objtool: Correctly handle retpoline thunk calls

Just like JMP handling, convert a direct CALL to a retpoline thunk
into a retpoline safe indirect CALL.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
Reviewed-by: NMiroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151259.567568238@infradead.org

tools/objtool/check.c

@@ -1025,6 +1025,18 @@ static int add_call_destinations(struct objtool_file *file)
 					  dest_off);
 				return -1;
 			}
+
+		} else if (!strncmp(reloc->sym->name, "__x86_indirect_thunk_", 21)) {
+			/*
+			 * Retpoline calls are really dynamic calls in
+			 * disguise, so convert them accordingly.
+			 */
+			insn->type = INSN_CALL_DYNAMIC;
+			insn->retpoline_safe = true;
+
+			remove_insn_ops(insn);
+			continue;
+
 		} else
 			insn->call_dest = reloc->sym;