bpf: Extend BTF UAPI vlen, kinds to use unused bits

BTF maximum vlen is encoded using 16 bits with a maximum vlen
of 65535.  This has sufficed for structs, function parameters
and enumerated type values.  However, with upcoming BTF location
information - in particular information about inline sites -
this limit is surpassed.  Use bits 16-23 - currently unused in
BTF info - to extend to 24 bits, giving a max vlen of (2^24 - 1),
or 16 million.

Also extend BTF kind encoding from 5 to 7 bits, giving a maximum
available number of kinds of 128.  Since with the BTF location work
we use another 3 kinds, we are fast approaching the current limit
of 32.

Convert BTF_MAX_* values to enums to allow them to be encoded in
kernel BTF; this will allow us to detect if the running kernel
supports a 24-bit vlen or not.  Add one for max _possible_
(not used) kind.

Fix up a few places in the kernel where a 16-bit vlen is assumed;
remove BTF_INFO_MASK as now all bits are used.

The vlen expansion was suggested by Andrii in [1]; the kind expansion
is tackled here too as it may be needed also to support new kinds
in BTF.

[1] https://lore.kernel.org/bpf/CAEf4BzZx=X6vGqcA8SPU6D+v6k+TR=ZewebXMuXtpmML058piw@mail.gmail.com/

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Link: https://lore.kernel.org/r/20260417143023.1551481-2-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 40 insertions, 43 deletions

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 48108471c5b1..c82d0d689059 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -415,12 +415,12 @@ static inline bool btf_type_is_array(const struct btf_type *t)
 	return BTF_INFO_KIND(t->info) == BTF_KIND_ARRAY;
 }
 
-static inline u16 btf_type_vlen(const struct btf_type *t)
+static inline u32 btf_type_vlen(const struct btf_type *t)
 {
 	return BTF_INFO_VLEN(t->info);
 }
 
-static inline u16 btf_vlen(const struct btf_type *t)
+static inline u32 btf_vlen(const struct btf_type *t)
 {
 	return btf_type_vlen(t);
 }
diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
index 638615ebddc2..618167cab4e6 100644
--- a/include/uapi/linux/btf.h
+++ b/include/uapi/linux/btf.h
@@ -33,20 +33,22 @@ struct btf_header {
 	__u32	layout_len;	/* length of layout section	*/
 };
 
-/* Max # of type identifier */
-#define BTF_MAX_TYPE	0x000fffff
-/* Max offset into the string section */
-#define BTF_MAX_NAME_OFFSET	0x00ffffff
-/* Max # of struct/union/enum members or func args */
-#define BTF_MAX_VLEN	0xffff
+enum btf_max {
+	/* Max possible kind */
+	BTF_MAX_KIND =		0x0000007f,
+	/* Max # of type identifier */
+	BTF_MAX_TYPE =		0x000fffff,
+	/* Max offset into the string section */
+	BTF_MAX_NAME_OFFSET =	0x00ffffff,
+	/* Max # of struct/union/enum members or func args */
+	BTF_MAX_VLEN =		0x00ffffff,
+};
 
 struct btf_type {
 	__u32 name_off;
 	/* "info" bits arrangement
-	 * bits  0-15: vlen (e.g. # of struct's members)
-	 * bits 16-23: unused
-	 * bits 24-28: kind (e.g. int, ptr, array...etc)
-	 * bits 29-30: unused
+	 * bits  0-23: vlen (e.g. # of struct's members)
+	 * bits 24-30: kind (e.g. int, ptr, array...etc)
 	 * bit     31: kind_flag, currently used by
 	 *             struct, union, enum, fwd, enum64,
 	 *             decl_tag and type_tag
@@ -65,8 +67,8 @@ struct btf_type {
 	};
 };
 
-#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x1f)
-#define BTF_INFO_VLEN(info)	((info) & 0xffff)
+#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x7f)
+#define BTF_INFO_VLEN(info)	((info) & 0xffffff)
 #define BTF_INFO_KFLAG(info)	((info) >> 31)
 
 enum {
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 3c2aaa3c5004..77af44d8a3ad 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -182,7 +182,6 @@
 #define BITS_ROUNDUP_BYTES(bits) \
 	(BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
 
-#define BTF_INFO_MASK 0x9f00ffff
 #define BTF_INT_MASK 0x0fffffff
 #define BTF_TYPE_ID_VALID(type_id) ((type_id) <= BTF_MAX_TYPE)
 #define BTF_STR_OFFSET_VALID(name_off) ((name_off) <= BTF_MAX_NAME_OFFSET)
@@ -289,7 +288,7 @@ enum verifier_phase {
 struct resolve_vertex {
 	const struct btf_type *t;
 	u32 type_id;
-	u16 next_member;
+	u32 next_member;
 };
 
 enum visit_state {
@@ -2031,7 +2030,7 @@ static int env_stack_push(struct btf_verifier_env *env,
 }
 
 static void env_stack_set_next_member(struct btf_verifier_env *env,
-				      u16 next_member)
+				      u32 next_member)
 {
 	env->stack[env->top_stack - 1].next_member = next_member;
 }
@@ -3293,7 +3292,7 @@ static s32 btf_struct_check_meta(struct btf_verifier_env *env,
 	struct btf *btf = env->btf;
 	u32 struct_size = t->size;
 	u32 offset;
-	u16 i;
+	u32 i;
 
 	meta_needed = btf_type_vlen(t) * sizeof(*member);
 	if (meta_left < meta_needed) {
@@ -3369,7 +3368,7 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
 {
 	const struct btf_member *member;
 	int err;
-	u16 i;
+	u32 i;
 
