[PATCH v3 1/3] module: Prepare for addition of new ro_after_init sections

Joel Fernandes (Google)
2019-04-10T19:57:29Z

For the purposes of hardening modules by adding sections to
ro_after_init sections, prepare for addition of new ro_after_init
entries which we do in future patches. Create a table to which new
entries could be added later. This makes it less error prone and reduce
code duplication.

Cc: paulmck@linux.vnet.ibm.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: rcu@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
Cc: kernel-team@android.com
Suggested-by: keescook@chromium.org
Reviewed-by: keescook@chromium.org
Acked-by: rostedt@goodmis.org
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

---
kernel/module.c | 41 +++++++++++++++++++++++------------------
1 file changed, 23 insertions(+), 18 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 524da609c884..42e4e289d6c7 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3300,11 +3300,27 @@ static bool blacklisted(const char *module_name)
}
core_param(module_blacklist, module_blacklist, charp, 0400);

+/*
+ * Mark ro_after_init section with SHF_RO_AFTER_INIT so that
+ * layout_sections() can put it in the right place.
+ * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.
+ */
+static const char * const ro_after_init_sections[] = {
+ ".data..ro_after_init",
+
+ /*
+ * __jump_table 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.
+ */
+ "__jump_table",
+};
+
static struct module *layout_and_allocate(struct load_info *info, int flags)
{
struct module *mod;
unsigned int ndx;
- int err;
+ int err, i;

err = check_modinfo(info->mod, info, flags);
if (err)
@@ -3319,23 +3335,12 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
/* We will do a special allocation for per-cpu sections later. */
info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;

- /*
- * Mark ro_after_init section with SHF_RO_AFTER_INIT so that
- * 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;
+ /* Set sh_flags for read-only after init sections */
+ for (i = 0; i < ARRAY_SIZE(ro_after_init_sections); i++) {
+ ndx = find_sec(info, ro_after_init_sections[i]);
+ if (ndx)
+ info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
+ }

/* Determine total sizes, and put offsets in sh_entsize. For now
this is done generically; there doesn't appear to be any
--
2.21.0.392.gf8f6787159e-goog