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bpf: Support for new btf kind BTF_KIND_TAG

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LLVM14 added support for a new C attribute ([1])
  __attribute__((btf_tag("arbitrary_str")))
This attribute will be emitted to dwarf ([2]) and pahole
will convert it to BTF. Or for bpf target, this
attribute will be emitted to BTF directly ([3], [4]).
The attribute is intended to provide additional
information for
  - struct/union type or struct/union member
  - static/global variables
  - static/global function or function parameter.

For linux kernel, the btf_tag can be applied
in various places to specify user pointer,
function pre- or post- condition, function
allow/deny in certain context, etc. Such information
will be encoded in vmlinux BTF and can be used
by verifier.

The btf_tag can also be applied to bpf programs
to help global verifiable functions, e.g.,
specifying preconditions, etc.

This patch added basic parsing and checking support
in kernel for new BTF_KIND_TAG kind.

 [1] https://reviews.llvm.org/D106614
 [2] https://reviews.llvm.org/D106621
 [3] https://reviews.llvm.org/D106622
 [4] https://reviews.llvm.org/D109560

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210914223015.245546-1-yhs@fb.com
This commit is contained in:
Yonghong Song 2021-09-14 15:30:15 -07:00 committed by Alexei Starovoitov
parent 41ced4cd88
commit b5ea834dde
3 changed files with 154 additions and 2 deletions
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14
include/uapi/linux/btf.h
View File

@ -43,7 +43,7 @@ struct btf_type {
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
* FUNC, FUNC_PROTO and VAR.
* FUNC, FUNC_PROTO, VAR and TAG.
* "type" is a type_id referring to another type.
*/
union {
@ -74,6 +74,7 @@ enum {
BTF_KIND_VAR = 14, /* Variable */
BTF_KIND_DATASEC = 15, /* Section */
BTF_KIND_FLOAT = 16, /* Floating point */
BTF_KIND_TAG = 17, /* Tag */
NR_BTF_KINDS,
BTF_KIND_MAX = NR_BTF_KINDS - 1,
@ -173,4 +174,15 @@ struct btf_var_secinfo {
__u32 size;
};
/* BTF_KIND_TAG is followed by a single "struct btf_tag" to describe
* additional information related to the tag applied location.
* If component_idx == -1, the tag is applied to a struct, union,
* variable or function. Otherwise, it is applied to a struct/union
* member or a func argument, and component_idx indicates which member
* or argument (0 ... vlen-1).
*/
struct btf_tag {
__s32 component_idx;
};
#endif /* _UAPI__LINUX_BTF_H__ */

