From: Alan Maguire Date: Fri, 17 Apr 2026 14:30:18 +0000 (+0100) Subject: bpf: Extend BTF UAPI vlen, kinds to use unused bits X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f7a6b9eaff3e6693ba3b19c5812e28538049bbf2;p=thirdparty%2Fkernel%2Flinux.git 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 Signed-off-by: Alan Maguire Acked-by: Mykyta Yatsenko Link: https://lore.kernel.org/r/20260417143023.1551481-2-alan.maguire@oracle.com Signed-off-by: Alexei Starovoitov --- diff --git a/include/linux/btf.h b/include/linux/btf.h index 48108471c5b13..c82d0d6890591 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 638615ebddc22..618167cab4e61 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 3c2aaa3c50049..77af44d8a3ad3 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 638615ebddc22..618167cab4e61 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 {