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bpf: Support BTF_KIND_TYPE_TAG for btf_type_tag attributes 

LLVM patches ([1] for clang, [2] and [3] for BPF backend)
added support for btf_type_tag attributes. This patch
added support for the kernel.

The main motivation for btf_type_tag is to bring kernel
annotations __user, __rcu etc. to btf. With such information
available in btf, bpf verifier can detect mis-usages
and reject the program. For example, for __user tagged pointer,
developers can then use proper helper like bpf_probe_read_user()
etc. to read the data.

BTF_KIND_TYPE_TAG may also useful for other tracing
facility where instead of to require user to specify
kernel/user address type, the kernel can detect it
by itself with btf.

  [1] https://reviews.llvm.org/D111199
  [2] https://reviews.llvm.org/D113222
  [3] https://reviews.llvm.org/D113496

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/20211112012609.1505032-1-yhs@fb.com
This commit is contained in:
Yonghong Song 2021-11-11 17:26:09 -08:00 committed by Alexei Starovoitov
parent 2326ff8d5c
commit 8c42d2fa4e
3 changed files with 17 additions and 3 deletions
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3
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, VAR and DECL_TAG.
* FUNC, FUNC_PROTO, VAR, DECL_TAG and TYPE_TAG.
* "type" is a type_id referring to another type.
*/
union {
@ -75,6 +75,7 @@ enum {
BTF_KIND_DATASEC = 15, /* Section */
BTF_KIND_FLOAT = 16, /* Floating point */
BTF_KIND_DECL_TAG = 17, /* Decl Tag */
BTF_KIND_TYPE_TAG = 18, /* Type Tag */
NR_BTF_KINDS,
BTF_KIND_MAX = NR_BTF_KINDS - 1,

14
kernel/bpf/btf.c
View File

@ -282,6 +282,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_DATASEC] = "DATASEC",
[BTF_KIND_FLOAT] = "FLOAT",
[BTF_KIND_DECL_TAG] = "DECL_TAG",
[BTF_KIND_TYPE_TAG] = "TYPE_TAG",
};
const char *btf_type_str(const struct btf_type *t)
@ -418,6 +419,7 @@ static bool btf_type_is_modifier(const struct btf_type *t)
case BTF_KIND_VOLATILE:
case BTF_KIND_CONST:
case BTF_KIND_RESTRICT:
case BTF_KIND_TYPE_TAG:
return true;
}
@ -1737,6 +1739,7 @@ __btf_resolve_size(const struct btf *btf, const struct btf_type *type,
case BTF_KIND_VOLATILE:
case BTF_KIND_CONST:
case BTF_KIND_RESTRICT:
case BTF_KIND_TYPE_TAG:
id = type->type;
type = btf_type_by_id(btf, type->type);
break;
@ -2345,6 +2348,8 @@ static int btf_ref_type_check_meta(struct btf_verifier_env *env,
const struct btf_type *t,
u32 meta_left)
{
const char *value;
if (btf_type_vlen(t)) {
btf_verifier_log_type(env, t, "vlen != 0");
return -EINVAL;
@ -2360,7 +2365,7 @@ static int btf_ref_type_check_meta(struct btf_verifier_env *env,
return -EINVAL;
}
/* typedef type must have a valid name, and other ref types,
/* typedef/type_tag type must have a valid name, and other ref types,
* volatile, const, restrict, should have a null name.
*/
if (BTF_INFO_KIND(t->info) == BTF_KIND_TYPEDEF) {
@ -2369,6 +2374,12 @@ static int btf_ref_type_check_meta(struct btf_verifier_env *env,
btf_verifier_log_type(env, t, "Invalid name");
return -EINVAL;
}
} else if (BTF_INFO_KIND(t->info) == BTF_KIND_TYPE_TAG) {
value = btf_name_by_offset(env->btf, t->name_off);
if (!value || !value[0]) {
btf_verifier_log_type(env, t, "Invalid name");
return -EINVAL;
}
} else {
if (t->name_off) {
btf_verifier_log_type(env, t, "Invalid name");
@ -4059,6 +4070,7 @@ static const struct btf_kind_operations * const kind_ops[NR_BTF_KINDS] = {
[BTF_KIND_DATASEC] = &datasec_ops,
[BTF_KIND_FLOAT] = &float_ops,
[BTF_KIND_DECL_TAG] = &decl_tag_ops,
[BTF_KIND_TYPE_TAG] = &modifier_ops,
};
static s32 btf_check_meta(struct btf_verifier_env *env,

3
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, VAR and DECL_TAG.
* FUNC, FUNC_PROTO, VAR, DECL_TAG and TYPE_TAG.
* "type" is a type_id referring to another type.
*/
union {
@ -75,6 +75,7 @@ enum {
BTF_KIND_DATASEC = 15, /* Section */
BTF_KIND_FLOAT = 16, /* Floating point */
BTF_KIND_DECL_TAG = 17, /* Decl Tag */
BTF_KIND_TYPE_TAG = 18, /* Type Tag */
NR_BTF_KINDS,
BTF_KIND_MAX = NR_BTF_KINDS - 1,