)a);
+	const struct btf_type *tb = btf_type_by_id(btf, *(__u32 *)b);
+	const char *na, *nb;
+
+	if (!ta->name_off && tb->name_off)
+		return 1;
+	if (ta->name_off && !tb->name_off)
+		return -1;
+	if (!ta->name_off && !tb->name_off)
+		return 0;
+
+	na = btf_name_by_offset(btf, ta->name_off);
+	nb = btf_name_by_offset(btf, tb->name_off);
+	return strcmp(na, nb);
+}
+
+/* Verifies that BTF types are sorted in ascending order according to their
+ * names, with named types appearing before anonymous types. If the ordering
+ * is correct, counts the number of named types and updates the BTF object's
+ * nr_sorted_types field. Note that vmlinux and kernel module BTFs are sorted
+ * during the building phase, so the validation logic only needs to count the
+ * named types.
+ */
+static void btf_check_sorted(struct btf *btf)
+{
+	const struct btf_type *t;
+	int i, n, k = 0, nr_sorted_types;
+	bool skip_cmp = btf_is_kernel(btf);
+
+	if (btf->nr_types < 2)
+		return;
+
+	nr_sorted_types = 0;
+	n = btf_nr_types(btf) - 1;
+	for (i = btf_start_id(btf); i < n; i++) {
+		k = i + 1;
+		if (!skip_cmp && btf_compare_type_names(&i, &k, btf) > 0)
+			return;
+
+		t = btf_type_by_id(btf, i);
+		if (t->name_off)
+			nr_sorted_types++;
+		else if (skip_cmp)
+			break;
+	}
+
+	t = btf_type_by_id(btf, k);
+	if (t->name_off)
+		nr_sorted_types++;
+	if (nr_sorted_types)
+		btf->nr_sorted_types = nr_sorted_types;
+}
+
 static s32 btf_find_by_name_kind_bsearch(const struct btf *btf, const char *name,
 						s32 start_id, s32 end_id)
 {
@@ -5885,6 +5945,8 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat
 	if (err)
 		goto errout;
 
+	btf_check_sorted(btf);
+
 	struct_meta_tab = btf_parse_struct_metas(&env->log, btf);
 	if (IS_ERR(struct_meta_tab)) {
 		err = PTR_ERR(struct_meta_tab);
@@ -6292,6 +6354,7 @@ static struct btf *btf_parse_base(struct btf_verifier_env *env, const char *name
 	if (err)
 		goto errout;
 
+	btf_check_sorted(btf);
 	refcount_set(&btf->refcnt, 1);
 
 	return btf;
@@ -6426,6 +6489,7 @@ static struct btf *btf_parse_module(const char *module_name, const void *data,
 	}
 
 	btf_verifier_env_free(env);
+	btf_check_sorted(btf);
 	refcount_set(&btf->refcnt, 1);
 	return btf;
 
-- 
2.34.1