genirq: Move interrupt thread exit_work object to irqaction

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

On x86, an abnormal interrupt 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()")
Signed-off-by: Richard Patel <ripatel@wii.dev>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20261009145842.1616117-3-ripatel@wii.dev

1 files changed, 4 insertions, 5 deletions

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 87a2476ea259..3b647d9b458a 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1201,9 +1201,9 @@ 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);
@@ -1250,7 +1250,6 @@ 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,
@@ -1270,8 +1269,8 @@ 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;