libbpf: Add bpf object kern_version attribute setter

mainline inclusion
from mainline-5.13-rc1
commit 155f556d
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=155f556d64b1a48710f01305e14bb860734ed1e3

-------------------------------------------------

Unfortunately some distros don't have their kernel version defined
accurately in <linux/version.h> due to different long term support
reasons.

It is important to have a way to override the bpf kern_version
attribute during runtime: some old kernels might still check for
kern_version attribute during bpf_prog_load().
Signed-off-by: NRafael David Tinoco <rafaeldtinoco@ubuntu.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NAndrii Nakryiko <andrii@kernel.org>
Acked-by: NJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210323040952.2118241-1-rafaeldtinoco@ubuntu.com
(cherry picked from commit 155f556d)
Signed-off-by: NWang Yufen <wangyufen@huawei.com>

tools/lib/bpf/libbpf.c

@@ -8327,6 +8327,16 @@ int bpf_object__btf_fd(const struct bpf_object *obj)
 	return obj->btf ? btf__fd(obj->btf) : -1;
 }
 
+int bpf_object__set_kversion(struct bpf_object *obj, __u32 kern_version)
+{
+	if (obj->loaded)
+		return -EINVAL;
+
+	obj->kern_version = kern_version;
+
+	return 0;
+}
+
 int bpf_object__set_priv(struct bpf_object *obj, void *priv,
 			 bpf_object_clear_priv_t clear_priv)
 {

tools/lib/bpf/libbpf.h

@@ -143,6 +143,7 @@ LIBBPF_API int bpf_object__unload(struct bpf_object *obj);
 
 LIBBPF_API const char *bpf_object__name(const struct bpf_object *obj);
 LIBBPF_API unsigned int bpf_object__kversion(const struct bpf_object *obj);
+LIBBPF_API int bpf_object__set_kversion(struct bpf_object *obj, __u32 kern_version);
 
 struct btf;
 LIBBPF_API struct btf *bpf_object__btf(const struct bpf_object *obj);

tools/lib/bpf/libbpf.map

@@ -359,4 +359,5 @@ LIBBPF_0.4.0 {
 		bpf_linker__finalize;
 		bpf_linker__free;
 		bpf_linker__new;
+		bpf_object__set_kversion;
 } LIBBPF_0.3.0;