bpf: Append prog->aux->name in bpf_get_prog_name()

This patch makes the bpf_prog's name available
in kallsyms.

The new format is bpf_prog_tag[_name].

Sample kallsyms from running selftests/bpf/test_progs:
[root@arch-fb-vm1 ~]# egrep ' bpf_prog_[0-9a-fA-F]{16}' /proc/kallsyms
ffffffffa0048000 t bpf_prog_dabf0207d1992486_test_obj_id
ffffffffa0038000 t bpf_prog_a04f5eef06a7f555__123456789ABCDE
ffffffffa0050000 t bpf_prog_a04f5eef06a7f555
Signed-off-by: NMartin KaFai Lau <kafai@fb.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@fb.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

kernel/bpf/core.c

@@ -309,12 +309,25 @@ bpf_get_prog_addr_region(const struct bpf_prog *prog,
 
 static void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
 {
+	const char *end = sym + KSYM_NAME_LEN;
+
 	BUILD_BUG_ON(sizeof("bpf_prog_") +
-		     sizeof(prog->tag) * 2 + 1 > KSYM_NAME_LEN);
+		     sizeof(prog->tag) * 2 +
+		     /* name has been null terminated.
+		      * We should need +1 for the '_' preceding
+		      * the name.  However, the null character
+		      * is double counted between the name and the
+		      * sizeof("bpf_prog_") above, so we omit
+		      * the +1 here.
+		      */
+		     sizeof(prog->aux->name) > KSYM_NAME_LEN);
 
 	sym += snprintf(sym, KSYM_NAME_LEN, "bpf_prog_");
 	sym  = bin2hex(sym, prog->tag, sizeof(prog->tag));
-	*sym = 0;
+	if (prog->aux->name[0])
+		snprintf(sym, (size_t)(end - sym), "_%s", prog->aux->name);
+	else
+		*sym = 0;
 }
 
 static __always_inline unsigned long