objtool: Make stack validation optional

Make stack validation an explicit cmdline option so that individual
objtool features can be enabled individually by other arches.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/52da143699574d756e65ca4c9d4acaffe9b0fe5f.1650300597.git.jpoimboe@redhat.com

scripts/Makefile.build

@@ -232,6 +232,7 @@ objtool_args =								\
 	$(if $(CONFIG_UNWINDER_ORC), --orc)				\
 	$(if $(CONFIG_RETPOLINE), --retpoline)				\
 	$(if $(CONFIG_SLS), --sls)					\
+	$(if $(CONFIG_STACK_VALIDATION), --stackval)			\
 	$(if $(CONFIG_X86_SMAP), --uaccess)				\
 	$(if $(part-of-module), --module)				\
 	$(if $(CONFIG_FRAME_POINTER),, --no-fp)				\

scripts/link-vmlinux.sh

@@ -126,6 +126,10 @@ objtool_link()
 			objtoolopt="${objtoolopt} --orc"
 		fi
 
+		if is_enabled CONFIG_STACK_VALIDATION; then
+			objtoolopt="${objtoolopt} --stackval"
+		fi
+
 		objtoolopt="${objtoolopt} --lto"
 	fi
 

tools/objtool/builtin-check.c

@@ -39,6 +39,7 @@ const struct option check_options[] = {
 	OPT_BOOLEAN('o', "orc", &opts.orc, "generate ORC metadata"),
 	OPT_BOOLEAN('r', "retpoline", &opts.retpoline, "validate and annotate retpoline usage"),
 	OPT_BOOLEAN('l', "sls", &opts.sls, "validate straight-line-speculation mitigations"),
+	OPT_BOOLEAN('s', "stackval", &opts.stackval, "validate stack unwinding rules"),
 	OPT_BOOLEAN('u', "uaccess", &opts.uaccess, "validate uaccess rules for SMAP"),
 	OPT_CALLBACK_OPTARG(0, "dump", NULL, NULL, "orc", "dump metadata", parse_dump),
 
@@ -92,6 +93,7 @@ static bool opts_valid(void)
 	    opts.orc		||
 	    opts.retpoline	||
 	    opts.sls		||
+	    opts.stackval	||
 	    opts.uaccess) {
 		if (opts.dump_orc) {
 			fprintf(stderr, "--dump can't be combined with other options\n");

tools/objtool/check.c

@@ -3899,25 +3899,27 @@ int check(struct objtool_file *file)
 		warnings += ret;
 	}
 
-	ret = validate_functions(file);
-	if (ret < 0)
-		goto out;
-	warnings += ret;
-
-	ret = validate_unwind_hints(file, NULL);
-	if (ret < 0)
-		goto out;
-	warnings += ret;
+	if (opts.stackval || opts.orc || opts.uaccess || opts.ibt || opts.sls) {
+		ret = validate_functions(file);
+		if (ret < 0)
+			goto out;
+		warnings += ret;
 
-	if (opts.ibt) {
-		ret = validate_ibt(file);
+		ret = validate_unwind_hints(file, NULL);
 		if (ret < 0)
 			goto out;
 		warnings += ret;
+
+		if (!warnings) {
+			ret = validate_reachable_instructions(file);
+			if (ret < 0)
+				goto out;
+			warnings += ret;
+		}
 	}
 
-	if (!warnings) {
-		ret = validate_reachable_instructions(file);
+	if (opts.ibt) {
+		ret = validate_ibt(file);
 		if (ret < 0)
 			goto out;
 		warnings += ret;

tools/objtool/include/objtool/builtin.h

@@ -18,6 +18,7 @@ struct opts {
 	bool orc;
 	bool retpoline;
 	bool sls;
+	bool stackval;
 	bool uaccess;
 
 	/* options: */