From: Michal Kubecek <mkubecek@suse.cz>

Date: Wed, 18 Jan 2023 11:52:15 +0100

Subject: objtool: Check that module init/exit function is an indirect call target

Patch-mainline: Queued in subsystem maintainer repository

Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

Git-commit: 03d7a1053cf72372be22b43faada5bca12ff183d

References: none

Some out-of-tree modules still do not use module_init() / module_exit()

macros and simply create functions with magic names init_module() and

cleanup_module() instead. As a result, these functions are not recognized

as indirect call targets by objtool and such module fails to load into an

IBT enabled kernel.

This old way is not even documented any more but it is cleaner to issue

a warning than to let the module fail on load without obvious reason.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Link: https://lkml.kernel.org/r/20230118105215.B9DA960514@lion.mk-sys.cz

---

 tools/objtool/Documentation/objtool.txt | 8 ++++++++

 tools/objtool/check.c                   | 7 +++++++

 2 files changed, 15 insertions(+)

--- a/tools/objtool/Documentation/objtool.txt

+++ b/tools/objtool/Documentation/objtool.txt

@@ -410,6 +410,14 @@ the objtool maintainers.

    can remove this warning by putting the ANNOTATE_INTRA_FUNCTION_CALL

    directive right before the call.

+12. file.o: warning: func(): not an indirect call target

+

+   This means that objtool is running with --ibt and a function expected

+   to be an indirect call target is not. In particular, this happens for

+   init_module() or cleanup_module() if a module relies on these special

+   names and does not use module_init() / module_exit() macros to create

+   them.

+

 If the error doesn't seem to make sense, it could be a bug in objtool.

 Feel free to ask the objtool maintainer for help.

--- a/tools/objtool/check.c

+++ b/tools/objtool/check.c

@@ -847,8 +847,15 @@ static int create_ibt_endbr_seal_sections(struct objtool_file *file)

 	list_for_each_entry(insn, &file->endbr_list, call_node) {

 		int *site = (int *)sec->data->d_buf + idx;

+		struct symbol *sym = insn->sym;

 		*site = 0;

+		if (opts.module && sym && sym->type == STT_FUNC &&

+		    insn->offset == sym->offset &&

+		    (!strcmp(sym->name, "init_module") ||

+		     !strcmp(sym->name, "cleanup_module")))

+			WARN("%s(): not an indirect call target", sym->name);

+

 		if (elf_add_reloc_to_insn(file->elf, sec,

 					  idx * sizeof(int),

 					  R_X86_64_PC32,