objtool: Add module specific retpoline rules

David allowed retpolines in .init.text, except for modules, which will
trip up objtool retpoline validation, fix that.

Requested-by: David Woodhouse <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Acked-by: Thomas Gleixner <[e-mail]>
Acked-by: Josh Poimboeuf <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Arjan van de Ven <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

scripts/Makefile.build

···
 
 objtool_args = $(if $(CONFIG_UNWINDER_ORC),orc generate,check)
 
+objtool_args += $(if $(part-of-module), --module,)
+
 ifndef CONFIG_FRAME_POINTER
 objtool_args += --no-fp
 endif

tools/objtool/builtin-check.c

···
 #include "builtin.h"
 #include "check.h"
 
-bool no_fp, no_unreachable, retpoline;
+bool no_fp, no_unreachable, retpoline, module;
 
 static const char * const check_usage[] = {
 	"objtool check [<options>] file.o",
···
 	OPT_BOOLEAN('f', "no-fp", &no_fp, "Skip frame pointer validation"),
 	OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"),
 	OPT_BOOLEAN('r', "retpoline", &retpoline, "Validate retpoline assumptions"),
+	OPT_BOOLEAN('m', "module", &module, "Indicates the object will be part of a kernel module"),
 	OPT_END(),
 };
 

tools/objtool/builtin.h

···
 #include <subcmd/parse-options.h>
 
 extern const struct option check_options[];
-extern bool no_fp, no_unreachable, retpoline;
+extern bool no_fp, no_unreachable, retpoline, module;
 
 extern int cmd_check(int argc, const char **argv);
 extern int cmd_orc(int argc, const char **argv);

tools/objtool/check.c

···
 		if (insn->retpoline_safe)
 			continue;
 
+		/*
+		 * .init.text code is ran before userspace and thus doesn't
+		 * strictly need retpolines, except for modules which are
+		 * loaded late, they very much do need retpoline in their
+		 * .init.text
+		 */
+		if (!strcmp(insn->sec->name, ".init.text") && !module)
+			continue;
+
 		WARN_FUNC("indirect %s found in RETPOLINE build",
 			  insn->sec, insn->offset,
 			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");