[PATCH 2/2] genirq: move IRQ thread exit_work object to irqaction

[Richard Patel <ripatel@wii.dev>]

irq_thread() registers irq_thread_dtor() as exit task_work using
a stack-allocated callback_head.  On normal IRQ thread exit, this
work gets cancelled and never runs.

On x86, an abnormal IRQ thread exit (e.g. handler oops) discards
the stack, including the callback_head, while that callback_head
is still pending. By the time exit_task_work() runs, the stack
memory formerly backing callback_head is already clobbered.

  irq_thread()                      <-- on_exit_work allocated
    ** IRQ handler faults **
    oops_end()
      rewind_stack_and_make_dead()  <-- on_exit_work freed
  make_task_dead()
    do_exit(SIGSEGV)
      ...
      exit_shm()                    <-- on_exit_work clobbered
      ...
      exit_task_work()              <-- stack use-after-free
        exit_shm()+0x30             <-- wild jump to return addr

Thus, a benign threaded IRQ oops (e.g. a NULL pointer deref) is
turned into a wild jump. This is caught by kernel IBT:

  ** first fault **
  Oops: general protection fault, kernel NULL pointer dereference 0x3c0: 0000 [#1] SMP NOPTI
  ...
  ** second fault **
  Missing ENDBR: exit_shm+0x30/0x1c0
  kernel BUG at arch/x86/kernel/cet.c:133!
  ...
   ? task_work_run+0x5c/0x90
   ? do_exit+0x209/0x460
   ? rewind_stack_and_make_dead+0x16/0x20
  ...
  note: irq/165-AudioDS[1427] exited with irqs disabled
  Fixing recursive fault but reboot is needed!

Fix this by storing the callback_head in struct irqaction.
The irqaction is only freed once irq_thread_dtor() finishes.

Fixes: 2deb4be28077 ("x86/dumpstack: When OOPSing, rewind the stack before do_exit()")
Cc: stable@vger.kernel.org
Signed-off-by: Richard Patel <ripatel@wii.dev>
---
 include/linux/interrupt.h | 2 ++
 kernel/irq/manage.c       | 9 ++++-----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 52bb684090c0..ee2dd5349697 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -119,6 +119,7 @@ typedef irqreturn_t (*irq_handler_t)(int, void *);
  * @thread_flags:	flags related to @thread
  * @thread_mask:	bitmask for keeping track of @thread activity
  * @dir:	pointer to the proc/irq/NN/name entry
+ * @thread_dtor:	task_work for @thread irregular exit cleanup
  */
 struct irqaction {
 	irq_handler_t		handler;
@@ -137,6 +138,7 @@ struct irqaction {
 	unsigned long		thread_mask;
 	const char		*name;
 	struct proc_dir_entry	*dir;
+	struct callback_head	thread_dtor;
 } ____cacheline_internodealigned_in_smp;
 
 extern irqreturn_t no_action(int cpl, void *dev_id);
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index e882a0693a39..4fbb8f960dbf 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1200,9 +1200,9 @@ static void __irq_thread_dtor(struct irqaction *action)
 	irq_finalize_oneshot(desc, action);
 }
 
-static void irq_thread_dtor(struct callback_head *unused)
+static void irq_thread_dtor(struct callback_head *work)
 {
-	struct irqaction *action = kthread_data(current);
+	struct irqaction *action = container_of(work, struct irqaction, thread_dtor);
 
 	__irq_thread_dtor(action);
 	clear_and_wake_up_bit(IRQTF_EXIT_WORK, &action->thread_flags);
@@ -1249,7 +1249,6 @@ static void wake_up_and_wait_for_irq_thread_ready(struct irq_desc *desc,
  */
 static int irq_thread(void *data)
 {
-	struct callback_head on_exit_work;
 	struct irqaction *action = data;
 	struct irq_desc *desc = irq_to_desc(action->irq);
 	irqreturn_t (*handler_fn)(struct irq_desc *desc,
@@ -1269,8 +1268,8 @@ static int irq_thread(void *data)
 		handler_fn = irq_thread_fn;
 
 	set_bit(IRQTF_EXIT_WORK, &action->thread_flags);
-	init_task_work(&on_exit_work, irq_thread_dtor);
-	task_work_add(current, &on_exit_work, TWA_NONE);
+	init_task_work(&action->thread_dtor, irq_thread_dtor);
+	task_work_add(current, &action->thread_dtor, TWA_NONE);
 
 	while (!irq_wait_for_interrupt(desc, action)) {
 		irqreturn_t action_ret;
-- 
2.52.0