[PATCH 3/4] module: Use a list of strings for ro_after_init sections

Kees Cook
2021-09-01T23:38:07Z

Instead of open-coding the section names, use a list for the sections that
need to be marked read-only after init. Unfortunately, it seems we can't
do normal section merging with scripts/module.lds.S as ld.bfd doesn't
correctly update symbol tables. For more details, see commit 6a3193cdd5e5
("kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG
is enabled").

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-arch@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/asm-generic/vmlinux.lds.h | 4 +++-
kernel/module.c | 28 ++++++++++++++++------------
2 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 4781a8154254..d532baadaeae 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -418,7 +418,9 @@

/*
* Allow architectures to handle ro_after_init data on their
- * own by defining an empty RO_AFTER_INIT_DATA.
+ * own by defining an empty RO_AFTER_INIT_DATA. Any sections
+ * added here must be explicitly marked SHF_RO_AFTER_INIT
+ * via module_sections_ro_after_init[] in kernel/module.c.
*/
#ifndef RO_AFTER_INIT_DATA
#define RO_AFTER_INIT_DATA \
diff --git a/kernel/module.c b/kernel/module.c
index ed13917ea5f3..b0ff82cc48fe 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3514,10 +3514,21 @@ static bool blacklisted(const char *module_name)
}
core_param(module_blacklist, module_blacklist, charp, 0400);

+/*
+ * List of sections to be marked read-only after init. This should match
+ * the RO_AFTER_INIT_DATA macro in include/asm-generic/vmlinux.lds.h.
+ */
+static const char * const module_sections_ro_after_init[] = {
+ ".data..ro_after_init",
+ "__jump_table",
+ NULL
+};
+
static struct module *layout_and_allocate(struct load_info *info, int flags)
{
struct module *mod;
unsigned int ndx;
+ const char * const *section;
int err;

err = check_modinfo(info->mod, info, flags);
@@ -3543,18 +3554,11 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
* layout_sections() can put it in the right place.
* Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.
*/
- ndx = find_sec(info, ".data..ro_after_init");
- if (ndx)
- info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
- /*
- * Mark the __jump_table section as ro_after_init as well: these data
- * structures are never modified, with the exception of entries that
- * refer to code in the __init section, which are annotated as such
- * at module load time.
- */
- ndx = find_sec(info, "__jump_table");
- if (ndx)
- info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
+ for (section = module_sections_ro_after_init; *section; section++) {
+ ndx = find_sec(info, *section);
+ if (ndx)
+ info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
+ }

/*
* Determine total sizes, and put offsets in sh_entsize. For now
--
2.30.2