Add feature check for kernel extended vlen/kind support, and reject
BTF that uses extended vlens/kinds if the kernel does not support
it.  There is no reasonable path to generally sanitize such BTF.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/features.c        | 39 +++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.c          | 17 +++++++++++++-
 tools/lib/bpf/libbpf_internal.h |  2 ++
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index 4f19a0d79b0c..4a75d6717bbb 100644
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -615,6 +615,42 @@ static int probe_kern_btf_layout(int token_fd)
 						 (char *)layout, token_fd));
 }
 
+static int probe_kern_btf_vlen_kind_extended(int token_fd)
+{
+	struct btf *btf;
+	int ret = 0;
+	__s32 id;
+	int err;
+
+	btf = btf__load_vmlinux_btf();
+	err = libbpf_get_error(btf);
+	if (err)
+		return err;
+	id = btf__find_by_name_kind(btf, "btf_max", BTF_KIND_ENUM);
+	if (id > 0) {
+		const struct btf_type *t;
+		const struct btf_enum *e;
+		const char *name;
+		__u32 i, vlen;
+
+		t = btf__type_by_id(btf, id);
+		if (t) {
+			vlen = btf_vlen(t);
+
+			for (i = 0, e = btf_enum(t); i < vlen; i++, e++) {
+				name = btf__name_by_offset(btf, e->name_off);
+				if (!name || strcmp(name, "BTF_MAX_VLEN") != 0)
+					continue;
+				if (e->val > 0xffff)
+					ret = 1;
+			}
+		}
+	}
+	btf__free(btf);
+
+	return ret;
+}
+
 typedef int (*feature_probe_fn)(int /* token_fd */);
 
 static struct kern_feature_cache feature_cache;
@@ -699,6 +735,9 @@ static struct kern_feature_desc {
 	[FEAT_BTF_LAYOUT] = {
 		"kernel supports BTF layout", probe_kern_btf_layout,
 	},
+	[FEAT_BTF_VLEN_KIND_EXTENDED] = {
+		"kernel supports extended BTF vlen/kind", probe_kern_btf_vlen_kind_extended,
+	},
 };
 
 bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8b0c3246097f..5f19d8ac17a9 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3139,10 +3139,11 @@ static bool btf_needs_sanitization(struct bpf_object *obj)
 	bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);
 	bool has_qmark_datasec = kernel_supports(obj, FEAT_BTF_QMARK_DATASEC);
 	bool has_layout = kernel_supports(obj, FEAT_BTF_LAYOUT);
+	bool has_vlen_kind_extended = kernel_supports(obj, FEAT_BTF_VLEN_KIND_EXTENDED);
 
 	return !has_func || !has_datasec || !has_func_global || !has_float ||
 	       !has_decl_tag || !has_type_tag || !has_enum64 || !has_qmark_datasec ||
-	       !has_layout;
+	       !has_layout || !has_vlen_kind_extended;
 }
 
 struct btf *bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *orig_btf)
@@ -3156,6 +3157,7 @@ struct btf *bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *orig_bt
 	bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);
 	bool has_qmark_datasec = kernel_supports(obj, FEAT_BTF_QMARK_DATASEC);
 	bool has_layout = kernel_supports(obj, FEAT_BTF_LAYOUT);
+	bool has_vlen_kind_extended = kernel_supports(obj, FEAT_BTF_VLEN_KIND_EXTENDED);
 	int enum64_placeholder_id = 0;
 	const struct btf_header *hdr;
 	struct btf *btf = NULL;
@@ -3217,6 +3219,19 @@ struct btf *bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *orig_bt
 	for (i = 1; i < btf__type_cnt(btf); i++) {
 		t = (struct btf_type *)btf__type_by_id(btf, i);
 
+		/*
+		 * If BTF uses extended vlen/kind and kernel does not support
+		 * it, there is nothing we can do.
+		 */
+		if (!has_vlen_kind_extended) {
+			if (btf_vlen(t) > 0xffff || btf_kind(t) > 0x1f) {
+				pr_debug("Unsupported %s for id %u\n",
+					 btf_kind(t) > 0x1f ? "BTF kind" : "BTF vlen", i);
+				btf__free(btf);
+				return ERR_PTR(-EINVAL);
+			}
+		}
+
 		if ((!has_datasec && btf_is_var(t)) || (!has_decl_tag && btf_is_decl_tag(t))) {
 			/* replace VAR/DECL_TAG with INT */
 			t->info = BTF_INFO_ENC(BTF_KIND_INT, 0, 0);
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 3781c45b46d3..8ef1fc96b73a 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -398,6 +398,8 @@ enum kern_feature_id {
 	FEAT_UPROBE_SYSCALL,
 	/* Kernel supports BTF layout information */
 	FEAT_BTF_LAYOUT,
+	/* Kernel supports BTF vlen > 65535 */
+	FEAT_BTF_VLEN_KIND_EXTENDED,
 	__FEAT_CNT,
 };
 
-- 
2.39.3