kprobes: Prohibit probing on CFI preamble symbol

Do not allow to probe on "__cfi_" or "__pfx_" started symbol, because those
are used for CFI and not executed. Probing it will break the CFI.

Link: https://lore.kernel.org/all/168904024679.116016.18089228029322008512.stgit@devnote2/

Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>
Reviewed-by: Steven Rostedt (Google) <[e-mail]>

kernel/kprobes.c

···
 	return 0;
 }
 
+static bool is_cfi_preamble_symbol(unsigned long addr)
+{
+	char symbuf[KSYM_NAME_LEN];
+
+	if (lookup_symbol_name(addr, symbuf))
+		return false;
+
+	return str_has_prefix("__cfi_", symbuf) ||
+		str_has_prefix("__pfx_", symbuf);
+}
+
 static int check_kprobe_address_safe(struct kprobe *p,
 				     struct module **probed_mod)
 {
···
 	    within_kprobe_blacklist((unsigned long) p->addr) ||
 	    jump_label_text_reserved(p->addr, p->addr) ||
 	    static_call_text_reserved(p->addr, p->addr) ||
-	    find_bug((unsigned long)p->addr)) {
+	    find_bug((unsigned long)p->addr) ||
+	    is_cfi_preamble_symbol((unsigned long)p->addr)) {
 		ret = -EINVAL;
 		goto out;
 	}