[RFC PATCH v2 11/37] tools lib bpf: collect version and license from ELF.

[Wang Nan <wangnan0@huawei.com>]

Expand bpf_obj_elf_collect() to collect license and kernel version
information in eBPF object file. eBPF object file should have a section
named 'license', which contains a string. It should also have a section
named 'version', contains a u32 LINUX_VERSION_CODE.

bpf_obj_validate() is introduced to validate object file after loaded.
Currently it only check existance of 'version' section.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
---
 tools/lib/bpf/libbpf.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 1af80c3..b26f1ee 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -15,12 +15,22 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <asm/unistd.h>
+#include <byteswap.h>
 #include <linux/bpf.h>
 #include <libelf.h>
 #include <gelf.h>
 
 #include "libbpf.h"
 
+#ifdef min
+# undef min
+#endif
+#define min(x, y) ({				\
+	typeof(x) _min1 = (x);			\
+	typeof(y) _min2 = (y);			\
+	(void) (&_min1 == &_min2);		\
+	_min1 < _min2 ? _min1 : _min2; })
+
 #define __printf(a, b)	__attribute__((format(printf, a, b)))
 
 __printf(1, 2)
@@ -70,6 +80,8 @@ void libbpf_set_print(int (*warn)(const char *format, ...),
 struct bpf_object {
 	char *path;
 	bool needs_swap;
+	char license[64];
+	u32 kern_version;
 
 	/*
 	 * Information when doing elf related work. Only valid if fd
@@ -206,6 +218,32 @@ bpf_obj_swap_init(struct bpf_object *obj)
 	}
 }
 
+static int bpf_obj_license_init(struct bpf_object *obj,
+				void *data, size_t size)
+{
+	memcpy(obj->license, data,
+	       min(size, sizeof(obj->license) - 1));
+	pr_debug("license of %s is %s\n", obj->path, obj->license);
+	return 0;
+}
+
+static int bpf_obj_kver_init(struct bpf_object *obj,
+			     void *data, size_t size)
+{
+	u32 kver;
+	if (size < sizeof(kver)) {
+		pr_warning("invalid kver section in %s\n", obj->path);
+		return -EINVAL;
+	}
+	memcpy(&kver, data, sizeof(kver));
+	if (obj->needs_swap)
+		kver = bswap_32(kver);
+	obj->kern_version = kver;
+	pr_debug("kernel version of %s is %x\n", obj->path,
+		 obj->kern_version);
+	return 0;
+}
+
 static int bpf_obj_elf_collect(struct bpf_object *obj)
 {
 	Elf *elf = obj->elf.elf;
@@ -253,11 +291,30 @@ static int bpf_obj_elf_collect(struct bpf_object *obj)
 			 name, (unsigned long)data->d_size,
 			 (int)sh.sh_link, (unsigned long)sh.sh_flags,
 			 (int)sh.sh_type);
+
+		if (strcmp(name, "license") == 0)
+			err = bpf_obj_license_init(obj, data->d_buf,
+						   data->d_size);
+		else if (strcmp(name, "version") == 0)
+			err = bpf_obj_kver_init(obj, data->d_buf,
+						data->d_size);
+		if (err)
+			goto out;
 	}
 out:
 	return err;
 }
 
+static int bpf_obj_validate(struct bpf_object *obj)
+{
+	if (obj->kern_version == 0) {
+		pr_warning("%s doesn't provide kernel version\n",
+			   obj->path);
+		return -EINVAL;
+	}
+	return 0;
+}
+
 struct bpf_object *bpf_open_object(const char *path)
 {
 	struct bpf_object *obj;
@@ -283,6 +340,8 @@ struct bpf_object *bpf_open_object(const char *path)
 		goto out;
 	if (bpf_obj_elf_collect(obj))
 		goto out;
+	if (bpf_obj_validate(obj))
+		goto out;
 
 	return obj;
 
-- 
1.8.3.4