[PATCH 06/17] kthread: cfi: disable callback pointer check with modules

Sami Tolvanen
2021-03-12T00:50:21Z

With CONFIG_CFI_CLANG, a callback function passed to
__kthread_queue_delayed_work from a module points to a jump table
entry defined in the module instead of the one used in the core
kernel, which breaks function address equality in this check:

WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn);

Disable the warning when CFI and modules are enabled.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
kernel/kthread.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 1578973c5740..af5fee350586 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -963,7 +963,13 @@ static void __kthread_queue_delayed_work(struct kthread_worker *worker,
struct timer_list *timer = &dwork->timer;
struct kthread_work *work = &dwork->work;

- WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn);
+ /*
+ * With CFI, timer->function can point to a jump table entry in a module,
+ * which fails the comparison. Disable the warning if CFI and modules are
+ * both enabled.
+ */
+ if (!IS_ENABLED(CONFIG_CFI_CLANG) || !IS_ENABLED(CONFIG_MODULES))
+ WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn);

/*
* If @delay is 0, queue @dwork->work immediately. This is for
--
2.31.0.rc2.261.g7f71774620-goog