[PATCH 05/17] workqueue: cfi: disable callback pointer check with modules

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

With CONFIG_CFI_CLANG, a callback function passed to
__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 != delayed_work_timer_fn);

Disable the warning when CFI and modules are enabled.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
kernel/workqueue.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0d150da252e8..4db267e5ad2d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1630,7 +1630,14 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
struct work_struct *work = &dwork->work;

WARN_ON_ONCE(!wq);
- WARN_ON_ONCE(timer->function != 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 != delayed_work_timer_fn);
+
WARN_ON_ONCE(timer_pending(timer));
WARN_ON_ONCE(!list_empty(&work->entry));

--
2.31.0.rc2.261.g7f71774620-goog