 	/* Before continue resolving the next_member,
 	 * ensure the last member is indeed resolved to a
@@ -4447,7 +4446,7 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
 	const struct btf_enum *enums = btf_type_enum(t);
 	struct btf *btf = env->btf;
 	const char *fmt_str;
-	u16 i, nr_enums;
+	u32 i, nr_enums;
 	u32 meta_needed;
 
 	nr_enums = btf_type_vlen(t);
@@ -4555,7 +4554,7 @@ static s32 btf_enum64_check_meta(struct btf_verifier_env *env,
 	const struct btf_enum64 *enums = btf_type_enum64(t);
 	struct btf *btf = env->btf;
 	const char *fmt_str;
-	u16 i, nr_enums;
+	u32 i, nr_enums;
 	u32 meta_needed;
 
 	nr_enums = btf_type_vlen(t);
@@ -4683,7 +4682,7 @@ static void btf_func_proto_log(struct btf_verifier_env *env,
 			       const struct btf_type *t)
 {
 	const struct btf_param *args = (const struct btf_param *)(t + 1);
-	u16 nr_args = btf_type_vlen(t), i;
+	u32 nr_args = btf_type_vlen(t), i;
 
 	btf_verifier_log(env, "return=%u args=(", t->type);
 	if (!nr_args) {
@@ -4929,7 +4928,7 @@ static int btf_datasec_resolve(struct btf_verifier_env *env,
 {
 	const struct btf_var_secinfo *vsi;
 	struct btf *btf = env->btf;
-	u16 i;
+	u32 i;
 
 	env->resolve_mode = RESOLVE_TBD;
 	for_each_vsi_from(i, v->next_member, v->t, vsi) {
@@ -5183,7 +5182,7 @@ static int btf_func_proto_check(struct btf_verifier_env *env,
 	const struct btf_type *ret_type;
 	const struct btf_param *args;
 	const struct btf *btf;
-	u16 nr_args, i;
+	u32 nr_args, i;
 	int err;
 
 	btf = env->btf;
@@ -5278,7 +5277,7 @@ static int btf_func_check(struct btf_verifier_env *env,
 	const struct btf_type *proto_type;
 	const struct btf_param *args;
 	const struct btf *btf;
-	u16 nr_args, i;
+	u32 nr_args, i;
 
 	btf = env->btf;
 	proto_type = btf_type_by_id(btf, t->type);
@@ -5336,12 +5335,6 @@ static s32 btf_check_meta(struct btf_verifier_env *env,
 	}
 	meta_left -= sizeof(*t);
 
-	if (t->info & ~BTF_INFO_MASK) {
-		btf_verifier_log(env, "[%u] Invalid btf_info:%x",
-				 env->log_type_id, t->info);
-		return -EINVAL;
-	}
-
 	if (BTF_INFO_KIND(t->info) > BTF_KIND_MAX ||
 	    BTF_INFO_KIND(t->info) == BTF_KIND_UNKN) {
 		btf_verifier_log(env, "[%u] Invalid kind:%u",
diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
index 638615ebddc2..618167cab4e6 100644
--- a/tools/include/uapi/linux/btf.h
+++ b/tools/include/uapi/linux/btf.h
@@ -33,20 +33,22 @@ struct btf_header {
 	__u32	layout_len;	/* length of layout section	*/
 };
 
-/* Max # of type identifier */
-#define BTF_MAX_TYPE	0x000fffff
-/* Max offset into the string section */
-#define BTF_MAX_NAME_OFFSET	0x00ffffff
-/* Max # of struct/union/enum members or func args */
-#define BTF_MAX_VLEN	0xffff
+enum btf_max {
+	/* Max possible kind */
+	BTF_MAX_KIND =		0x0000007f,
+	/* Max # of type identifier */
+	BTF_MAX_TYPE =		0x000fffff,
+	/* Max offset into the string section */
+	BTF_MAX_NAME_OFFSET =	0x00ffffff,
+	/* Max # of struct/union/enum members or func args */
+	BTF_MAX_VLEN =		0x00ffffff,
+};
 
 struct btf_type {
 	__u32 name_off;
 	/* "info" bits arrangement
-	 * bits  0-15: vlen (e.g. # of struct's members)
-	 * bits 16-23: unused
-	 * bits 24-28: kind (e.g. int, ptr, array...etc)
-	 * bits 29-30: unused
+	 * bits  0-23: vlen (e.g. # of struct's members)
+	 * bits 24-30: kind (e.g. int, ptr, array...etc)
 	 * bit     31: kind_flag, currently used by
 	 *             struct, union, enum, fwd, enum64,
 	 *             decl_tag and type_tag
@@ -65,8 +67,8 @@ struct btf_type {
 	};
 };
 
-#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x1f)
-#define BTF_INFO_VLEN(info)	((info) & 0xffff)
+#define BTF_INFO_KIND(info)	(((info) >> 24) & 0x7f)
+#define BTF_INFO_VLEN(info)	((info) & 0xffffff)
 #define BTF_INFO_KFLAG(info)	((info) >> 31)
 
 enum {