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bpf: Support BTF_KIND_TYPE_TAG for btf_type_tag attributes

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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
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@@ -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,