128
kernel/bpf/btf.c
View File

@ -281,6 +281,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_VAR] = "VAR",
[BTF_KIND_DATASEC] = "DATASEC",
[BTF_KIND_FLOAT] = "FLOAT",
[BTF_KIND_TAG] = "TAG",
};
const char *btf_type_str(const struct btf_type *t)
@ -459,6 +460,17 @@ static bool btf_type_is_datasec(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
}
static bool btf_type_is_tag(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info) == BTF_KIND_TAG;
}
static bool btf_type_is_tag_target(const struct btf_type *t)
{
return btf_type_is_func(t) || btf_type_is_struct(t) ||
btf_type_is_var(t);
}
u32 btf_nr_types(const struct btf *btf)
{
u32 total = 0;
@ -537,6 +549,7 @@ const struct btf_type *btf_type_resolve_func_ptr(const struct btf *btf,
static bool btf_type_is_resolve_source_only(const struct btf_type *t)
{
return btf_type_is_var(t) ||
btf_type_is_tag(t) ||
btf_type_is_datasec(t);
}
@ -563,6 +576,7 @@ static bool btf_type_needs_resolve(const struct btf_type *t)
btf_type_is_struct(t) ||
btf_type_is_array(t) ||
btf_type_is_var(t) ||
btf_type_is_tag(t) ||
btf_type_is_datasec(t);
}
@ -616,6 +630,11 @@ static const struct btf_var *btf_type_var(const struct btf_type *t)
return (const struct btf_var *)(t + 1);
}
static const struct btf_tag *btf_type_tag(const struct btf_type *t)
{
return (const struct btf_tag *)(t + 1);
}
static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
{
return kind_ops[BTF_INFO_KIND(t->info)];
@ -3801,6 +3820,110 @@ static const struct btf_kind_operations float_ops = {
.show = btf_df_show,
};
static s32 btf_tag_check_meta(struct btf_verifier_env *env,
const struct btf_type *t,
u32 meta_left)
{
const struct btf_tag *tag;
u32 meta_needed = sizeof(*tag);
s32 component_idx;
const char *value;
if (meta_left < meta_needed) {
btf_verifier_log_basic(env, t,
"meta_left:%u meta_needed:%u",
meta_left, meta_needed);
return -EINVAL;
}
value = btf_name_by_offset(env->btf, t->name_off);
if (!value || !value[0]) {
btf_verifier_log_type(env, t, "Invalid value");
return -EINVAL;
}
if (btf_type_vlen(t)) {
btf_verifier_log_type(env, t, "vlen != 0");
return -EINVAL;
}
if (btf_type_kflag(t)) {
btf_verifier_log_type(env, t, "Invalid btf_info kind_flag");
return -EINVAL;
}
component_idx = btf_type_tag(t)->component_idx;
if (component_idx < -1) {
btf_verifier_log_type(env, t, "Invalid component_idx");
return -EINVAL;
}
btf_verifier_log_type(env, t, NULL);
return meta_needed;
}
static int btf_tag_resolve(struct btf_verifier_env *env,
const struct resolve_vertex *v)
{
const struct btf_type *next_type;
const struct btf_type *t = v->t;
u32 next_type_id = t->type;
struct btf *btf = env->btf;
s32 component_idx;
u32 vlen;
next_type = btf_type_by_id(btf, next_type_id);
if (!next_type || !btf_type_is_tag_target(next_type)) {
btf_verifier_log_type(env, v->t, "Invalid type_id");
return -EINVAL;
}
if (!env_type_is_resolve_sink(env, next_type) &&
!env_type_is_resolved(env, next_type_id))
return env_stack_push(env, next_type, next_type_id);
component_idx = btf_type_tag(t)->component_idx;
if (component_idx != -1) {
if (btf_type_is_var(next_type)) {
btf_verifier_log_type(env, v->t, "Invalid component_idx");
return -EINVAL;
}
if (btf_type_is_struct(next_type)) {
vlen = btf_type_vlen(next_type);
} else {
/* next_type should be a function */
next_type = btf_type_by_id(btf, next_type->type);
vlen = btf_type_vlen(next_type);
}
if ((u32)component_idx >= vlen) {
btf_verifier_log_type(env, v->t, "Invalid component_idx");
return -EINVAL;
}
}
env_stack_pop_resolved(env, next_type_id, 0);
return 0;
}
static void btf_tag_log(struct btf_verifier_env *env, const struct btf_type *t)
{
btf_verifier_log(env, "type=%u component_idx=%d", t->type,
btf_type_tag(t)->component_idx);
}
static const struct btf_kind_operations tag_ops = {
.check_meta = btf_tag_check_meta,
.resolve = btf_tag_resolve,
.check_member = btf_df_check_member,
.check_kflag_member = btf_df_check_kflag_member,
.log_details = btf_tag_log,
.show = btf_df_show,
};
static int btf_func_proto_check(struct btf_verifier_env *env,
const struct btf_type *t)
{
@ -3935,6 +4058,7 @@ static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS] = {
[BTF_KIND_VAR] = &var_ops,
[BTF_KIND_DATASEC] = &datasec_ops,
[BTF_KIND_FLOAT] = &float_ops,
[BTF_KIND_TAG] = &tag_ops,
};
static s32 btf_check_meta(struct btf_verifier_env *env,
@ -4019,6 +4143,10 @@ static bool btf_resolve_valid(struct btf_verifier_env *env,
return !btf_resolved_type_id(btf, type_id) &&
!btf_resolved_type_size(btf, type_id);
if (btf_type_is_tag(t))
return btf_resolved_type_id(btf, type_id) &&
!btf_resolved_type_size(btf, type_id);
if (btf_type_is_modifier(t) || btf_type_is_ptr(t) ||
btf_type_is_var(t)) {
t = btf_type_id_resolve(btf, &type_id);

14
tools/include/uapi/linux/btf.h
View File

@ -43,7 +43,7 @@ struct btf_type {
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
* FUNC, FUNC_PROTO and VAR.
* FUNC, FUNC_PROTO, VAR and TAG.
* "type" is a type_id referring to another type.
*/
union {
@ -74,6 +74,7 @@ enum {
BTF_KIND_VAR = 14, /* Variable */
BTF_KIND_DATASEC = 15, /* Section */
BTF_KIND_FLOAT = 16, /* Floating point */
BTF_KIND_TAG = 17, /* Tag */
NR_BTF_KINDS,
BTF_KIND_MAX = NR_BTF_KINDS - 1,
@ -173,4 +174,15 @@ struct btf_var_secinfo {
__u32 size;
};
/* BTF_KIND_TAG is followed by a single "struct btf_tag" to describe
* additional information related to the tag applied location.
* If component_idx == -1, the tag is applied to a struct, union,
* variable or function. Otherwise, it is applied to a struct/union
* member or a func argument, and component_idx indicates which member
* or argument (0 ... vlen-1).
*/
struct btf_tag {
__s32 component_idx;
};
#endif /* _UAPI__LINUX_BTF_H__ */