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

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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
This commit is contained in:
Michal Kubecek 2023-01-18 11:52:15 +01:00 committed by Peter Zijlstra
parent 3da73f1023
commit 03d7a1053c
2 changed files with 15 additions and 0 deletions
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8
tools/objtool/Documentation/objtool.txt
View file

@ -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.

7
tools/objtool/check.c
View file

@ -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,